Auto merge of rust-lang#10120 - smoelius:or_insert_with, r=blyxyas

`unwrap_or_else_default` -> `unwrap_or_default` and improve resulting lint

Resolves rust-lang#10080 (though it doesn't implement exactly what's described there)

This PR does the following:
1. Merges `unwrap_or_else_default.rs`'s code into `or_fun_call.rs`
2. Extracts the code to handle `unwrap_or(/* default value */)` and similar, and moves it into `unwrap_or_else_default`
3. Implements the missing functionality from rust-lang#9342, e.g.,, to handle `or_insert_with(Default::default)`
4. Renames `unwrap_or_else_default` to `unwrap_or_default` (since the "new" lint handles both `unwrap_or` and `unwrap_or_else`, it seemed sensible to use the shortened name)

This PR is currently two commits. The first implements 1-3, the second implements 4.

A word about 2: the `or_fun_call` lint currently produces warnings like the following:
```
error: use of `unwrap_or` followed by a call to `new`
  --> $DIR/or_fun_call.rs:56:14
   |
LL |     with_new.unwrap_or(Vec::new());
   |              ^^^^^^^^^^^^^^^^^^^^^ help: try: `unwrap_or_default()`
```
To me, such warnings look like they should come from `unwrap_or_else_default`, not `or_fun_call`, especially since `or_fun_call` is [in the nursery](rust-lang/rust-clippy#9829).

---

changelog: Move: Renamed `unwrap_or_else_default` to [`unwrap_or_default`]
[rust-lang#10120](rust-lang/rust-clippy#10120)
changelog: Enhancement: [`unwrap_or_default`]: Now handles more functions, like `or_insert_with`
[rust-lang#10120](rust-lang/rust-clippy#10120)
<!-- changelog_checked-->

Author: bors

CHANGELOG.md

@@ -5370,6 +5370,7 @@ Released 2018-09-13
 [`unused_unit`]: https://rust-lang.github.io/rust-clippy/master/index.html#unused_unit
 [`unusual_byte_groupings`]: https://rust-lang.github.io/rust-clippy/master/index.html#unusual_byte_groupings
 [`unwrap_in_result`]: https://rust-lang.github.io/rust-clippy/master/index.html#unwrap_in_result
+[`unwrap_or_default`]: https://rust-lang.github.io/rust-clippy/master/index.html#unwrap_or_default
 [`unwrap_or_else_default`]: https://rust-lang.github.io/rust-clippy/master/index.html#unwrap_or_else_default
 [`unwrap_used`]: https://rust-lang.github.io/rust-clippy/master/index.html#unwrap_used
 [`upper_case_acronyms`]: https://rust-lang.github.io/rust-clippy/master/index.html#upper_case_acronyms

clippy_lints/src/declared_lints.rs

@@ -425,7 +425,7 @@ pub(crate) static LINTS: &[&crate::LintInfo] = &[
     crate::methods::UNNECESSARY_LITERAL_UNWRAP_INFO,
     crate::methods::UNNECESSARY_SORT_BY_INFO,
     crate::methods::UNNECESSARY_TO_OWNED_INFO,
-    crate::methods::UNWRAP_OR_ELSE_DEFAULT_INFO,
+    crate::methods::UNWRAP_OR_DEFAULT_INFO,
     crate::methods::UNWRAP_USED_INFO,
     crate::methods::USELESS_ASREF_INFO,
     crate::methods::VEC_RESIZE_TO_ZERO_INFO,

clippy_lints/src/methods/mod.rs

@@ -103,7 +103,6 @@ mod unnecessary_lazy_eval;
 mod unnecessary_literal_unwrap;
 mod unnecessary_sort_by;
 mod unnecessary_to_owned;
-mod unwrap_or_else_default;
 mod unwrap_used;
 mod useless_asref;
 mod utils;
@@ -476,29 +475,40 @@ declare_clippy_lint! {
 
