Split out the UNUSED_* lints into a new module

Part of #22206

3 files changed, 477 insertions, 445 deletions

diff --git a/src/librustc_lint/builtin.rs b/src/librustc_lint/builtin.rs
index fe835f274b6..febf8ef6e47 100644
--- a/src/librustc_lint/builtin.rs
+++ b/src/librustc_lint/builtin.rs
@@ -28,8 +28,8 @@
 //! Use the former for unit-like structs and the latter for structs with
 //! a `pub fn new()`.
 
-use metadata::{csearch, decoder};
-use middle::{cfg, def, infer, pat_util, stability, traits};
+use metadata::decoder;
+use middle::{cfg, def, infer, stability, traits};
 use middle::def_id::DefId;
 use middle::subst::Substs;
 use middle::ty::{self, Ty};
@@ -37,21 +37,19 @@ use middle::ty::adjustment;
 use middle::const_eval::{eval_const_expr_partial, ConstVal};
 use middle::const_eval::EvalHint::ExprTypeChecked;
 use rustc::front::map as hir_map;
-use util::nodemap::{FnvHashMap, FnvHashSet, NodeSet};
-use lint::{Level, LateContext, EarlyContext, LintContext, LintArray, Lint};
-use lint::{LintPass, EarlyLintPass, LateLintPass};
+use util::nodemap::{FnvHashSet, NodeSet};
+use lint::{Level, LateContext, LintContext, LintArray, Lint};
+use lint::{LintPass, LateLintPass};
 
 use std::collections::HashSet;
-use std::collections::hash_map::Entry::{Occupied, Vacant};
-use std::{cmp, slice};
+use std::cmp;
 use std::{i8, i16, i32, i64, u8, u16, u32, u64, f32, f64};
 
 use syntax::{abi, ast};
 use syntax::attr::{self, AttrMetaMethods};
 use syntax::codemap::{self, Span};
-use syntax::feature_gate::{KNOWN_ATTRIBUTES, AttributeType, emit_feature_err, GateIssue};
+use syntax::feature_gate::{emit_feature_err, GateIssue};
 use syntax::ast::{TyIs, TyUs, TyI8, TyU8, TyI16, TyU16, TyI32, TyU32, TyI64, TyU64};
-use syntax::ptr::P;
 
 use rustc_front::hir;
 use rustc_front::visit::{self, FnKind, Visitor};
@@ -884,302 +882,6 @@ impl LateLintPass for RawPointerDerive {
 }
 
 declare_lint! {
-    UNUSED_ATTRIBUTES,
-    Warn,
-    "detects attributes that were not used by the compiler"
-}
-
-#[derive(Copy, Clone)]
-pub struct UnusedAttributes;
-
-impl LintPass for UnusedAttributes {
-    fn get_lints(&self) -> LintArray {
-        lint_array!(UNUSED_ATTRIBUTES)
-    }
-}
-
-impl LateLintPass for UnusedAttributes {
-    fn check_attribute(&mut self, cx: &LateContext, attr: &ast::Attribute) {
-        // Note that check_name() marks the attribute as used if it matches.
-        for &(ref name, ty, _) in KNOWN_ATTRIBUTES {
-            match ty {
-                AttributeType::Whitelisted if attr.check_name(name) => {
-                    break;
-                },
-                _ => ()
-            }
-        }
-
-        let plugin_attributes = cx.sess().plugin_attributes.borrow_mut();
-        for &(ref name, ty) in plugin_attributes.iter() {
-            if ty == AttributeType::Whitelisted && attr.check_name(&*name) {
-                break;
-            }
-        }
-
-        if !attr::is_used(attr) {
-            cx.span_lint(UNUSED_ATTRIBUTES, attr.span, "unused attribute");
-            // Is it a builtin attribute that must be used at the crate level?
-            let known_crate = KNOWN_ATTRIBUTES.iter().find(|&&(name, ty, _)| {
-                attr.name() == name &&
-                ty == AttributeType::CrateLevel
-            }).is_some();
-
-            // Has a plugin registered this attribute as one which must be used at
-            // the crate level?
