Auto merge of #5868 - flip1995:rollup-5g8vft5, r=flip1995

Rollup of 5 pull requests

Successful merges:

 - #5837 (needless_collect: catch x: Vec<_> = iter.collect(); x.into_iter() ...)
 - #5846 (Handle mapping to Option in `map_flatten` lint)
 - #5848 (Add derive_ord_xor_partial_ord lint)
 - #5852 (Add lint for duplicate methods of trait bounds)
 - #5856 (Remove old Symbol reexport)

Failed merges:

r? @ghost

changelog: rollup

20 files changed, 770 insertions, 67 deletions

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 776b04295f9..43d83d978b8 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1454,6 +1454,7 @@ Released 2018-09-13
 [`deprecated_semver`]: https://rust-lang.github.io/rust-clippy/master/index.html#deprecated_semver
 [`deref_addrof`]: https://rust-lang.github.io/rust-clippy/master/index.html#deref_addrof
 [`derive_hash_xor_eq`]: https://rust-lang.github.io/rust-clippy/master/index.html#derive_hash_xor_eq
+[`derive_ord_xor_partial_ord`]: https://rust-lang.github.io/rust-clippy/master/index.html#derive_ord_xor_partial_ord
 [`diverging_sub_expression`]: https://rust-lang.github.io/rust-clippy/master/index.html#diverging_sub_expression
 [`doc_markdown`]: https://rust-lang.github.io/rust-clippy/master/index.html#doc_markdown
 [`double_comparisons`]: https://rust-lang.github.io/rust-clippy/master/index.html#double_comparisons
@@ -1723,6 +1724,7 @@ Released 2018-09-13
 [`too_many_arguments`]: https://rust-lang.github.io/rust-clippy/master/index.html#too_many_arguments
 [`too_many_lines`]: https://rust-lang.github.io/rust-clippy/master/index.html#too_many_lines
 [`toplevel_ref_arg`]: https://rust-lang.github.io/rust-clippy/master/index.html#toplevel_ref_arg
+[`trait_duplication_in_bounds`]: https://rust-lang.github.io/rust-clippy/master/index.html#trait_duplication_in_bounds
 [`transmute_bytes_to_str`]: https://rust-lang.github.io/rust-clippy/master/index.html#transmute_bytes_to_str
 [`transmute_float_to_int`]: https://rust-lang.github.io/rust-clippy/master/index.html#transmute_float_to_int
 [`transmute_int_to_bool`]: https://rust-lang.github.io/rust-clippy/master/index.html#transmute_int_to_bool
diff --git a/clippy_lints/src/attrs.rs b/clippy_lints/src/attrs.rs
index 40af6bb3d7b..3ce110e8e0f 100644
--- a/clippy_lints/src/attrs.rs
+++ b/clippy_lints/src/attrs.rs
@@ -1,6 +1,5 @@
 //! checks for attributes
 
-use crate::reexport::Name;
 use crate::utils::{
     first_line_of_span, is_present_in_source, match_def_path, paths, snippet_opt, span_lint, span_lint_and_help,
     span_lint_and_sugg, span_lint_and_then, without_block_comments,
@@ -517,7 +516,7 @@ fn is_relevant_expr(cx: &LateContext<'_>, typeck_results: &ty::TypeckResults<'_>
     }
 }
 
-fn check_attrs(cx: &LateContext<'_>, span: Span, name: Name, attrs: &[Attribute]) {
+fn check_attrs(cx: &LateContext<'_>, span: Span, name: Symbol, attrs: &[Attribute]) {
     if span.from_expansion() {
         return;
     }
diff --git a/clippy_lints/src/derive.rs b/clippy_lints/src/derive.rs
index 59c62f1ae94..08d8100a885 100644
--- a/clippy_lints/src/derive.rs
+++ b/clippy_lints/src/derive.rs
@@ -1,6 +1,7 @@
 use crate::utils::paths;
 use crate::utils::{
-    is_automatically_derived, is_copy, match_path, span_lint_and_help, span_lint_and_note, span_lint_and_then,
+    get_trait_def_id, is_automatically_derived, is_copy, match_path, span_lint_and_help, span_lint_and_note,
+    span_lint_and_then,
 };
 use if_chain::if_chain;
 use rustc_hir::def_id::DefId;
@@ -44,6 +45,57 @@ declare_clippy_lint! {
 }
 
 declare_clippy_lint! {
+    /// **What it does:** Checks for deriving `Ord` but implementing `PartialOrd`
+    /// explicitly or vice versa.
+    ///
+    /// **Why is this bad?** The implementation of these traits must agree (for
+    /// example for use with `sort`) so it’s probably a bad idea to use a
+    /// default-generated `Ord` implementation with an explicitly defined
+    /// `PartialOrd`. In particular, the following must hold for any type
+    /// implementing `Ord`:
+    ///
+    /// ```text
+    /// k1.cmp(&k2) == k1.partial_cmp(&k2).unwrap()
+    /// ```
+    ///
+    /// **Known problems:** None.
+    ///
+    /// **Example:**
+    ///
+    /// ```rust,ignore
+    /// #[derive(Ord, PartialEq, Eq)]
+    /// struct Foo;
+    ///
+    /// impl PartialOrd for Foo {
+    ///     ...
+    /// }
+    /// ```
+    /// Use instead:
+    /// ```rust,ignore
+    /// #[derive(PartialEq, Eq)]
+    /// struct Foo;
+    ///
+    /// impl PartialOrd for Foo {
+    ///     fn partial_cmp(&self, other: &Foo) -> Option<Ordering> {
+    ///        Some(self.cmp(other))
+    ///     }
+    /// }
+    ///
+    /// impl Ord for Foo {
+    ///     ...
+    /// }
+    /// ```
+    /// or, if you don't need a custom ordering:
+    /// ```rust,ignore
+    /// #[derive(Ord, PartialOrd, PartialEq, Eq)]
+    /// struct Foo;
+    /// ```
+    pub DERIVE_ORD_XOR_PARTIAL_ORD,
+    correctness,
+    "deriving `Ord` but implementing `PartialOrd` explicitly"
+}
+
+declare_clippy_lint! {
     /// **What it does:** Checks for explicit `Clone` implementations for `Copy`
     /// types.
     ///
@@ -103,7 +155,12 @@ declare_clippy_lint! {
     "deriving `serde::Deserialize` on a type that has methods using `unsafe`"
 }
 
-declare_lint_pass!(Derive => [EXPL_IMPL_CLONE_ON_COPY, DERIVE_HASH_XOR_EQ, UNSAFE_DERIVE_DESERIALIZE]);
+declare_lint_pass!(Derive => [
+    EXPL_IMPL_CLONE_ON_COPY,
+    DERIVE_HASH_XOR_EQ,
+    DERIVE_ORD_XOR_PARTIAL_ORD,
+    UNSAFE_DERIVE_DESERIALIZE
+]);
 
 impl<'tcx> LateLintPass<'tcx> for Derive {
     fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx Item<'_>) {
@@ -116,6 +173,7 @@ impl<'tcx> LateLintPass<'tcx> for Derive {
             let is_automatically_derived = is_automatically_derived(&*item.attrs);
 
             check_hash_peq(cx, item.span, trait_ref, ty, is_automatically_derived);
+            check_ord_partial_ord(cx, item.span, trait_ref, ty, is_automatically_derived);
 
             if is_automatically_derived {
                 check_unsafe_derive_deserialize(cx, item, trait_ref, ty);
@@ -180,6 +238,60 @@ fn check_hash_peq<'tcx>(
     }
 }
 