 declare_clippy_lint! {
     /// ### What it does
-    /// Checks for usage of `_.unwrap_or_else(Default::default)` on `Option` and
-    /// `Result` values.
+    /// Checks for usages of the following functions with an argument that constructs a default value
+    /// (e.g., `Default::default` or `String::new`):
+    /// - `unwrap_or`
+    /// - `unwrap_or_else`
+    /// - `or_insert`
+    /// - `or_insert_with`
     ///
     /// ### Why is this bad?
-    /// Readability, these can be written as `_.unwrap_or_default`, which is
-    /// simpler and more concise.
+    /// Readability. Using `unwrap_or_default` in place of `unwrap_or`/`unwrap_or_else`, or `or_default`
+    /// in place of `or_insert`/`or_insert_with`, is simpler and more concise.
+    ///
+    /// ### Known problems
+    /// In some cases, the argument of `unwrap_or`, etc. is needed for type inference. The lint uses a
+    /// heuristic to try to identify such cases. However, the heuristic can produce false negatives.
     ///
     /// ### Examples
     /// ```rust
     /// # let x = Some(1);
-    /// x.unwrap_or_else(Default::default);
-    /// x.unwrap_or_else(u32::default);
+    /// # let mut map = std::collections::HashMap::<u64, String>::new();
+    /// x.unwrap_or(Default::default());
+    /// map.entry(42).or_insert_with(String::new);
     /// ```
     ///
     /// Use instead:
     /// ```rust
     /// # let x = Some(1);
+    /// # let mut map = std::collections::HashMap::<u64, String>::new();
     /// x.unwrap_or_default();
+    /// map.entry(42).or_default();
     /// ```
     #[clippy::version = "1.56.0"]
-    pub UNWRAP_OR_ELSE_DEFAULT,
+    pub UNWRAP_OR_DEFAULT,
     style,
-    "using `.unwrap_or_else(Default::default)`, which is more succinctly expressed as `.unwrap_or_default()`"
+    "using `.unwrap_or`, etc. with an argument that constructs a default value"
 }
 
 declare_clippy_lint! {
@@ -3495,7 +3505,7 @@ impl_lint_pass!(Methods => [
     SHOULD_IMPLEMENT_TRAIT,
     WRONG_SELF_CONVENTION,
     OK_EXPECT,
-    UNWRAP_OR_ELSE_DEFAULT,
+    UNWRAP_OR_DEFAULT,
     MAP_UNWRAP_OR,
     RESULT_MAP_OR_INTO_OPTION,
     OPTION_MAP_OR_NONE,
@@ -3756,8 +3766,7 @@ impl<'tcx> LateLintPass<'tcx> for Methods {
             then {
                 let first_arg_span = first_arg_ty.span;
                 let first_arg_ty = hir_ty_to_ty(cx.tcx, first_arg_ty);
-                let self_ty = TraitRef::identity(cx.tcx, item.owner_id.to_def_id())
-                    .self_ty();
+                let self_ty = TraitRef::identity(cx.tcx, item.owner_id.to_def_id()).self_ty();
                 wrong_self_convention::check(
                     cx,
                     item.ident.name.as_str(),
@@ -3774,8 +3783,7 @@ impl<'tcx> LateLintPass<'tcx> for Methods {
             if item.ident.name == sym::new;
             if let TraitItemKind::Fn(_, _) = item.kind;
             let ret_ty = return_ty(cx, item.owner_id);
-            let self_ty = TraitRef::identity(cx.tcx, item.owner_id.to_def_id())
-                .self_ty();
+            let self_ty = TraitRef::identity(cx.tcx, item.owner_id.to_def_id()).self_ty();
             if !ret_ty.contains(self_ty);
 
             then {
@@ -4134,7 +4142,6 @@ impl Methods {
                         Some(("map", recv, [map_arg], _, _))
                             if map_unwrap_or::check(cx, expr, recv, map_arg, u_arg, &self.msrv) => {},
                         _ => {
-                            unwrap_or_else_default::check(cx, expr, recv, u_arg);
                             unnecessary_lazy_eval::check(cx, expr, recv, u_arg, "unwrap_or");
                         },
                     }