-            let plugin_crate = plugin_attributes.iter()
-                                                .find(|&&(ref x, t)| {
-                                                        &*attr.name() == &*x &&
-                                                        AttributeType::CrateLevel == t
-                                                    }).is_some();
-            if  known_crate || plugin_crate {
-                let msg = match attr.node.style {
-                    ast::AttrOuter => "crate-level attribute should be an inner \
-                                       attribute: add an exclamation mark: #![foo]",
-                    ast::AttrInner => "crate-level attribute should be in the \
-                                       root module",
-                };
-                cx.span_lint(UNUSED_ATTRIBUTES, attr.span, msg);
-            }
-        }
-    }
-}
-
-declare_lint! {
-    pub PATH_STATEMENTS,
-    Warn,
-    "path statements with no effect"
-}
-
-#[derive(Copy, Clone)]
-pub struct PathStatements;
-
-impl LintPass for PathStatements {
-    fn get_lints(&self) -> LintArray {
-        lint_array!(PATH_STATEMENTS)
-    }
-}
-
-impl LateLintPass for PathStatements {
-    fn check_stmt(&mut self, cx: &LateContext, s: &hir::Stmt) {
-        match s.node {
-            hir::StmtSemi(ref expr, _) => {
-                match expr.node {
-                    hir::ExprPath(..) => cx.span_lint(PATH_STATEMENTS, s.span,
-                                                      "path statement with no effect"),
-                    _ => ()
-                }
-            }
-            _ => ()
-        }
-    }
-}
-
-declare_lint! {
-    pub UNUSED_MUST_USE,
-    Warn,
-    "unused result of a type flagged as #[must_use]"
-}
-
-declare_lint! {
-    pub UNUSED_RESULTS,
-    Allow,
-    "unused result of an expression in a statement"
-}
-
-#[derive(Copy, Clone)]
-pub struct UnusedResults;
-
-impl LintPass for UnusedResults {
-    fn get_lints(&self) -> LintArray {
-        lint_array!(UNUSED_MUST_USE, UNUSED_RESULTS)
-    }
-}
-
-impl LateLintPass for UnusedResults {
-    fn check_stmt(&mut self, cx: &LateContext, s: &hir::Stmt) {
-        let expr = match s.node {
-            hir::StmtSemi(ref expr, _) => &**expr,
-            _ => return
-        };
-
-        if let hir::ExprRet(..) = expr.node {
-            return;
-        }
-
-        let t = cx.tcx.expr_ty(&expr);
-        let warned = match t.sty {
-            ty::TyTuple(ref tys) if tys.is_empty() => return,
-            ty::TyBool => return,
-            ty::TyStruct(def, _) |
-            ty::TyEnum(def, _) => {
-                if def.did.is_local() {
-                    if let hir_map::NodeItem(it) = cx.tcx.map.get(def.did.node) {
-                        check_must_use(cx, &it.attrs, s.span)
-                    } else {
-                        false
-                    }
-                } else {
-                    let attrs = csearch::get_item_attrs(&cx.sess().cstore, def.did);
-                    check_must_use(cx, &attrs[..], s.span)
-                }
-            }
-            _ => false,
-        };
-        if !warned {
-            cx.span_lint(UNUSED_RESULTS, s.span, "unused result");
-        }
-
-        fn check_must_use(cx: &LateContext, attrs: &[ast::Attribute], sp: Span) -> bool {
-            for attr in attrs {
-                if attr.check_name("must_use") {
-                    let mut msg = "unused result which must be used".to_string();
-                    // check for #[must_use="..."]
-                    match attr.value_str() {
-                        None => {}
-                        Some(s) => {
-                            msg.push_str(": ");
-                            msg.push_str(&s);
-                        }
-                    }
-                    cx.span_lint(UNUSED_MUST_USE, sp, &msg);
-                    return true;
-                }
-            }
-            false
-        }
-    }
-}
-
-declare_lint! {
-    UNUSED_PARENS,
-    Warn,
-    "`if`, `match`, `while` and `return` do not need parentheses"
-}
-
-#[derive(Copy, Clone)]
-pub struct UnusedParens;
-
-impl UnusedParens {
-    fn check_unused_parens_core(&self, cx: &EarlyContext, value: &ast::Expr, msg: &str,
-                                struct_lit_needs_parens: bool) {
-        if let ast::ExprParen(ref inner) = value.node {
-            let necessary = struct_lit_needs_parens && contains_exterior_struct_lit(&**inner);
-            if !necessary {
-                cx.span_lint(UNUSED_PARENS, value.span,
-                             &format!("unnecessary parentheses around {}", msg))
-            }
-        }
-
-        /// Expressions that syntactically contain an "exterior" struct
-        /// literal i.e. not surrounded by any parens or other
-        /// delimiters, e.g. `X { y: 1 }`, `X { y: 1 }.method()`, `foo
-        /// == X { y: 1 }` and `X { y: 1 } == foo` all do, but `(X {
-        /// y: 1 }) == foo` does not.