+/// Implementation of the `DERIVE_ORD_XOR_PARTIAL_ORD` lint.
+fn check_ord_partial_ord<'tcx>(
+    cx: &LateContext<'tcx>,
+    span: Span,
+    trait_ref: &TraitRef<'_>,
+    ty: Ty<'tcx>,
+    ord_is_automatically_derived: bool,
+) {
+    if_chain! {
+        if let Some(ord_trait_def_id) = get_trait_def_id(cx, &paths::ORD);
+        if let Some(partial_ord_trait_def_id) = cx.tcx.lang_items().partial_ord_trait();
+        if let Some(def_id) = &trait_ref.trait_def_id();
+        if *def_id == ord_trait_def_id;
+        then {
+            // Look for the PartialOrd implementations for `ty`
+            cx.tcx.for_each_relevant_impl(partial_ord_trait_def_id, ty, |impl_id| {
+                let partial_ord_is_automatically_derived = is_automatically_derived(&cx.tcx.get_attrs(impl_id));
+
+                if partial_ord_is_automatically_derived == ord_is_automatically_derived {
+                    return;
+                }
+
+                let trait_ref = cx.tcx.impl_trait_ref(impl_id).expect("must be a trait implementation");
+
+                // Only care about `impl PartialOrd<Foo> for Foo`
+                // For `impl PartialOrd<B> for A, input_types is [A, B]
+                if trait_ref.substs.type_at(1) == ty {
+                    let mess = if partial_ord_is_automatically_derived {
+                        "you are implementing `Ord` explicitly but have derived `PartialOrd`"
+                    } else {
+                        "you are deriving `Ord` but have implemented `PartialOrd` explicitly"
+                    };
+
+                    span_lint_and_then(
+                        cx,
+                        DERIVE_ORD_XOR_PARTIAL_ORD,
+                        span,
+                        mess,
+                        |diag| {
+                            if let Some(local_def_id) = impl_id.as_local() {
+                                let hir_id = cx.tcx.hir().as_local_hir_id(local_def_id);
+                                diag.span_note(
+                                    cx.tcx.hir().span(hir_id),
+                                    "`PartialOrd` implemented here"
+                                );
+                            }
+                        }
+                    );
+                }
+            });
+        }
+    }
+}
+
 /// Implementation of the `EXPL_IMPL_CLONE_ON_COPY` lint.
 fn check_copy_clone<'tcx>(cx: &LateContext<'tcx>, item: &Item<'_>, trait_ref: &TraitRef<'_>, ty: Ty<'tcx>) {
     if match_path(&trait_ref.path, &paths::CLONE_TRAIT) {
diff --git a/clippy_lints/src/lib.rs b/clippy_lints/src/lib.rs
index f371942dbee..26aff6af8cd 100644
--- a/clippy_lints/src/lib.rs
+++ b/clippy_lints/src/lib.rs
@@ -322,10 +322,6 @@ mod zero_div_zero;
 
 pub use crate::utils::conf::Conf;
 
-mod reexport {
-    pub use rustc_span::Symbol as Name;
-}
-
 /// Register all pre expansion lints
 ///
 /// Pre-expansion lints run before any macro expansion has happened.
@@ -513,6 +509,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
         &default_trait_access::DEFAULT_TRAIT_ACCESS,
         &dereference::EXPLICIT_DEREF_METHODS,
         &derive::DERIVE_HASH_XOR_EQ,
+        &derive::DERIVE_ORD_XOR_PARTIAL_ORD,
         &derive::EXPL_IMPL_CLONE_ON_COPY,
         &derive::UNSAFE_DERIVE_DESERIALIZE,
         &doc::DOC_MARKDOWN,
@@ -786,6 +783,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
         &tabs_in_doc_comments::TABS_IN_DOC_COMMENTS,
         &temporary_assignment::TEMPORARY_ASSIGNMENT,
         &to_digit_is_some::TO_DIGIT_IS_SOME,
+        &trait_bounds::TRAIT_DUPLICATION_IN_BOUNDS,
         &trait_bounds::TYPE_REPETITION_IN_BOUNDS,
         &transmute::CROSSPOINTER_TRANSMUTE,
         &transmute::TRANSMUTE_BYTES_TO_STR,
@@ -1174,6 +1172,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
         LintId::of(&ranges::RANGE_PLUS_ONE),
         LintId::of(&shadow::SHADOW_UNRELATED),
         LintId::of(&strings::STRING_ADD_ASSIGN),
+        LintId::of(&trait_bounds::TRAIT_DUPLICATION_IN_BOUNDS),
         LintId::of(&trait_bounds::TYPE_REPETITION_IN_BOUNDS),
         LintId::of(&trivially_copy_pass_by_ref::TRIVIALLY_COPY_PASS_BY_REF),
         LintId::of(&types::CAST_LOSSLESS),
@@ -1230,6 +1229,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
         LintId::of(&copies::IFS_SAME_COND),
         LintId::of(&copies::IF_SAME_THEN_ELSE),
         LintId::of(&derive::DERIVE_HASH_XOR_EQ),
+        LintId::of(&derive::DERIVE_ORD_XOR_PARTIAL_ORD),
         LintId::of(&doc::MISSING_SAFETY_DOC),
         LintId::of(&doc::NEEDLESS_DOCTEST_MAIN),
         LintId::of(&double_comparison::DOUBLE_COMPARISONS),
@@ -1648,6 +1648,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
         LintId::of(&copies::IFS_SAME_COND),
         LintId::of(&copies::IF_SAME_THEN_ELSE),
         LintId::of(&derive::DERIVE_HASH_XOR_EQ),
+        LintId::of(&derive::DERIVE_ORD_XOR_PARTIAL_ORD),
         LintId::of(&drop_bounds::DROP_BOUNDS),
         LintId::of(&drop_forget_ref::DROP_COPY),
         LintId::of(&drop_forget_ref::DROP_REF),
diff --git a/clippy_lints/src/lifetimes.rs b/clippy_lints/src/lifetimes.rs
index 168f9f953e4..4df6827d77f 100644
--- a/clippy_lints/src/lifetimes.rs
+++ b/clippy_lints/src/lifetimes.rs
@@ -13,9 +13,8 @@ use rustc_lint::{LateContext, LateLintPass};
 use rustc_middle::hir::map::Map;
 use rustc_session::{declare_lint_pass, declare_tool_lint};
 use rustc_span::source_map::Span;
-use rustc_span::symbol::kw;
+use rustc_span::symbol::{kw, Symbol};
 
-use crate::reexport::Name;
 use crate::utils::{in_macro, last_path_segment, span_lint, trait_ref_of_method};
 
 declare_clippy_lint! {
@@ -113,7 +112,7 @@ impl<'tcx> LateLintPass<'tcx> for Lifetimes {
 enum RefLt {
     Unnamed,
     Static,
-    Named(Name),
+    Named(Symbol),
 }
 
 fn check_fn_inner<'tcx>(
@@ -456,7 +455,7 @@ fn has_where_lifetimes<'tcx>(cx: &LateContext<'tcx>, where_clause: &'tcx WhereCl
 }
 
 struct LifetimeChecker {
-    map: FxHashMap<Name, Span>,
+    map: FxHashMap<Symbol, Span>,
 }
 