clippy_lints/src/methods/or_fun_call.rs

@@ -1,16 +1,17 @@
 use clippy_utils::diagnostics::span_lint_and_sugg;
 use clippy_utils::eager_or_lazy::switch_to_lazy_eval;
 use clippy_utils::source::snippet_with_context;
-use clippy_utils::ty::{implements_trait, is_type_diagnostic_item};
-use clippy_utils::{contains_return, is_trait_item, last_path_segment};
+use clippy_utils::ty::{expr_type_is_certain, implements_trait, is_type_diagnostic_item};
+use clippy_utils::{contains_return, is_default_equivalent, is_default_equivalent_call, last_path_segment};
 use if_chain::if_chain;
 use rustc_errors::Applicability;
-use rustc_hir as hir;
 use rustc_lint::LateContext;
+use rustc_middle::ty;
 use rustc_span::source_map::Span;
-use rustc_span::symbol::{kw, sym, Symbol};
+use rustc_span::symbol::{self, sym, Symbol};
+use {rustc_ast as ast, rustc_hir as hir};
 
-use super::OR_FUN_CALL;
+use super::{OR_FUN_CALL, UNWRAP_OR_DEFAULT};
 
 /// Checks for the `OR_FUN_CALL` lint.
 #[allow(clippy::too_many_lines)]
@@ -24,53 +25,72 @@ pub(super) fn check<'tcx>(
 ) {
     /// Checks for `unwrap_or(T::new())`, `unwrap_or(T::default())`,
     /// `or_insert(T::new())` or `or_insert(T::default())`.
+    /// Similarly checks for `unwrap_or_else(T::new)`, `unwrap_or_else(T::default)`,
+    /// `or_insert_with(T::new)` or `or_insert_with(T::default)`.
     #[allow(clippy::too_many_arguments)]
     fn check_unwrap_or_default(
         cx: &LateContext<'_>,
         name: &str,
+        receiver: &hir::Expr<'_>,
         fun: &hir::Expr<'_>,
-        arg: &hir::Expr<'_>,
-        or_has_args: bool,
+        call_expr: Option<&hir::Expr<'_>>,
         span: Span,
         method_span: Span,
     ) -> bool {
-        let is_default_default = || is_trait_item(cx, fun, sym::Default);
+        if !expr_type_is_certain(cx, receiver) {
+            return false;
+        }
 
-        let implements_default = |arg, default_trait_id| {
-            let arg_ty = cx.typeck_results().expr_ty(arg);
-            implements_trait(cx, arg_ty, default_trait_id, &[])
+        let is_new = |fun: &hir::Expr<'_>| {
+            if let hir::ExprKind::Path(ref qpath) = fun.kind {
+                let path = last_path_segment(qpath).ident.name;
+                matches!(path, sym::new)
+            } else {
+                false
+            }
         };
 