-        fn contains_exterior_struct_lit(value: &ast::Expr) -> bool {
-            match value.node {
-                ast::ExprStruct(..) => true,
-
-                ast::ExprAssign(ref lhs, ref rhs) |
-                ast::ExprAssignOp(_, ref lhs, ref rhs) |
-                ast::ExprBinary(_, ref lhs, ref rhs) => {
-                    // X { y: 1 } + X { y: 2 }
-                    contains_exterior_struct_lit(&**lhs) ||
-                        contains_exterior_struct_lit(&**rhs)
-                }
-                ast::ExprUnary(_, ref x) |
-                ast::ExprCast(ref x, _) |
-                ast::ExprField(ref x, _) |
-                ast::ExprTupField(ref x, _) |
-                ast::ExprIndex(ref x, _) => {
-                    // &X { y: 1 }, X { y: 1 }.y
-                    contains_exterior_struct_lit(&**x)
-                }
-
-                ast::ExprMethodCall(_, _, ref exprs) => {
-                    // X { y: 1 }.bar(...)
-                    contains_exterior_struct_lit(&*exprs[0])
-                }
-
-                _ => false
-            }
-        }
-    }
-}
-
-impl LintPass for UnusedParens {
-    fn get_lints(&self) -> LintArray {
-        lint_array!(UNUSED_PARENS)
-    }
-}
-
-impl EarlyLintPass for UnusedParens {
-    fn check_expr(&mut self, cx: &EarlyContext, e: &ast::Expr) {
-        let (value, msg, struct_lit_needs_parens) = match e.node {
-            ast::ExprIf(ref cond, _, _) => (cond, "`if` condition", true),
-            ast::ExprWhile(ref cond, _, _) => (cond, "`while` condition", true),
-            ast::ExprMatch(ref head, _, source) => match source {
-                ast::MatchSource::Normal => (head, "`match` head expression", true),
-                ast::MatchSource::IfLetDesugar { .. } => (head, "`if let` head expression", true),
-                ast::MatchSource::WhileLetDesugar => (head, "`while let` head expression", true),
-                ast::MatchSource::ForLoopDesugar => (head, "`for` head expression", true),
-            },
-            ast::ExprRet(Some(ref value)) => (value, "`return` value", false),
-            ast::ExprAssign(_, ref value) => (value, "assigned value", false),
-            ast::ExprAssignOp(_, _, ref value) => (value, "assigned value", false),
-            _ => return
-        };
-        self.check_unused_parens_core(cx, &**value, msg, struct_lit_needs_parens);
-    }
-
-    fn check_stmt(&mut self, cx: &EarlyContext, s: &ast::Stmt) {
-        let (value, msg) = match s.node {
-            ast::StmtDecl(ref decl, _) => match decl.node {
-                ast::DeclLocal(ref local) => match local.init {
-                    Some(ref value) => (value, "assigned value"),
-                    None => return
-                },
-                _ => return
-            },
-            _ => return
-        };
-        self.check_unused_parens_core(cx, &**value, msg, false);
-    }
-}
-
-declare_lint! {
-    UNUSED_IMPORT_BRACES,
-    Allow,
-    "unnecessary braces around an imported item"
-}
-
-#[derive(Copy, Clone)]
-pub struct UnusedImportBraces;
-
-impl LintPass for UnusedImportBraces {
-    fn get_lints(&self) -> LintArray {
-        lint_array!(UNUSED_IMPORT_BRACES)
-    }
-}
-
-impl LateLintPass for UnusedImportBraces {
-    fn check_item(&mut self, cx: &LateContext, item: &hir::Item) {
-        if let hir::ItemUse(ref view_path) = item.node {
-            if let hir::ViewPathList(_, ref items) = view_path.node {
-                if items.len() == 1 {
-                    if let hir::PathListIdent {ref name, ..} = items[0].node {
-                        let m = format!("braces around {} is unnecessary",
-                                        name);
-                        cx.span_lint(UNUSED_IMPORT_BRACES, item.span,
-                                     &m[..]);
-                    }
-                }
-            }
-        }
-    }
-}
-
-declare_lint! {
     NON_SHORTHAND_FIELD_PATTERNS,
     Warn,
     "using `Struct { x: x }` instead of `Struct { x }`"
@@ -1221,33 +923,6 @@ impl LateLintPass for NonShorthandFieldPatterns {
 }
 
 declare_lint! {
-    pub UNUSED_UNSAFE,
-    Warn,
-    "unnecessary use of an `unsafe` block"
-}
-
-#[derive(Copy, Clone)]
-pub struct UnusedUnsafe;
-
-impl LintPass for UnusedUnsafe {
-    fn get_lints(&self) -> LintArray {
-        lint_array!(UNUSED_UNSAFE)
-    }
-}
-
-impl LateLintPass for UnusedUnsafe {
-    fn check_expr(&mut self, cx: &LateContext, e: &hir::Expr) {
-        if let hir::ExprBlock(ref blk) = e.node {
-            // Don't warn about generated blocks, that'll just pollute the output.