 impl<'tcx> Visitor<'tcx> for LifetimeChecker {
diff --git a/clippy_lints/src/loops.rs b/clippy_lints/src/loops.rs
index 7e3876ff49b..6359c20040c 100644
--- a/clippy_lints/src/loops.rs
+++ b/clippy_lints/src/loops.rs
@@ -1,14 +1,13 @@
 use crate::consts::constant;
-use crate::reexport::Name;
 use crate::utils::paths;
+use crate::utils::sugg::Sugg;
 use crate::utils::usage::{is_unused, mutated_variables};
 use crate::utils::{
     get_enclosing_block, get_parent_expr, get_trait_def_id, has_iter_method, higher, implements_trait,
-    is_integer_const, is_no_std_crate, is_refutable, last_path_segment, match_trait_method, match_type, match_var,
-    multispan_sugg, snippet, snippet_opt, snippet_with_applicability, span_lint, span_lint_and_help,
-    span_lint_and_sugg, span_lint_and_then, SpanlessEq,
+    is_integer_const, is_no_std_crate, is_refutable, is_type_diagnostic_item, last_path_segment, match_trait_method,
+    match_type, match_var, multispan_sugg, qpath_res, snippet, snippet_opt, snippet_with_applicability, span_lint,
+    span_lint_and_help, span_lint_and_sugg, span_lint_and_then, sugg, SpanlessEq,
 };
-use crate::utils::{is_type_diagnostic_item, qpath_res, sugg};
 use if_chain::if_chain;
 use rustc_ast::ast;
 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
@@ -17,7 +16,7 @@ use rustc_hir::def::{DefKind, Res};
 use rustc_hir::intravisit::{walk_block, walk_expr, walk_pat, walk_stmt, NestedVisitorMap, Visitor};
 use rustc_hir::{
     def_id, BinOpKind, BindingAnnotation, Block, BorrowKind, Expr, ExprKind, GenericArg, HirId, InlineAsmOperand,
-    LoopSource, MatchSource, Mutability, Node, Pat, PatKind, QPath, Stmt, StmtKind,
+    Local, LoopSource, MatchSource, Mutability, Node, Pat, PatKind, QPath, Stmt, StmtKind,
 };
 use rustc_infer::infer::TyCtxtInferExt;
 use rustc_lint::{LateContext, LateLintPass, LintContext};
@@ -27,7 +26,7 @@ use rustc_middle::middle::region;
 use rustc_middle::ty::{self, Ty, TyS};
 use rustc_session::{declare_lint_pass, declare_tool_lint};
 use rustc_span::source_map::Span;
-use rustc_span::symbol::Symbol;
+use rustc_span::symbol::{sym, Ident, Symbol};
 use rustc_typeck::expr_use_visitor::{ConsumeMode, Delegate, ExprUseVisitor, PlaceBase, PlaceWithHirId};
 use std::iter::{once, Iterator};
 use std::mem;
@@ -1184,7 +1183,7 @@ fn check_for_loop_range<'tcx>(
     }
 }
 
-fn is_len_call(expr: &Expr<'_>, var: Name) -> bool {
+fn is_len_call(expr: &Expr<'_>, var: Symbol) -> bool {
     if_chain! {
         if let ExprKind::MethodCall(ref method, _, ref len_args, _) = expr.kind;
         if len_args.len() == 1;
@@ -1640,15 +1639,15 @@ struct VarVisitor<'a, 'tcx> {
     /// var name to look for as index
     var: HirId,
     /// indexed variables that are used mutably
-    indexed_mut: FxHashSet<Name>,
+    indexed_mut: FxHashSet<Symbol>,
     /// indirectly indexed variables (`v[(i + 4) % N]`), the extend is `None` for global
-    indexed_indirectly: FxHashMap<Name, Option<region::Scope>>,
+    indexed_indirectly: FxHashMap<Symbol, Option<region::Scope>>,
     /// subset of `indexed` of vars that are indexed directly: `v[i]`
     /// this will not contain cases like `v[calc_index(i)]` or `v[(i + 4) % N]`
-    indexed_directly: FxHashMap<Name, (Option<region::Scope>, Ty<'tcx>)>,
+    indexed_directly: FxHashMap<Symbol, (Option<region::Scope>, Ty<'tcx>)>,
     /// Any names that are used outside an index operation.
     /// Used to detect things like `&mut vec` used together with `vec[i]`
-    referenced: FxHashSet<Name>,
+    referenced: FxHashSet<Symbol>,
     /// has the loop variable been used in expressions other than the index of
     /// an index op?
     nonindex: bool,
@@ -2004,7 +2003,7 @@ struct InitializeVisitor<'a, 'tcx> {
     end_expr: &'tcx Expr<'tcx>, // the for loop. Stop scanning here.
     var_id: HirId,
     state: VarState,
-    name: Option<Name>,
+    name: Option<Symbol>,
     depth: u32, // depth of conditional expressions
     past_loop: bool,
 }
@@ -2167,7 +2166,7 @@ use self::Nesting::{LookFurther, RuledOut, Unknown};
 
 struct LoopNestVisitor {
     hir_id: HirId,
-    iterator: Name,
+    iterator: Symbol,
     nesting: Nesting,
 }
 
@@ -2218,7 +2217,7 @@ impl<'tcx> Visitor<'tcx> for LoopNestVisitor {
     }
 }
 
-fn path_name(e: &Expr<'_>) -> Option<Name> {
+fn path_name(e: &Expr<'_>) -> Option<Symbol> {
     if let ExprKind::Path(QPath::Resolved(_, ref path)) = e.kind {
         let segments = &path.segments;
         if segments.len() == 1 {
@@ -2358,6 +2357,10 @@ impl<'a, 'tcx> Visitor<'tcx> for VarCollectorVisitor<'a, 'tcx> {
 const NEEDLESS_COLLECT_MSG: &str = "avoid using `collect()` when not needed";
 
 fn check_needless_collect<'tcx>(expr: &'tcx Expr<'_>, cx: &LateContext<'tcx>) {
+    check_needless_collect_direct_usage(expr, cx);
+    check_needless_collect_indirect_usage(expr, cx);
+}
+fn check_needless_collect_direct_usage<'tcx>(expr: &'tcx Expr<'_>, cx: &LateContext<'tcx>) {
     if_chain! {
         if let ExprKind::MethodCall(ref method, _, ref args, _) = expr.kind;
         if let ExprKind::MethodCall(ref chain_method, _, _, _) = args[0].kind;
@@ -2425,6 +2428,157 @@ fn check_needless_collect<'tcx>(expr: &'tcx Expr<'_>, cx: &LateContext<'tcx>) {
     }
 }
 
