Auto merge of #7516 - lf-:unwrap-or-default, r=xFrednet

Add `unwrap_or_else_default` lint

---

*Please write a short comment explaining your change (or "none" for internal only changes)*

changelog: Add a new [`unwrap_or_else_default`] style lint. This will catch `unwrap_or_else(Default::default)` on Result and Option and suggest `unwrap_or_default()` instead.

5 files changed, 27 insertions, 8 deletions

diff --git a/clippy_utils/src/diagnostics.rs b/clippy_utils/src/diagnostics.rs
index 7c94474cb35..71cfa196fc3 100644
--- a/clippy_utils/src/diagnostics.rs
+++ b/clippy_utils/src/diagnostics.rs
@@ -65,7 +65,7 @@ pub fn span_lint<T: LintContext>(cx: &T, lint: &'static Lint, sp: impl Into<Mult
 ///
 /// # Example
 ///
-/// ```ignore
+/// ```text
 /// error: constant division of 0.0 with 0.0 will always result in NaN
 ///   --> $DIR/zero_div_zero.rs:6:25
 ///    |
@@ -103,7 +103,7 @@ pub fn span_lint_and_help<'a, T: LintContext>(
 ///
 /// # Example
 ///
-/// ```ignore
+/// ```text
 /// error: calls to `std::mem::forget` with a reference instead of an owned value. Forgetting a reference does nothing.
 ///   --> $DIR/drop_forget_ref.rs:10:5
 ///    |
@@ -189,7 +189,7 @@ pub fn span_lint_hir_and_then(
 ///
 /// # Example
 ///
-/// ```ignore
+/// ```text
 /// error: This `.fold` can be more succinctly expressed as `.any`
 /// --> $DIR/methods.rs:390:13
 ///     |
diff --git a/clippy_utils/src/higher.rs b/clippy_utils/src/higher.rs
index f32f1109b08..884180f0586 100644
--- a/clippy_utils/src/higher.rs
+++ b/clippy_utils/src/higher.rs
@@ -195,8 +195,8 @@ pub fn vec_macro<'e>(cx: &LateContext<'_>, expr: &'e hir::Expr<'_>) -> Option<Ve
 /// - `assert!`, `assert_eq!` and `assert_ne!`
 /// - `debug_assert!`, `debug_assert_eq!` and `debug_assert_ne!`
 /// For example:
-/// `assert!(expr)` will return Some([expr])
-/// `debug_assert_eq!(a, b)` will return Some([a, b])
+/// `assert!(expr)` will return `Some([expr])`
+/// `debug_assert_eq!(a, b)` will return `Some([a, b])`
 pub fn extract_assert_macro_args<'tcx>(e: &'tcx Expr<'tcx>) -> Option<Vec<&'tcx Expr<'tcx>>> {
     /// Try to match the AST for a pattern that contains a match, for example when two args are
     /// compared
@@ -283,7 +283,7 @@ pub struct FormatArgsExpn<'tcx> {
 
     /// String literal expressions which represent the format string split by "{}"
     pub format_string_parts: &'tcx [Expr<'tcx>],
-    /// Symbols corresponding to [`format_string_parts`]
+    /// Symbols corresponding to [`Self::format_string_parts`]
     pub format_string_symbols: Vec<Symbol>,
     /// Expressions like `ArgumentV1::new(arg0, Debug::fmt)`
     pub args: &'tcx [Expr<'tcx>],
diff --git a/clippy_utils/src/lib.rs b/clippy_utils/src/lib.rs
index e930338270c..1d59d6bfea1 100644
--- a/clippy_utils/src/lib.rs
+++ b/clippy_utils/src/lib.rs
@@ -326,6 +326,25 @@ pub fn is_trait_method(cx: &LateContext<'_>, expr: &Expr<'_>, diag_item: Symbol)
         .map_or(false, |did| is_diag_trait_item(cx, did, diag_item))
 }
 
+/// Checks if the given expression is a path referring an item on the trait
+/// that is marked with the given diagnostic item.
+///
+/// For checking method call expressions instead of path expressions, use
+/// [`is_trait_method`].
+///
+/// For example, this can be used to find if an expression like `u64::default`
+/// refers to an item of the trait `Default`, which is associated with the
+/// `diag_item` of `sym::Default`.
+pub fn is_trait_item(cx: &LateContext<'_>, expr: &Expr<'_>, diag_item: Symbol) -> bool {
+    if let hir::ExprKind::Path(ref qpath) = expr.kind {
+        cx.qpath_res(qpath, expr.hir_id)
+            .opt_def_id()
+            .map_or(false, |def_id| is_diag_trait_item(cx, def_id, diag_item))
+    } else {
+        false
+    }
+}
+
 pub fn last_path_segment<'tcx>(path: &QPath<'tcx>) -> &'tcx PathSegment<'tcx> {
     match *path {
         QPath::Resolved(_, path) => path.segments.last().expect("A path must have at least one segment"),
diff --git a/clippy_utils/src/source.rs b/clippy_utils/src/source.rs
index 4d49b43bde9..789079510c5 100644
--- a/clippy_utils/src/source.rs
+++ b/clippy_utils/src/source.rs
@@ -168,7 +168,7 @@ pub fn snippet<'a, T: LintContext>(cx: &T, span: Span, default: &'a str) -> Cow<
     snippet_opt(cx, span).map_or_else(|| Cow::Borrowed(default), From::from)
 }
 
-/// Same as `snippet`, but it adapts the applicability level by following rules:
+/// Same as [`snippet`], but it adapts the applicability level by following rules:
 ///
 /// - Applicability level `Unspecified` will never be changed.
 /// - If the span is inside a macro, change the applicability level to `MaybeIncorrect`.
diff --git a/clippy_utils/src/ty.rs b/clippy_utils/src/ty.rs
index e914dc1c222..4f9aaf396b8 100644
--- a/clippy_utils/src/ty.rs
+++ b/clippy_utils/src/ty.rs
@@ -114,7 +114,7 @@ pub fn has_iter_method(cx: &LateContext<'_>, probably_ref_ty: Ty<'_>) -> Option<
 
 /// Checks whether a type implements a trait.
 /// The function returns false in case the type contains an inference variable.
-/// See also `get_trait_def_id`.
+/// See also [`get_trait_def_id`](super::get_trait_def_id).
 pub fn implements_trait<'tcx>(
     cx: &LateContext<'tcx>,
     ty: Ty<'tcx>,