-            if blk.rules == hir::UnsafeBlock(hir::UserProvided) &&
-                !cx.tcx.used_unsafe.borrow().contains(&blk.id) {
-                    cx.span_lint(UNUSED_UNSAFE, blk.span, "unnecessary `unsafe` block");
-            }
-        }
-    }
-}
-
-declare_lint! {
     UNSAFE_CODE,
     Allow,
     "usage of `unsafe` code"
@@ -1311,119 +986,6 @@ impl LateLintPass for UnsafeCode {
 }
 
 declare_lint! {
-    pub UNUSED_MUT,
-    Warn,
-    "detect mut variables which don't need to be mutable"
-}
-
-#[derive(Copy, Clone)]
-pub struct UnusedMut;
-
-impl UnusedMut {
-    fn check_unused_mut_pat(&self, cx: &LateContext, pats: &[P<hir::Pat>]) {
-        // collect all mutable pattern and group their NodeIDs by their Identifier to
-        // avoid false warnings in match arms with multiple patterns
-
-        let mut mutables = FnvHashMap();
-        for p in pats {
-            pat_util::pat_bindings(&cx.tcx.def_map, p, |mode, id, _, path1| {
-                let ident = path1.node;
-                if let hir::BindByValue(hir::MutMutable) = mode {
-                    if !ident.name.as_str().starts_with("_") {
-                        match mutables.entry(ident.name.usize()) {
-                            Vacant(entry) => { entry.insert(vec![id]); },
-                            Occupied(mut entry) => { entry.get_mut().push(id); },
-                        }
-                    }
-                }
-            });
-        }
-
-        let used_mutables = cx.tcx.used_mut_nodes.borrow();
-        for (_, v) in &mutables {
-            if !v.iter().any(|e| used_mutables.contains(e)) {
-                cx.span_lint(UNUSED_MUT, cx.tcx.map.span(v[0]),
-                             "variable does not need to be mutable");
-            }
-        }
-    }
-}
-
-impl LintPass for UnusedMut {
-    fn get_lints(&self) -> LintArray {
-        lint_array!(UNUSED_MUT)
-    }
-}
-
-impl LateLintPass for UnusedMut {
-    fn check_expr(&mut self, cx: &LateContext, e: &hir::Expr) {
-        if let hir::ExprMatch(_, ref arms, _) = e.node {
-            for a in arms {
-                self.check_unused_mut_pat(cx, &a.pats)
-            }
-        }
-    }
-
-    fn check_stmt(&mut self, cx: &LateContext, s: &hir::Stmt) {
-        if let hir::StmtDecl(ref d, _) = s.node {
-            if let hir::DeclLocal(ref l) = d.node {
-                self.check_unused_mut_pat(cx, slice::ref_slice(&l.pat));
-            }
-        }
-    }
-
-    fn check_fn(&mut self, cx: &LateContext,
-                _: FnKind, decl: &hir::FnDecl,
-                _: &hir::Block, _: Span, _: ast::NodeId) {
-        for a in &decl.inputs {
-            self.check_unused_mut_pat(cx, slice::ref_slice(&a.pat));
-        }
-    }
-}
-
-declare_lint! {
-    UNUSED_ALLOCATION,
-    Warn,
-    "detects unnecessary allocations that can be eliminated"
-}
-
-#[derive(Copy, Clone)]
-pub struct UnusedAllocation;
-
-impl LintPass for UnusedAllocation {
-    fn get_lints(&self) -> LintArray {
-        lint_array!(UNUSED_ALLOCATION)
-    }
-}
-
-impl LateLintPass for UnusedAllocation {
-    fn check_expr(&mut self, cx: &LateContext, e: &hir::Expr) {
-        match e.node {
-            hir::ExprUnary(hir::UnUniq, _) => (),
-            _ => return
-        }
-
-        if let Some(adjustment) = cx.tcx.tables.borrow().adjustments.get(&e.id) {
-            if let adjustment::AdjustDerefRef(adjustment::AutoDerefRef {
-                ref autoref, ..