+fn check_needless_collect_indirect_usage<'tcx>(expr: &'tcx Expr<'_>, cx: &LateContext<'tcx>) {
+    if let ExprKind::Block(ref block, _) = expr.kind {
+        for ref stmt in block.stmts {
+            if_chain! {
+                if let StmtKind::Local(
+                    Local { pat: Pat { kind: PatKind::Binding(_, _, ident, .. ), .. },
+                    init: Some(ref init_expr), .. }
+                ) = stmt.kind;
+                if let ExprKind::MethodCall(ref method_name, _, &[ref iter_source], ..) = init_expr.kind;
+                if method_name.ident.name == sym!(collect) && match_trait_method(cx, &init_expr, &paths::ITERATOR);
+                if let Some(ref generic_args) = method_name.args;
+                if let Some(GenericArg::Type(ref ty)) = generic_args.args.get(0);
+                if let ty = cx.typeck_results().node_type(ty.hir_id);
+                if is_type_diagnostic_item(cx, ty, sym::vec_type) ||
+                    is_type_diagnostic_item(cx, ty, sym!(vecdeque_type)) ||
+                    match_type(cx, ty, &paths::LINKED_LIST);
+                if let Some(iter_calls) = detect_iter_and_into_iters(block, *ident);
+                if iter_calls.len() == 1;
+                then {
+                    // Suggest replacing iter_call with iter_replacement, and removing stmt
+                    let iter_call = &iter_calls[0];
+                    span_lint_and_then(
+                        cx,
+                        NEEDLESS_COLLECT,
+                        stmt.span.until(iter_call.span),
+                        NEEDLESS_COLLECT_MSG,
+                        |diag| {
+                            let iter_replacement = format!("{}{}", Sugg::hir(cx, iter_source, ".."), iter_call.get_iter_method(cx));
+                            diag.multipart_suggestion(
+                                iter_call.get_suggestion_text(),
+                                vec![
+                                    (stmt.span, String::new()),
+                                    (iter_call.span, iter_replacement)
+                                ],
+                                Applicability::MachineApplicable,// MaybeIncorrect,
+                            ).emit();
+                        },
+                    );
+                }
+            }
+        }
+    }
+}
+
+struct IterFunction {
+    func: IterFunctionKind,
+    span: Span,
+}
+impl IterFunction {
+    fn get_iter_method(&self, cx: &LateContext<'_>) -> String {
+        match &self.func {
+            IterFunctionKind::IntoIter => String::new(),
+            IterFunctionKind::Len => String::from(".count()"),
+            IterFunctionKind::IsEmpty => String::from(".next().is_none()"),
+            IterFunctionKind::Contains(span) => format!(".any(|x| x == {})", snippet(cx, *span, "..")),
+        }
+    }
+    fn get_suggestion_text(&self) -> &'static str {
+        match &self.func {
+            IterFunctionKind::IntoIter => {
+                "Use the original Iterator instead of collecting it and then producing a new one"
+            },
+            IterFunctionKind::Len => {
+                "Take the original Iterator's count instead of collecting it and finding the length"
+            },
+            IterFunctionKind::IsEmpty => {
+                "Check if the original Iterator has anything instead of collecting it and seeing if it's empty"
+            },
+            IterFunctionKind::Contains(_) => {
+                "Check if the original Iterator contains an element instead of collecting then checking"
+            },
+        }
+    }
+}
+enum IterFunctionKind {
+    IntoIter,
+    Len,
+    IsEmpty,
+    Contains(Span),
+}
+
+struct IterFunctionVisitor {
+    uses: Vec<IterFunction>,
+    seen_other: bool,
+    target: Ident,
+}
+impl<'tcx> Visitor<'tcx> for IterFunctionVisitor {
+    fn visit_expr(&mut self, expr: &'tcx Expr<'tcx>) {
+        // Check function calls on our collection
+        if_chain! {
+            if let ExprKind::MethodCall(method_name, _, ref args, _) = &expr.kind;
+            if let Some(Expr { kind: ExprKind::Path(QPath::Resolved(_, ref path)), .. }) = args.get(0);
+            if let &[name] = &path.segments;
+            if name.ident == self.target;
+            then {
+                let len = sym!(len);
+                let is_empty = sym!(is_empty);
+                let contains = sym!(contains);
+                match method_name.ident.name {
+                    sym::into_iter => self.uses.push(
+                        IterFunction { func: IterFunctionKind::IntoIter, span: expr.span }
+                    ),
+                    name if name == len => self.uses.push(
+                        IterFunction { func: IterFunctionKind::Len, span: expr.span }
+                    ),
+                    name if name == is_empty => self.uses.push(
+                        IterFunction { func: IterFunctionKind::IsEmpty, span: expr.span }
+                    ),
+                    name if name == contains => self.uses.push(
+                        IterFunction { func: IterFunctionKind::Contains(args[1].span), span: expr.span }
+                    ),
+                    _ => self.seen_other = true,
+                }
+                return
+            }
+        }
+        // Check if the collection is used for anything else
+        if_chain! {
+            if let Expr { kind: ExprKind::Path(QPath::Resolved(_, ref path)), .. } = expr;
+            if let &[name] = &path.segments;
+            if name.ident == self.target;
+            then {
+                self.seen_other = true;
+            } else {
+                walk_expr(self, expr);
+            }
+        }
+    }
+
+    type Map = Map<'tcx>;
+    fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
+        NestedVisitorMap::None
+    }
+}
+
+/// Detect the occurences of calls to `iter` or `into_iter` for the
+/// given identifier
+fn detect_iter_and_into_iters<'tcx>(block: &'tcx Block<'tcx>, identifier: Ident) -> Option<Vec<IterFunction>> {
+    let mut visitor = IterFunctionVisitor {
+        uses: Vec::new(),
+        target: identifier,
+        seen_other: false,
+    };
+    visitor.visit_block(block);
+    if visitor.seen_other {
+        None
+    } else {
+        Some(visitor.uses)
+    }
+}
+
 fn shorten_span(expr: &Expr<'_>, target_fn_name: Symbol) -> Span {
     let mut current_expr = expr;
     while let ExprKind::MethodCall(ref path, ref span, ref args, _) = current_expr.kind {
diff --git a/clippy_lints/src/methods/mod.rs b/clippy_lints/src/methods/mod.rs
index 9edcdd979ff..9217324b18c 100644
--- a/clippy_lints/src/methods/mod.rs
+++ b/clippy_lints/src/methods/mod.rs
@@ -2569,17 +2569,34 @@ fn lint_ok_expect(cx: &LateContext<'_>, expr: &hir::Expr<'_>, ok_args: &[hir::Ex
 fn lint_map_flatten<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx hir::Expr<'_>, map_args: &'tcx [hir::Expr<'_>]) {
     // lint if caller of `.map().flatten()` is an Iterator
     if match_trait_method(cx, expr, &paths::ITERATOR) {
-        let msg = "called `map(..).flatten()` on an `Iterator`. \
-                    This is more succinctly expressed by calling `.flat_map(..)`";
-        let self_snippet = snippet(cx, map_args[0].span, "..");
+        let map_closure_ty = cx.typeck_results().expr_ty(&map_args[1]);
+        let is_map_to_option = match map_closure_ty.kind {
+            ty::Closure(_, _) | ty::FnDef(_, _) | ty::FnPtr(_) => {
+                let map_closure_sig = match map_closure_ty.kind {
+                    ty::Closure(_, substs) => substs.as_closure().sig(),
+                    _ => map_closure_ty.fn_sig(cx.tcx),
+                };
+                let map_closure_return_ty = cx.tcx.erase_late_bound_regions(&map_closure_sig.output());
+                is_type_diagnostic_item(cx, map_closure_return_ty, sym!(option_type))
+            },
+            _ => false,
+        };
+
+        let method_to_use = if is_map_to_option {
+            // `(...).map(...)` has type `impl Iterator<Item=Option<...>>
+            "filter_map"
+        } else {
+            // `(...).map(...)` has type `impl Iterator<Item=impl Iterator<...>>
+            "flat_map"
+        };
         let func_snippet = snippet(cx, map_args[1].span, "..");
-        let hint = format!("{0}.flat_map({1})", self_snippet, func_snippet);
+        let hint = format!(".{0}({1})", method_to_use, func_snippet);
         span_lint_and_sugg(
             cx,
             MAP_FLATTEN,
-            expr.span,
-            msg,
-            "try using `flat_map` instead",
+            expr.span.with_lo(map_args[0].span.hi()),
+            "called `map(..).flatten()` on an `Iterator`",
+            &format!("try using `{}` instead", method_to_use),
             hint,
             Applicability::MachineApplicable,
         );
@@ -2587,16 +2604,13 @@ fn lint_map_flatten<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx hir::Expr<'_>, map
 
     // lint if caller of `.map().flatten()` is an Option
     if is_type_diagnostic_item(cx, cx.typeck_results().expr_ty(&map_args[0]), sym!(option_type)) {
-        let msg = "called `map(..).flatten()` on an `Option`. \
-                    This is more succinctly expressed by calling `.and_then(..)`";
-        let self_snippet = snippet(cx, map_args[0].span, "..");
         let func_snippet = snippet(cx, map_args[1].span, "..");
-        let hint = format!("{0}.and_then({1})", self_snippet, func_snippet);
+        let hint = format!(".and_then({})", func_snippet);
         span_lint_and_sugg(
             cx,
             MAP_FLATTEN,
-            expr.span,
-            msg,
+            expr.span.with_lo(map_args[0].span.hi()),
+            "called `map(..).flatten()` on an `Option`",
             "try using `and_then` instead",
             hint,
             Applicability::MachineApplicable,
diff --git a/clippy_lints/src/shadow.rs b/clippy_lints/src/shadow.rs
index 6f03e92bde3..2610157763a 100644
--- a/clippy_lints/src/shadow.rs
+++ b/clippy_lints/src/shadow.rs
@@ -1,4 +1,3 @@
-use crate::reexport::Name;
 use crate::utils::{contains_name, higher, iter_input_pats, snippet, span_lint_and_then};
 use rustc_hir::intravisit::FnKind;
 use rustc_hir::{
@@ -10,6 +9,7 @@ use rustc_middle::lint::in_external_macro;
 use rustc_middle::ty;
 use rustc_session::{declare_lint_pass, declare_tool_lint};
 use rustc_span::source_map::Span;
+use rustc_span::symbol::Symbol;
 
 declare_clippy_lint! {
     /// **What it does:** Checks for bindings that shadow other bindings already in
@@ -123,7 +123,7 @@ fn check_fn<'tcx>(cx: &LateContext<'tcx>, decl: &'tcx FnDecl<'_>, body: &'tcx Bo
     check_expr(cx, &body.value, &mut bindings);
 }
 