-        if_chain! {
-            if !or_has_args;
-            if let Some(sugg) = match name {
-                "unwrap_or" => Some("unwrap_or_default"),
-                "or_insert" => Some("or_default"),
-                _ => None,
-            };
-            if let hir::ExprKind::Path(ref qpath) = fun.kind;
-            if let Some(default_trait_id) = cx.tcx.get_diagnostic_item(sym::Default);
-            let path = last_path_segment(qpath).ident.name;
-            // needs to target Default::default in particular or be *::new and have a Default impl
-            // available
-            if (matches!(path, kw::Default) && is_default_default())
-                || (matches!(path, sym::new) && implements_default(arg, default_trait_id));
-
-            then {
-                span_lint_and_sugg(
-                    cx,
-                    OR_FUN_CALL,
-                    method_span.with_hi(span.hi()),
-                    &format!("use of `{name}` followed by a call to `{path}`"),
-                    "try",
-                    format!("{sugg}()"),
-                    Applicability::MachineApplicable,
-                );
-
-                true
+        let output_type_implements_default = |fun| {
+            let fun_ty = cx.typeck_results().expr_ty(fun);
+            if let ty::FnDef(def_id, substs) = fun_ty.kind() {
+                let output_ty = cx.tcx.fn_sig(def_id).subst(cx.tcx, substs).skip_binder().output();
+                cx.tcx
+                    .get_diagnostic_item(sym::Default)
+                    .map_or(false, |default_trait_id| {
+                        implements_trait(cx, output_ty, default_trait_id, substs)
+                    })
             } else {
                 false
             }
+        };
+
+        let sugg = match (name, call_expr.is_some()) {
+            ("unwrap_or", true) | ("unwrap_or_else", false) => "unwrap_or_default",
+            ("or_insert", true) | ("or_insert_with", false) => "or_default",
+            _ => return false,
+        };
+
+        // needs to target Default::default in particular or be *::new and have a Default impl
+        // available
+        if (is_new(fun) && output_type_implements_default(fun))
+            || match call_expr {
+                Some(call_expr) => is_default_equivalent(cx, call_expr),
+                None => is_default_equivalent_call(cx, fun) || closure_body_returns_empty_to_string(cx, fun),
+            }
+        {
+            span_lint_and_sugg(
+                cx,
+                UNWRAP_OR_DEFAULT,
+                method_span.with_hi(span.hi()),
+                &format!("use of `{name}` to construct default value"),
+                "try",
+                format!("{sugg}()"),
+                Applicability::MachineApplicable,
+            );
+
+            true
+        } else {
+            false
         }
     }
 
@@ -168,11 +188,16 @@ pub(super) fn check<'tcx>(
         match inner_arg.kind {
             hir::ExprKind::Call(fun, or_args) => {
                 let or_has_args = !or_args.is_empty();
-                if !check_unwrap_or_default(cx, name, fun, arg, or_has_args, expr.span, method_span) {
+                if or_has_args
+                    || !check_unwrap_or_default(cx, name, receiver, fun, Some(inner_arg), expr.span, method_span)
+                {
                     let fun_span = if or_has_args { None } else { Some(fun.span) };
                     check_general_case(cx, name, method_span, receiver, arg, None, expr.span, fun_span);
                 }
             },
+            hir::ExprKind::Path(..) | hir::ExprKind::Closure(..) => {
+                check_unwrap_or_default(cx, name, receiver, inner_arg, None, expr.span, method_span);
+            },
             hir::ExprKind::Index(..) | hir::ExprKind::MethodCall(..) => {
                 check_general_case(cx, name, method_span, receiver, arg, None, expr.span, None);
             },
@@ -189,3 +214,22 @@ pub(super) fn check<'tcx>(
         }
     }
 }
+
+fn closure_body_returns_empty_to_string(cx: &LateContext<'_>, e: &hir::Expr<'_>) -> bool {
+    if let hir::ExprKind::Closure(&hir::Closure { body, .. }) = e.kind {
+        let body = cx.tcx.hir().body(body);
+
+        if body.params.is_empty()
+            && let hir::Expr{ kind, .. } = &body.value
+            && let hir::ExprKind::MethodCall(hir::PathSegment {ident, ..}, self_arg, _, _) = kind
+            && ident.name == sym::to_string
+            && let hir::Expr{ kind, .. } = self_arg
+            && let hir::ExprKind::Lit(lit) = kind
+            && let ast::LitKind::Str(symbol::kw::Empty, _) = lit.node
+        {
+            return true;
+        }
+    }
+
+    false
+}

clippy_lints/src/methods/unwrap_or_else_default.rs

@@ -30,6 +30,7 @@ pub static RENAMED_LINTS: &[(&str, &str)] = &[
     ("clippy::single_char_push_str", "clippy::single_char_add_str"),
     ("clippy::stutter", "clippy::module_name_repetitions"),
     ("clippy::to_string_in_display", "clippy::recursive_format_impl"),
+    ("clippy::unwrap_or_else_default", "clippy::unwrap_or_default"),
     ("clippy::zero_width_space", "clippy::invisible_characters"),
     ("clippy::cast_ref_to_mut", "cast_ref_to_mut"),
     ("clippy::clone_double_ref", "suspicious_double_ref_op"),