-            }) = *adjustment {
-                match autoref {
-                    &Some(adjustment::AutoPtr(_, hir::MutImmutable)) => {
-                        cx.span_lint(UNUSED_ALLOCATION, e.span,
-                                     "unnecessary allocation, use & instead");
-                    }
-                    &Some(adjustment::AutoPtr(_, hir::MutMutable)) => {
-                        cx.span_lint(UNUSED_ALLOCATION, e.span,
-                                     "unnecessary allocation, use &mut instead");
-                    }
-                    _ => ()
-                }
-            }
-        }
-    }
-}
-
-declare_lint! {
     MISSING_DOCS,
     Allow,
     "detects missing documentation for public members"
diff --git a/src/librustc_lint/lib.rs b/src/librustc_lint/lib.rs
index a05abbb3fab..674631cd3a5 100644
--- a/src/librustc_lint/lib.rs
+++ b/src/librustc_lint/lib.rs
@@ -60,9 +60,11 @@ use lint::LintId;
 
 mod bad_style;
 mod builtin;
+mod unused;
 
 use bad_style::*;
 use builtin::*;
+use unused::*;
 
 /// Tell the `LintStore` about all the built-in lints (the ones
 /// defined in this crate and the ones defined in
diff --git a/src/librustc_lint/unused.rs b/src/librustc_lint/unused.rs
new file mode 100644
index 00000000000..6df32f53d81
--- /dev/null
+++ b/src/librustc_lint/unused.rs
@@ -0,0 +1,468 @@
+// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+use metadata::csearch;
+use middle::pat_util;
+use middle::ty;
+use middle::ty::adjustment;
+use rustc::front::map as hir_map;
+use util::nodemap::FnvHashMap;
+use lint::{LateContext, EarlyContext, LintContext, LintArray};
+use lint::{LintPass, EarlyLintPass, LateLintPass};
+
+use std::collections::hash_map::Entry::{Occupied, Vacant};
+use std::slice;
+
+use syntax::ast;
+use syntax::attr::{self, AttrMetaMethods};
+use syntax::codemap::Span;
+use syntax::feature_gate::{KNOWN_ATTRIBUTES, AttributeType};
+use syntax::ptr::P;
+
+use rustc_front::hir;
+
+use rustc_front::visit::FnKind;
+
+declare_lint! {
+    pub UNUSED_MUT,
+    Warn,
+    "detect mut variables which don't need to be mutable"
+}
+
+#[derive(Copy, Clone)]
+pub struct UnusedMut;
+
+impl UnusedMut {
+    fn check_unused_mut_pat(&self, cx: &LateContext, pats: &[P<hir::Pat>]) {
+        // collect all mutable pattern and group their NodeIDs by their Identifier to
+        // avoid false warnings in match arms with multiple patterns
+
+        let mut mutables = FnvHashMap();
+        for p in pats {
+            pat_util::pat_bindings(&cx.tcx.def_map, p, |mode, id, _, path1| {
+                let ident = path1.node;
+                if let hir::BindByValue(hir::MutMutable) = mode {
+                    if !ident.name.as_str().starts_with("_") {
+                        match mutables.entry(ident.name.usize()) {
+                            Vacant(entry) => { entry.insert(vec![id]); },
+                            Occupied(mut entry) => { entry.get_mut().push(id); },
+                        }
+                    }
+                }
+            });
+        }
+
+        let used_mutables = cx.tcx.used_mut_nodes.borrow();
+        for (_, v) in &mutables {
+            if !v.iter().any(|e| used_mutables.contains(e)) {
+                cx.span_lint(UNUSED_MUT, cx.tcx.map.span(v[0]),
+                             "variable does not need to be mutable");
+            }
+        }
+    }
+}
+
+impl LintPass for UnusedMut {
+    fn get_lints(&self) -> LintArray {
+        lint_array!(UNUSED_MUT)
+    }
+}
+
+impl LateLintPass for UnusedMut {
+    fn check_expr(&mut self, cx: &LateContext, e: &hir::Expr) {
+        if let hir::ExprMatch(_, ref arms, _) = e.node {
+            for a in arms {
+                self.check_unused_mut_pat(cx, &a.pats)
+            }
+        }
+    }
+
+    fn check_stmt(&mut self, cx: &LateContext, s: &hir::Stmt) {
+        if let hir::StmtDecl(ref d, _) = s.node {
+            if let hir::DeclLocal(ref l) = d.node {
+                self.check_unused_mut_pat(cx, slice::ref_slice(&l.pat));
+            }
+        }
+    }
+
+    fn check_fn(&mut self, cx: &LateContext,
+                _: FnKind, decl: &hir::FnDecl,
+                _: &hir::Block, _: Span, _: ast::NodeId) {
+        for a in &decl.inputs {
+            self.check_unused_mut_pat(cx, slice::ref_slice(&a.pat));
+        }
+    }
+}
+
+declare_lint! {