-fn check_block<'tcx>(cx: &LateContext<'tcx>, block: &'tcx Block<'_>, bindings: &mut Vec<(Name, Span)>) {
+fn check_block<'tcx>(cx: &LateContext<'tcx>, block: &'tcx Block<'_>, bindings: &mut Vec<(Symbol, Span)>) {
     let len = bindings.len();
     for stmt in block.stmts {
         match stmt.kind {
@@ -138,7 +138,7 @@ fn check_block<'tcx>(cx: &LateContext<'tcx>, block: &'tcx Block<'_>, bindings: &
     bindings.truncate(len);
 }
 
-fn check_local<'tcx>(cx: &LateContext<'tcx>, local: &'tcx Local<'_>, bindings: &mut Vec<(Name, Span)>) {
+fn check_local<'tcx>(cx: &LateContext<'tcx>, local: &'tcx Local<'_>, bindings: &mut Vec<(Symbol, Span)>) {
     if in_external_macro(cx.sess(), local.span) {
         return;
     }
@@ -173,7 +173,7 @@ fn check_pat<'tcx>(
     pat: &'tcx Pat<'_>,
     init: Option<&'tcx Expr<'_>>,
     span: Span,
-    bindings: &mut Vec<(Name, Span)>,
+    bindings: &mut Vec<(Symbol, Span)>,
 ) {
     // TODO: match more stuff / destructuring
     match pat.kind {
@@ -254,7 +254,7 @@ fn check_pat<'tcx>(
 
 fn lint_shadow<'tcx>(
     cx: &LateContext<'tcx>,
-    name: Name,
+    name: Symbol,
     span: Span,
     pattern_span: Span,
     init: Option<&'tcx Expr<'_>>,
@@ -315,7 +315,7 @@ fn lint_shadow<'tcx>(
     }
 }
 
-fn check_expr<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>, bindings: &mut Vec<(Name, Span)>) {
+fn check_expr<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>, bindings: &mut Vec<(Symbol, Span)>) {
     if in_external_macro(cx.sess(), expr.span) {
         return;
     }
@@ -351,7 +351,7 @@ fn check_expr<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>, bindings: &mut
     }
 }
 
-fn check_ty<'tcx>(cx: &LateContext<'tcx>, ty: &'tcx Ty<'_>, bindings: &mut Vec<(Name, Span)>) {
+fn check_ty<'tcx>(cx: &LateContext<'tcx>, ty: &'tcx Ty<'_>, bindings: &mut Vec<(Symbol, Span)>) {
     match ty.kind {
         TyKind::Slice(ref sty) => check_ty(cx, sty, bindings),
         TyKind::Array(ref fty, ref anon_const) => {
@@ -371,7 +371,7 @@ fn check_ty<'tcx>(cx: &LateContext<'tcx>, ty: &'tcx Ty<'_>, bindings: &mut Vec<(
     }
 }
 
-fn is_self_shadow(name: Name, expr: &Expr<'_>) -> bool {
+fn is_self_shadow(name: Symbol, expr: &Expr<'_>) -> bool {
     match expr.kind {
         ExprKind::Box(ref inner) | ExprKind::AddrOf(_, _, ref inner) => is_self_shadow(name, inner),
         ExprKind::Block(ref block, _) => {
@@ -383,6 +383,6 @@ fn is_self_shadow(name: Name, expr: &Expr<'_>) -> bool {
     }
 }
 
-fn path_eq_name(name: Name, path: &Path<'_>) -> bool {
+fn path_eq_name(name: Symbol, path: &Path<'_>) -> bool {
     !path.is_global() && path.segments.len() == 1 && path.segments[0].ident.as_str() == name.as_str()
 }
diff --git a/clippy_lints/src/trait_bounds.rs b/clippy_lints/src/trait_bounds.rs
index 0ef70311fb1..06631f89f27 100644
--- a/clippy_lints/src/trait_bounds.rs
+++ b/clippy_lints/src/trait_bounds.rs
@@ -2,9 +2,10 @@ use crate::utils::{in_macro, snippet, snippet_with_applicability, span_lint_and_
 use if_chain::if_chain;
 use rustc_data_structures::fx::FxHashMap;
 use rustc_errors::Applicability;
-use rustc_hir::{GenericBound, Generics, WherePredicate};
+use rustc_hir::{def::Res, GenericBound, Generics, ParamName, Path, QPath, TyKind, WherePredicate};
 use rustc_lint::{LateContext, LateLintPass};
 use rustc_session::{declare_tool_lint, impl_lint_pass};
+use rustc_span::Span;
 
 declare_clippy_lint! {
     /// **What it does:** This lint warns about unnecessary type repetitions in trait bounds
@@ -29,6 +30,35 @@ declare_clippy_lint! {
     "Types are repeated unnecessary in trait bounds use `+` instead of using `T: _, T: _`"
 }
 
+declare_clippy_lint! {
+    /// **What it does:** Checks for cases where generics are being used and multiple
+    /// syntax specifications for trait bounds are used simultaneously.
+    ///
+    /// **Why is this bad?** Duplicate bounds makes the code
+    /// less readable than specifing them only once.
+    ///
+    /// **Known problems:** None.
+    ///
+    /// **Example:**
+    /// ```rust
+    /// fn func<T: Clone + Default>(arg: T) where T: Clone + Default {}
+    /// ```
+    ///
+    /// Could be written as:
+    ///
+    /// ```rust
+    /// fn func<T: Clone + Default>(arg: T) {}
+    /// ```
+    /// or
+    ///  ///
+    /// ```rust
+    /// fn func<T>(arg: T) where T: Clone + Default {}
+    /// ```
+    pub TRAIT_DUPLICATION_IN_BOUNDS,
+    pedantic,
+    "Check if the same trait bounds are specified twice during a function declaration"
+}
+
 #[derive(Copy, Clone)]
 pub struct TraitBounds {
     max_trait_bounds: u64,
@@ -41,10 +71,25 @@ impl TraitBounds {
     }
 }
 
-impl_lint_pass!(TraitBounds => [TYPE_REPETITION_IN_BOUNDS]);
+impl_lint_pass!(TraitBounds => [TYPE_REPETITION_IN_BOUNDS, TRAIT_DUPLICATION_IN_BOUNDS]);
 
 impl<'tcx> LateLintPass<'tcx> for TraitBounds {
     fn check_generics(&mut self, cx: &LateContext<'tcx>, gen: &'tcx Generics<'_>) {
+        self.check_type_repetition(cx, gen);
+        check_trait_bound_duplication(cx, gen);
+    }
+}
+
+fn get_trait_res_span_from_bound(bound: &GenericBound<'_>) -> Option<(Res, Span)> {
+    if let GenericBound::Trait(t, _) = bound {
+        Some((t.trait_ref.path.res, t.span))
+    } else {
+        None
+    }
+}
+
+impl TraitBounds {
+    fn check_type_repetition(self, cx: &LateContext<'_>, gen: &'_ Generics<'_>) {
         if in_macro(gen.span) {
             return;
         }
@@ -101,3 +146,48 @@ impl<'tcx> LateLintPass<'tcx> for TraitBounds {
         }
     }
 }
+
+fn check_trait_bound_duplication(cx: &LateContext<'_>, gen: &'_ Generics<'_>) {
+    if in_macro(gen.span) || gen.params.is_empty() || gen.where_clause.predicates.is_empty() {
+        return;
+    }
+
+    let mut map = FxHashMap::default();
+    for param in gen.params {
+        if let ParamName::Plain(ref ident) = param.name {
+            let res = param
+                .bounds
+                .iter()
+                .filter_map(get_trait_res_span_from_bound)
+                .collect::<Vec<_>>();
+            map.insert(*ident, res);
+        }
+    }
+
+    for predicate in gen.where_clause.predicates {
+        if_chain! {
+            if let WherePredicate::BoundPredicate(ref bound_predicate) = predicate;
+            if !in_macro(bound_predicate.span);
+            if let TyKind::Path(ref path) = bound_predicate.bounded_ty.kind;
+            if let QPath::Resolved(_, Path { ref segments, .. }) = path;
+            if let Some(segment) = segments.first();
+            if let Some(trait_resolutions_direct) = map.get(&segment.ident);
+            then {
+                for (res_where, _) in bound_predicate.bounds.iter().filter_map(get_trait_res_span_from_bound) {
+                    if let Some((_, span_direct)) = trait_resolutions_direct
+                                                .iter()
+                                                .find(|(res_direct, _)| *res_direct == res_where) {
+                        span_lint_and_help(
+                            cx,
+                            TRAIT_DUPLICATION_IN_BOUNDS,
+                            *span_direct,
+                            "this trait bound is already specified in the where clause",
+                            None,
+                            "consider removing this trait bound",
+                        );
+                    }
+                }
+            }
+        }
+    }
+}
diff --git a/clippy_lints/src/utils/mod.rs b/clippy_lints/src/utils/mod.rs
index 3f8e15d9029..214bfb7dda2 100644
--- a/clippy_lints/src/utils/mod.rs
+++ b/clippy_lints/src/utils/mod.rs
@@ -52,7 +52,6 @@ use rustc_trait_selection::traits::query::normalize::AtExt;
 use smallvec::SmallVec;
 
 use crate::consts::{constant, Constant};
-use crate::reexport::Name;
 
 /// Returns `true` if the two spans come from differing expansions (i.e., one is
 /// from a macro and one isn't).
@@ -150,7 +149,7 @@ pub fn match_trait_method(cx: &LateContext<'_>, expr: &Expr<'_>, path: &[&str])
 }
 
 /// Checks if an expression references a variable of the given name.
-pub fn match_var(expr: &Expr<'_>, var: Name) -> bool {
+pub fn match_var(expr: &Expr<'_>, var: Symbol) -> bool {
     if let ExprKind::Path(QPath::Resolved(None, ref path)) = expr.kind {
         if let [p] = path.segments {
             return p.ident.name == var;
@@ -420,7 +419,7 @@ pub fn is_entrypoint_fn(cx: &LateContext<'_>, def_id: DefId) -> bool {
 }
 
 /// Gets the name of the item the expression is in, if available.
-pub fn get_item_name(cx: &LateContext<'_>, expr: &Expr<'_>) -> Option<Name> {
+pub fn get_item_name(cx: &LateContext<'_>, expr: &Expr<'_>) -> Option<Symbol> {
     let parent_id = cx.tcx.hir().get_parent_item(expr.hir_id);
     match cx.tcx.hir().find(parent_id) {
         Some(
@@ -433,7 +432,7 @@ pub fn get_item_name(cx: &LateContext<'_>, expr: &Expr<'_>) -> Option<Name> {
 }
 
 /// Gets the name of a `Pat`, if any.
-pub fn get_pat_name(pat: &Pat<'_>) -> Option<Name> {
+pub fn get_pat_name(pat: &Pat<'_>) -> Option<Symbol> {
     match pat.kind {
         PatKind::Binding(.., ref spname, _) => Some(spname.name),
         PatKind::Path(ref qpath) => single_segment_path(qpath).map(|ps| ps.ident.name),
@@ -443,14 +442,14 @@ pub fn get_pat_name(pat: &Pat<'_>) -> Option<Name> {
 }
 
 struct ContainsName {
-    name: Name,
+    name: Symbol,
     result: bool,
 }
 
 impl<'tcx> Visitor<'tcx> for ContainsName {
     type Map = Map<'tcx>;
 
-    fn visit_name(&mut self, _: Span, name: Name) {
+    fn visit_name(&mut self, _: Span, name: Symbol) {
         if self.name == name {
             self.result = true;
         }
@@ -461,7 +460,7 @@ impl<'tcx> Visitor<'tcx> for ContainsName {
 }
 
 /// Checks if an `Expr` contains a certain name.
-pub fn contains_name(name: Name, expr: &Expr<'_>) -> bool {
+pub fn contains_name(name: Symbol, expr: &Expr<'_>) -> bool {
     let mut cn = ContainsName { name, result: false };
     cn.visit_expr(expr);
     cn.result
@@ -1027,7 +1026,7 @@ pub fn is_allowed(cx: &LateContext<'_>, lint: &'static Lint, id: HirId) -> bool
     cx.tcx.lint_level_at_node(lint, id).0 == Level::Allow
 }
 