+    pub UNUSED_MUST_USE,
+    Warn,
+    "unused result of a type flagged as #[must_use]"
+}
+
+declare_lint! {
+    pub UNUSED_RESULTS,
+    Allow,
+    "unused result of an expression in a statement"
+}
+
+#[derive(Copy, Clone)]
+pub struct UnusedResults;
+
+impl LintPass for UnusedResults {
+    fn get_lints(&self) -> LintArray {
+        lint_array!(UNUSED_MUST_USE, UNUSED_RESULTS)
+    }
+}
+
+impl LateLintPass for UnusedResults {
+    fn check_stmt(&mut self, cx: &LateContext, s: &hir::Stmt) {
+        let expr = match s.node {
+            hir::StmtSemi(ref expr, _) => &**expr,
+            _ => return
+        };
+
+        if let hir::ExprRet(..) = expr.node {
+            return;
+        }
+
+        let t = cx.tcx.expr_ty(&expr);
+        let warned = match t.sty {
+            ty::TyTuple(ref tys) if tys.is_empty() => return,
+            ty::TyBool => return,
+            ty::TyStruct(def, _) |
+            ty::TyEnum(def, _) => {
+                if def.did.is_local() {
+                    if let hir_map::NodeItem(it) = cx.tcx.map.get(def.did.node) {
+                        check_must_use(cx, &it.attrs, s.span)
+                    } else {
+                        false
+                    }
+                } else {
+                    let attrs = csearch::get_item_attrs(&cx.sess().cstore, def.did);
+                    check_must_use(cx, &attrs[..], s.span)
+                }
+            }
+            _ => false,
+        };
+        if !warned {
+            cx.span_lint(UNUSED_RESULTS, s.span, "unused result");
+        }
+
+        fn check_must_use(cx: &LateContext, attrs: &[ast::Attribute], sp: Span) -> bool {
+            for attr in attrs {
+                if attr.check_name("must_use") {
+                    let mut msg = "unused result which must be used".to_string();
+                    // check for #[must_use="..."]
+                    match attr.value_str() {
+                        None => {}
+                        Some(s) => {
+                            msg.push_str(": ");
+                            msg.push_str(&s);
+                        }
+                    }
+                    cx.span_lint(UNUSED_MUST_USE, sp, &msg);
+                    return true;
+                }
+            }
+            false
+        }
+    }
+}
+
+declare_lint! {
+    pub UNUSED_UNSAFE,
+    Warn,
+    "unnecessary use of an `unsafe` block"
+}
+
+#[derive(Copy, Clone)]
+pub struct UnusedUnsafe;
+
+impl LintPass for UnusedUnsafe {
+    fn get_lints(&self) -> LintArray {
+        lint_array!(UNUSED_UNSAFE)
+    }
+}
+
+impl LateLintPass for UnusedUnsafe {
+    fn check_expr(&mut self, cx: &LateContext, e: &hir::Expr) {
+        if let hir::ExprBlock(ref blk) = e.node {
+            // Don't warn about generated blocks, that'll just pollute the output.
+            if blk.rules == hir::UnsafeBlock(hir::UserProvided) &&
+                !cx.tcx.used_unsafe.borrow().contains(&blk.id) {
+                    cx.span_lint(UNUSED_UNSAFE, blk.span, "unnecessary `unsafe` block");
+            }
+        }
+    }
+}
+
+declare_lint! {
+    pub PATH_STATEMENTS,
+    Warn,
+    "path statements with no effect"
+}
+
+#[derive(Copy, Clone)]
+pub struct PathStatements;
+
+impl LintPass for PathStatements {
+    fn get_lints(&self) -> LintArray {
+        lint_array!(PATH_STATEMENTS)
+    }
+}
+
+impl LateLintPass for PathStatements {
+    fn check_stmt(&mut self, cx: &LateContext, s: &hir::Stmt) {
+        match s.node {
+            hir::StmtSemi(ref expr, _) => {
+                match expr.node {
+                    hir::ExprPath(..) => cx.span_lint(PATH_STATEMENTS, s.span,
+                                                      "path statement with no effect"),
+                    _ => ()
+                }
+            }
+            _ => ()
+        }
+    }
+}
+
+declare_lint! {
+    UNUSED_ATTRIBUTES,
+    Warn,
+    "detects attributes that were not used by the compiler"
+}
+
+#[derive(Copy, Clone)]
+pub struct UnusedAttributes;
+
+impl LintPass for UnusedAttributes {
+    fn get_lints(&self) -> LintArray {
+        lint_array!(UNUSED_ATTRIBUTES)
+    }
+}
+
+impl LateLintPass for UnusedAttributes {
+    fn check_attribute(&mut self, cx: &LateContext, attr: &ast::Attribute) {
+        // Note that check_name() marks the attribute as used if it matches.