-pub fn get_arg_name(pat: &Pat<'_>) -> Option<Name> {
+pub fn get_arg_name(pat: &Pat<'_>) -> Option<Symbol> {
     match pat.kind {
         PatKind::Binding(.., ident, None) => Some(ident.name),
         PatKind::Ref(ref subpat, _) => get_arg_name(subpat),
diff --git a/src/lintlist/mod.rs b/src/lintlist/mod.rs
index 1879aae77fb..a08d7da6dcb 100644
--- a/src/lintlist/mod.rs
+++ b/src/lintlist/mod.rs
@@ -361,6 +361,13 @@ pub static ref ALL_LINTS: Vec<Lint> = vec![
         module: "derive",
     },
     Lint {
+        name: "derive_ord_xor_partial_ord",
+        group: "correctness",
+        desc: "deriving `Ord` but implementing `PartialOrd` explicitly",
+        deprecation: None,
+        module: "derive",
+    },
+    Lint {
         name: "diverging_sub_expression",
         group: "complexity",
         desc: "whether an expression contains a diverging sub expression",
@@ -2167,6 +2174,13 @@ pub static ref ALL_LINTS: Vec<Lint> = vec![
         module: "misc",
     },
     Lint {
+        name: "trait_duplication_in_bounds",
+        group: "pedantic",
+        desc: "Check if the same trait bounds are specified twice during a function declaration",
+        deprecation: None,
+        module: "trait_bounds",
+    },
+    Lint {
         name: "transmute_bytes_to_str",
         group: "complexity",
         desc: "transmutes from a `&[u8]` to a `&str`",
diff --git a/tests/ui/derive_ord_xor_partial_ord.rs b/tests/ui/derive_ord_xor_partial_ord.rs
new file mode 100644
index 00000000000..b82dc518a3b
--- /dev/null
+++ b/tests/ui/derive_ord_xor_partial_ord.rs
@@ -0,0 +1,68 @@
+#![warn(clippy::derive_ord_xor_partial_ord)]
+
+use std::cmp::Ordering;
+
+#[derive(PartialOrd, Ord, PartialEq, Eq)]
+struct DeriveBoth;
+
+impl PartialEq<u64> for DeriveBoth {
+    fn eq(&self, _: &u64) -> bool {
+        true
+    }
+}
+
+impl PartialOrd<u64> for DeriveBoth {
+    fn partial_cmp(&self, _: &u64) -> Option<Ordering> {
+        Some(Ordering::Equal)
+    }
+}
+
+#[derive(Ord, PartialEq, Eq)]
+struct DeriveOrd;
+
+impl PartialOrd for DeriveOrd {
+    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
+        Some(other.cmp(self))
+    }
+}
+
+#[derive(Ord, PartialEq, Eq)]
+struct DeriveOrdWithExplicitTypeVariable;
+
+impl PartialOrd<DeriveOrdWithExplicitTypeVariable> for DeriveOrdWithExplicitTypeVariable {
+    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
+        Some(other.cmp(self))
+    }
+}
+
+#[derive(PartialOrd, PartialEq, Eq)]
+struct DerivePartialOrd;
+
+impl std::cmp::Ord for DerivePartialOrd {
+    fn cmp(&self, other: &Self) -> Ordering {
+        Ordering::Less
+    }
+}
+
+#[derive(PartialOrd, PartialEq, Eq)]
+struct ImplUserOrd;
+
+trait Ord {}
+
+// We don't want to lint on user-defined traits called `Ord`
+impl Ord for ImplUserOrd {}
+
+mod use_ord {
+    use std::cmp::{Ord, Ordering};
+
+    #[derive(PartialOrd, PartialEq, Eq)]
+    struct DerivePartialOrdInUseOrd;
+
+    impl Ord for DerivePartialOrdInUseOrd {
+        fn cmp(&self, other: &Self) -> Ordering {
+            Ordering::Less
+        }
+    }
+}
+
+fn main() {}
diff --git a/tests/ui/derive_ord_xor_partial_ord.stderr b/tests/ui/derive_ord_xor_partial_ord.stderr
new file mode 100644
index 00000000000..66bc4d42ce8
--- /dev/null
+++ b/tests/ui/derive_ord_xor_partial_ord.stderr
@@ -0,0 +1,71 @@
+error: you are deriving `Ord` but have implemented `PartialOrd` explicitly
+  --> $DIR/derive_ord_xor_partial_ord.rs:20:10
+   |
+LL | #[derive(Ord, PartialEq, Eq)]
+   |          ^^^
+   |
+   = note: `-D clippy::derive-ord-xor-partial-ord` implied by `-D warnings`
+note: `PartialOrd` implemented here
+  --> $DIR/derive_ord_xor_partial_ord.rs:23:1
+   |
+LL | / impl PartialOrd for DeriveOrd {
+LL | |     fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
+LL | |         Some(other.cmp(self))
+LL | |     }
+LL | | }
+   | |_^
+   = note: this error originates in a derive macro (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error: you are deriving `Ord` but have implemented `PartialOrd` explicitly
+  --> $DIR/derive_ord_xor_partial_ord.rs:29:10
+   |
+LL | #[derive(Ord, PartialEq, Eq)]
+   |          ^^^
+   |
+note: `PartialOrd` implemented here
+  --> $DIR/derive_ord_xor_partial_ord.rs:32:1
+   |
+LL | / impl PartialOrd<DeriveOrdWithExplicitTypeVariable> for DeriveOrdWithExplicitTypeVariable {
+LL | |     fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
+LL | |         Some(other.cmp(self))
+LL | |     }
+LL | | }
+   | |_^
+   = note: this error originates in a derive macro (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error: you are implementing `Ord` explicitly but have derived `PartialOrd`
+  --> $DIR/derive_ord_xor_partial_ord.rs:41:1
+   |
+LL | / impl std::cmp::Ord for DerivePartialOrd {
+LL | |     fn cmp(&self, other: &Self) -> Ordering {
+LL | |         Ordering::Less
+LL | |     }
+LL | | }
+   | |_^
+   |
+note: `PartialOrd` implemented here
+  --> $DIR/derive_ord_xor_partial_ord.rs:38:10
+   |
+LL | #[derive(PartialOrd, PartialEq, Eq)]
+   |          ^^^^^^^^^^
+   = note: this error originates in a derive macro (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error: you are implementing `Ord` explicitly but have derived `PartialOrd`
+  --> $DIR/derive_ord_xor_partial_ord.rs:61:5
+   |
+LL | /     impl Ord for DerivePartialOrdInUseOrd {
+LL | |         fn cmp(&self, other: &Self) -> Ordering {
+LL | |             Ordering::Less
+LL | |         }
+LL | |     }
+   | |_____^
+   |
+note: `PartialOrd` implemented here
+  --> $DIR/derive_ord_xor_partial_ord.rs:58:14
+   |
+LL |     #[derive(PartialOrd, PartialEq, Eq)]
+   |              ^^^^^^^^^^
+   = note: this error originates in a derive macro (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error: aborting due to 4 previous errors
+
diff --git a/tests/ui/map_flatten.fixed b/tests/ui/map_flatten.fixed
index 4171d80f48a..a5fdf7df613 100644
--- a/tests/ui/map_flatten.fixed
+++ b/tests/ui/map_flatten.fixed
@@ -5,6 +5,20 @@
 #![allow(clippy::map_identity)]
 
 fn main() {
+    // mapping to Option on Iterator
+    fn option_id(x: i8) -> Option<i8> {
+        Some(x)
+    }
+    let option_id_ref: fn(i8) -> Option<i8> = option_id;
+    let option_id_closure = |x| Some(x);
+    let _: Vec<_> = vec![5_i8; 6].into_iter().filter_map(option_id).collect();
+    let _: Vec<_> = vec![5_i8; 6].into_iter().filter_map(option_id_ref).collect();
+    let _: Vec<_> = vec![5_i8; 6].into_iter().filter_map(option_id_closure).collect();
+    let _: Vec<_> = vec![5_i8; 6].into_iter().filter_map(|x| x.checked_add(1)).collect();
+
+    // mapping to Iterator on Iterator
     let _: Vec<_> = vec![5_i8; 6].into_iter().flat_map(|x| 0..x).collect();
+
+    // mapping to Option on Option
     let _: Option<_> = (Some(Some(1))).and_then(|x| x);
 }
diff --git a/tests/ui/map_flatten.rs b/tests/ui/map_flatten.rs
index 16a0fd090ad..abbc4e16e56 100644
--- a/tests/ui/map_flatten.rs
+++ b/tests/ui/map_flatten.rs
@@ -5,6 +5,20 @@
 #![allow(clippy::map_identity)]
 
 fn main() {
+    // mapping to Option on Iterator
+    fn option_id(x: i8) -> Option<i8> {
+        Some(x)
+    }
+    let option_id_ref: fn(i8) -> Option<i8> = option_id;
+    let option_id_closure = |x| Some(x);
+    let _: Vec<_> = vec![5_i8; 6].into_iter().map(option_id).flatten().collect();
+    let _: Vec<_> = vec![5_i8; 6].into_iter().map(option_id_ref).flatten().collect();
+    let _: Vec<_> = vec![5_i8; 6].into_iter().map(option_id_closure).flatten().collect();
+    let _: Vec<_> = vec![5_i8; 6].into_iter().map(|x| x.checked_add(1)).flatten().collect();
+
+    // mapping to Iterator on Iterator
     let _: Vec<_> = vec![5_i8; 6].into_iter().map(|x| 0..x).flatten().collect();
+
+    // mapping to Option on Option
     let _: Option<_> = (Some(Some(1))).map(|x| x).flatten();
 }
diff --git a/tests/ui/map_flatten.stderr b/tests/ui/map_flatten.stderr
index 00bc41c15e9..b6479cd69ea 100644
--- a/tests/ui/map_flatten.stderr
+++ b/tests/ui/map_flatten.stderr
@@ -1,16 +1,40 @@
-error: called `map(..).flatten()` on an `Iterator`. This is more succinctly expressed by calling `.flat_map(..)`
-  --> $DIR/map_flatten.rs:8:21
+error: called `map(..).flatten()` on an `Iterator`
+  --> $DIR/map_flatten.rs:14:46
    |
-LL |     let _: Vec<_> = vec![5_i8; 6].into_iter().map(|x| 0..x).flatten().collect();
-   |                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try using `flat_map` instead: `vec![5_i8; 6].into_iter().flat_map(|x| 0..x)`
+LL |     let _: Vec<_> = vec![5_i8; 6].into_iter().map(option_id).flatten().collect();
+   |                                              ^^^^^^^^^^^^^^^^^^^^^^^^^ help: try using `filter_map` instead: `.filter_map(option_id)`
    |
    = note: `-D clippy::map-flatten` implied by `-D warnings`
 
-error: called `map(..).flatten()` on an `Option`. This is more succinctly expressed by calling `.and_then(..)`
-  --> $DIR/map_flatten.rs:9:24
+error: called `map(..).flatten()` on an `Iterator`
+  --> $DIR/map_flatten.rs:15:46
+   |
+LL |     let _: Vec<_> = vec![5_i8; 6].into_iter().map(option_id_ref).flatten().collect();
+   |                                              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try using `filter_map` instead: `.filter_map(option_id_ref)`
+
+error: called `map(..).flatten()` on an `Iterator`
+  --> $DIR/map_flatten.rs:16:46
+   |
+LL |     let _: Vec<_> = vec![5_i8; 6].into_iter().map(option_id_closure).flatten().collect();
+   |                                              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try using `filter_map` instead: `.filter_map(option_id_closure)`
+
+error: called `map(..).flatten()` on an `Iterator`
+  --> $DIR/map_flatten.rs:17:46
+   |
+LL |     let _: Vec<_> = vec![5_i8; 6].into_iter().map(|x| x.checked_add(1)).flatten().collect();
+   |                                              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try using `filter_map` instead: `.filter_map(|x| x.checked_add(1))`
+
+error: called `map(..).flatten()` on an `Iterator`
+  --> $DIR/map_flatten.rs:20:46
+   |
+LL |     let _: Vec<_> = vec![5_i8; 6].into_iter().map(|x| 0..x).flatten().collect();
+   |                                              ^^^^^^^^^^^^^^^^^^^^^^^^ help: try using `flat_map` instead: `.flat_map(|x| 0..x)`
+
+error: called `map(..).flatten()` on an `Option`
+  --> $DIR/map_flatten.rs:23:39
    |
 LL |     let _: Option<_> = (Some(Some(1))).map(|x| x).flatten();
-   |                        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try using `and_then` instead: `(Some(Some(1))).and_then(|x| x)`
+   |                                       ^^^^^^^^^^^^^^^^^^^^^ help: try using `and_then` instead: `.and_then(|x| x)`
 
-error: aborting due to 2 previous errors
+error: aborting due to 6 previous errors
 
diff --git a/tests/ui/needless_collect_indirect.rs b/tests/ui/needless_collect_indirect.rs
new file mode 100644
index 00000000000..4cf03e82035
--- /dev/null
+++ b/tests/ui/needless_collect_indirect.rs
@@ -0,0 +1,19 @@
+use std::collections::{HashMap, VecDeque};
+
+fn main() {
+    let sample = [1; 5];
+    let indirect_iter = sample.iter().collect::<Vec<_>>();
+    indirect_iter.into_iter().map(|x| (x, x + 1)).collect::<HashMap<_, _>>();
+    let indirect_len = sample.iter().collect::<VecDeque<_>>();
+    indirect_len.len();
+    let indirect_empty = sample.iter().collect::<VecDeque<_>>();
+    indirect_empty.is_empty();
+    let indirect_contains = sample.iter().collect::<VecDeque<_>>();
+    indirect_contains.contains(&&5);
+    let indirect_negative = sample.iter().collect::<Vec<_>>();
+    indirect_negative.len();
+    indirect_negative
+        .into_iter()
+        .map(|x| (*x, *x + 1))
+        .collect::<HashMap<_, _>>();
+}
diff --git a/tests/ui/needless_collect_indirect.stderr b/tests/ui/needless_collect_indirect.stderr
new file mode 100644
index 00000000000..0c1e61d7496
--- /dev/null
+++ b/tests/ui/needless_collect_indirect.stderr
@@ -0,0 +1,55 @@
+error: avoid using `collect()` when not needed
+  --> $DIR/needless_collect_indirect.rs:5:5
+   |
+LL | /     let indirect_iter = sample.iter().collect::<Vec<_>>();
+LL | |     indirect_iter.into_iter().map(|x| (x, x + 1)).collect::<HashMap<_, _>>();
+   | |____^
+   |
+   = note: `-D clippy::needless-collect` implied by `-D warnings`
+help: Use the original Iterator instead of collecting it and then producing a new one
+   |
+LL |     
+LL |     sample.iter().map(|x| (x, x + 1)).collect::<HashMap<_, _>>();
+   |
+
+error: avoid using `collect()` when not needed
+  --> $DIR/needless_collect_indirect.rs:7:5
+   |
+LL | /     let indirect_len = sample.iter().collect::<VecDeque<_>>();
+LL | |     indirect_len.len();
+   | |____^
+   |
+help: Take the original Iterator's count instead of collecting it and finding the length
+   |
+LL |     
+LL |     sample.iter().count();
+   |
+
+error: avoid using `collect()` when not needed
+  --> $DIR/needless_collect_indirect.rs:9:5
+   |
+LL | /     let indirect_empty = sample.iter().collect::<VecDeque<_>>();
+LL | |     indirect_empty.is_empty();
+   | |____^
+   |
+help: Check if the original Iterator has anything instead of collecting it and seeing if it's empty
+   |
+LL |     
+LL |     sample.iter().next().is_none();
+   |
+
+error: avoid using `collect()` when not needed
+  --> $DIR/needless_collect_indirect.rs:11:5
+   |
+LL | /     let indirect_contains = sample.iter().collect::<VecDeque<_>>();
+LL | |     indirect_contains.contains(&&5);
+   | |____^
+   |
+help: Check if the original Iterator contains an element instead of collecting then checking
+   |
+LL |     
+LL |     sample.iter().any(|x| x == &&5);
+   |
+
+error: aborting due to 4 previous errors
+
diff --git a/tests/ui/trait_duplication_in_bounds.rs b/tests/ui/trait_duplication_in_bounds.rs
new file mode 100644
index 00000000000..cb2b0054e35
--- /dev/null
+++ b/tests/ui/trait_duplication_in_bounds.rs
@@ -0,0 +1,31 @@
+#![deny(clippy::trait_duplication_in_bounds)]
+
+use std::ops::{Add, AddAssign, Div, DivAssign, Mul, MulAssign, Sub, SubAssign};
+
+fn bad_foo<T: Clone + Default, Z: Copy>(arg0: T, arg1: Z)
+where
+    T: Clone,
+    T: Default,
+{
+    unimplemented!();
+}
+
+fn good_bar<T: Clone + Default>(arg: T) {
+    unimplemented!();
+}
+
+fn good_foo<T>(arg: T)
+where
+    T: Clone + Default,
+{
+    unimplemented!();
+}
+
+fn good_foobar<T: Default>(arg: T)
+where
+    T: Clone,
+{
+    unimplemented!();
+}
+
+fn main() {}
diff --git a/tests/ui/trait_duplication_in_bounds.stderr b/tests/ui/trait_duplication_in_bounds.stderr
new file mode 100644
index 00000000000..027e1c75204
--- /dev/null
+++ b/tests/ui/trait_duplication_in_bounds.stderr
@@ -0,0 +1,23 @@
+error: this trait bound is already specified in the where clause
+  --> $DIR/trait_duplication_in_bounds.rs:5:15
+   |
+LL | fn bad_foo<T: Clone + Default, Z: Copy>(arg0: T, arg1: Z)
+   |               ^^^^^
+   |
+note: the lint level is defined here
+  --> $DIR/trait_duplication_in_bounds.rs:1:9
+   |
+LL | #![deny(clippy::trait_duplication_in_bounds)]
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   = help: consider removing this trait bound
+
+error: this trait bound is already specified in the where clause
+  --> $DIR/trait_duplication_in_bounds.rs:5:23
+   |
+LL | fn bad_foo<T: Clone + Default, Z: Copy>(arg0: T, arg1: Z)
+   |                       ^^^^^^^
+   |
+   = help: consider removing this trait bound
+
+error: aborting due to 2 previous errors
+