+        for &(ref name, ty, _) in KNOWN_ATTRIBUTES {
+            match ty {
+                AttributeType::Whitelisted if attr.check_name(name) => {
+                    break;
+                },
+                _ => ()
+            }
+        }
+
+        let plugin_attributes = cx.sess().plugin_attributes.borrow_mut();
+        for &(ref name, ty) in plugin_attributes.iter() {
+            if ty == AttributeType::Whitelisted && attr.check_name(&*name) {
+                break;
+            }
+        }
+
+        if !attr::is_used(attr) {
+            cx.span_lint(UNUSED_ATTRIBUTES, attr.span, "unused attribute");
+            // Is it a builtin attribute that must be used at the crate level?
+            let known_crate = KNOWN_ATTRIBUTES.iter().find(|&&(name, ty, _)| {
+                attr.name() == name &&
+                ty == AttributeType::CrateLevel
+            }).is_some();
+
+            // Has a plugin registered this attribute as one which must be used at
+            // the crate level?
+            let plugin_crate = plugin_attributes.iter()
+                                                .find(|&&(ref x, t)| {
+                                                        &*attr.name() == &*x &&
+                                                        AttributeType::CrateLevel == t
+                                                    }).is_some();
+            if  known_crate || plugin_crate {
+                let msg = match attr.node.style {
+                    ast::AttrOuter => "crate-level attribute should be an inner \
+                                       attribute: add an exclamation mark: #![foo]",
+                    ast::AttrInner => "crate-level attribute should be in the \
+                                       root module",
+                };
+                cx.span_lint(UNUSED_ATTRIBUTES, attr.span, msg);
+            }
+        }
+    }
+}
+
+declare_lint! {
+    UNUSED_PARENS,
+    Warn,
+    "`if`, `match`, `while` and `return` do not need parentheses"
+}
+
+#[derive(Copy, Clone)]
+pub struct UnusedParens;
+
+impl UnusedParens {
+    fn check_unused_parens_core(&self, cx: &EarlyContext, value: &ast::Expr, msg: &str,
+                                struct_lit_needs_parens: bool) {
+        if let ast::ExprParen(ref inner) = value.node {
+            let necessary = struct_lit_needs_parens && contains_exterior_struct_lit(&**inner);
+            if !necessary {
+                cx.span_lint(UNUSED_PARENS, value.span,
+                             &format!("unnecessary parentheses around {}", msg))
+            }
+        }
+
+        /// Expressions that syntactically contain an "exterior" struct
+        /// literal i.e. not surrounded by any parens or other
+        /// delimiters, e.g. `X { y: 1 }`, `X { y: 1 }.method()`, `foo
+        /// == X { y: 1 }` and `X { y: 1 } == foo` all do, but `(X {
+        /// y: 1 }) == foo` does not.
+        fn contains_exterior_struct_lit(value: &ast::Expr) -> bool {
+            match value.node {
+                ast::ExprStruct(..) => true,
+
+                ast::ExprAssign(ref lhs, ref rhs) |
+                ast::ExprAssignOp(_, ref lhs, ref rhs) |
+                ast::ExprBinary(_, ref lhs, ref rhs) => {
+                    // X { y: 1 } + X { y: 2 }
+                    contains_exterior_struct_lit(&**lhs) ||
+                        contains_exterior_struct_lit(&**rhs)
+                }
+                ast::ExprUnary(_, ref x) |
+                ast::ExprCast(ref x, _) |
+                ast::ExprField(ref x, _) |
+                ast::ExprTupField(ref x, _) |
+                ast::ExprIndex(ref x, _) => {
+                    // &X { y: 1 }, X { y: 1 }.y
+                    contains_exterior_struct_lit(&**x)
+                }
+
+                ast::ExprMethodCall(_, _, ref exprs) => {
+                    // X { y: 1 }.bar(...)
+                    contains_exterior_struct_lit(&*exprs[0])
+                }
+
+                _ => false
+            }
+        }
+    }
+}
+
+impl LintPass for UnusedParens {
+    fn get_lints(&self) -> LintArray {
+        lint_array!(UNUSED_PARENS)
+    }
+}
+
+impl EarlyLintPass for UnusedParens {
+    fn check_expr(&mut self, cx: &EarlyContext, e: &ast::Expr) {
+        let (value, msg, struct_lit_needs_parens) = match e.node {
+            ast::ExprIf(ref cond, _, _) => (cond, "`if` condition", true),
+            ast::ExprWhile(ref cond, _, _) => (cond, "`while` condition", true),
+            ast::ExprMatch(ref head, _, source) => match source {
+                ast::MatchSource::Normal => (head, "`match` head expression", true),
+                ast::MatchSource::IfLetDesugar { .. } => (head, "`if let` head expression", true),
+                ast::MatchSource::WhileLetDesugar => (head, "`while let` head expression", true),
+                ast::MatchSource::ForLoopDesugar => (head, "`for` head expression", true),
+            },
+            ast::ExprRet(Some(ref value)) => (value, "`return` value", false),
+            ast::ExprAssign(_, ref value) => (value, "assigned value", false),
+            ast::ExprAssignOp(_, _, ref value) => (value, "assigned value", false),
+            _ => return
+        };
+        self.check_unused_parens_core(cx, &**value, msg, struct_lit_needs_parens);
+    }
+
+    fn check_stmt(&mut self, cx: &EarlyContext, s: &ast::Stmt) {
+        let (value, msg) = match s.node {
+            ast::StmtDecl(ref decl, _) => match decl.node {
+                ast::DeclLocal(ref local) => match local.init {
+                    Some(ref value) => (value, "assigned value"),
+                    None => return
+                },
+                _ => return
+            },
+            _ => return
+        };
+        self.check_unused_parens_core(cx, &**value, msg, false);
+    }
+}
+
+declare_lint! {
+    UNUSED_IMPORT_BRACES,
+    Allow,
+    "unnecessary braces around an imported item"
+}
+
+#[derive(Copy, Clone)]
+pub struct UnusedImportBraces;
+
+impl LintPass for UnusedImportBraces {
+    fn get_lints(&self) -> LintArray {
+        lint_array!(UNUSED_IMPORT_BRACES)
+    }
+}
+
+impl LateLintPass for UnusedImportBraces {
+    fn check_item(&mut self, cx: &LateContext, item: &hir::Item) {
+        if let hir::ItemUse(ref view_path) = item.node {
+            if let hir::ViewPathList(_, ref items) = view_path.node {
+                if items.len() == 1 {
+                    if let hir::PathListIdent {ref name, ..} = items[0].node {
+                        let m = format!("braces around {} is unnecessary",
+                                        name);
+                        cx.span_lint(UNUSED_IMPORT_BRACES, item.span,
+                                     &m[..]);
+                    }
+                }
+            }
+        }
+    }
+}
+
+declare_lint! {
+    UNUSED_ALLOCATION,
+    Warn,
+    "detects unnecessary allocations that can be eliminated"
+}
+
+#[derive(Copy, Clone)]
+pub struct UnusedAllocation;
+
+impl LintPass for UnusedAllocation {
+    fn get_lints(&self) -> LintArray {
+        lint_array!(UNUSED_ALLOCATION)
+    }
+}
+
+impl LateLintPass for UnusedAllocation {
+    fn check_expr(&mut self, cx: &LateContext, e: &hir::Expr) {
+        match e.node {
+            hir::ExprUnary(hir::UnUniq, _) => (),
+            _ => return
+        }
+
+        if let Some(adjustment) = cx.tcx.tables.borrow().adjustments.get(&e.id) {
+            if let adjustment::AdjustDerefRef(adjustment::AutoDerefRef {
+                ref autoref, ..
+            }) = *adjustment {
+                match autoref {
+                    &Some(adjustment::AutoPtr(_, hir::MutImmutable)) => {
+                        cx.span_lint(UNUSED_ALLOCATION, e.span,
+                                     "unnecessary allocation, use & instead");
+                    }
+                    &Some(adjustment::AutoPtr(_, hir::MutMutable)) => {
+                        cx.span_lint(UNUSED_ALLOCATION, e.span,
+                                     "unnecessary allocation, use &mut instead");
+                    }
+                    _ => ()
+                }
+            }
+        }
+    }
+}
+