Auto merge of rust-lang#88175 - camsteffen:let-desugar-span, r=Manishearth

Add expansion to while desugar spans

In the same vein as rust-lang#88163, this reverts a change in Clippy behavior as a result of rust-lang#80357 (and reverts some `#[allow]`s): This changes `clippy::blocks_in_if_conditions` to not fire on `while` loops. Though we might actually want Clippy to lint those cases, we should introduce the change purposefully, with tests, and possibly under a different lint name.

The actual change here is to add a desugaring expansion to the spans when lowering a `while` loop.

r? `@Manishearth`

Author: bors

Diff for: compiler/rustc_ast_lowering/src/expr.rs

@@ -100,10 +100,13 @@ impl<'hir> LoweringContext<'_, 'hir> {
                 ExprKind::If(ref cond, ref then, ref else_opt) => {
                     self.lower_expr_if(cond, then, else_opt.as_deref())
                 }
-                ExprKind::While(ref cond, ref body, opt_label) => self
-                    .with_loop_scope(e.id, |this| {
-                        this.lower_expr_while_in_loop_scope(e.span, cond, body, opt_label)
-                    }),
+                ExprKind::While(ref cond, ref body, opt_label) => {
+                    self.with_loop_scope(e.id, |this| {
+                        let span =
+                            this.mark_span_with_reason(DesugaringKind::WhileLoop, e.span, None);
+                        this.lower_expr_while_in_loop_scope(span, cond, body, opt_label)
+                    })
+                }
                 ExprKind::Loop(ref body, opt_label) => self.with_loop_scope(e.id, |this| {
                     hir::ExprKind::Loop(
                         this.lower_block(body, false),

Diff for: compiler/rustc_middle/src/lint.rs

@@ -389,9 +389,9 @@ pub fn struct_lint_level<'s, 'd>(
 pub fn in_external_macro(sess: &Session, span: Span) -> bool {
     let expn_data = span.ctxt().outer_expn_data();
     match expn_data.kind {
-        ExpnKind::Inlined | ExpnKind::Root | ExpnKind::Desugaring(DesugaringKind::ForLoop(_)) => {
-            false
-        }
+        ExpnKind::Inlined
+        | ExpnKind::Root
+        | ExpnKind::Desugaring(DesugaringKind::ForLoop(_) | DesugaringKind::WhileLoop) => false,
         ExpnKind::AstPass(_) | ExpnKind::Desugaring(_) => true, // well, it's "external"
         ExpnKind::Macro(MacroKind::Bang, _) => {
             // Dummy span for the `def_site` means it's an external macro.

Diff for: compiler/rustc_span/src/hygiene.rs

@@ -1101,6 +1101,7 @@ pub enum DesugaringKind {
     Await,
     ForLoop(ForLoopLoc),
     LetElse,
+    WhileLoop,
 }
 
 /// A location in the desugaring of a `for` loop
@@ -1122,6 +1123,7 @@ impl DesugaringKind {
             DesugaringKind::OpaqueTy => "`impl Trait`",
             DesugaringKind::ForLoop(_) => "`for` loop",
             DesugaringKind::LetElse => "`let...else`",
+            DesugaringKind::WhileLoop => "`while` loop",
         }
     }
 }

Diff for: compiler/rustc_typeck/src/check/coercion.rs

@@ -54,7 +54,7 @@ use rustc_middle::ty::subst::SubstsRef;
 use rustc_middle::ty::{self, ToPredicate, Ty, TypeAndMut};
 use rustc_session::parse::feature_err;
 use rustc_span::symbol::sym;
-use rustc_span::{self, BytePos, Span};
+use rustc_span::{self, BytePos, DesugaringKind, Span};
 use rustc_target::spec::abi::Abi;
 use rustc_trait_selection::traits::error_reporting::InferCtxtExt;
 use rustc_trait_selection::traits::{self, ObligationCause, ObligationCauseCode};
@@ -1536,8 +1536,10 @@ impl<'tcx, 'exprs, E: AsCoercionSite> CoerceMany<'tcx, 'exprs, E> {
                 // If the block is from an external macro or try (`?`) desugaring, then
                 // do not suggest adding a semicolon, because there's nowhere to put it.
                 // See issues #81943 and #87051.
-                if cond_expr.span.desugaring_kind().is_none()
-                    && !in_external_macro(fcx.tcx.sess, cond_expr.span)
+                if matches!(
+                    cond_expr.span.desugaring_kind(),
+                    None | Some(DesugaringKind::WhileLoop)
+                ) && !in_external_macro(fcx.tcx.sess, cond_expr.span)
                     && !matches!(
                         cond_expr.kind,
                         hir::ExprKind::Match(.., hir::MatchSource::TryDesugar)

Diff for: src/tools/clippy/tests/ui/crashes/issues_loop_mut_cond.rs

@@ -1,4 +1,3 @@
-#![allow(clippy::blocks_in_if_conditions)]
 #![allow(dead_code)]
 
 /// Issue: https://github.com/rust-lang/rust-clippy/issues/2596

Diff for: src/tools/clippy/tests/ui/infinite_loop.rs

@@ -1,5 +1,3 @@
-#![allow(clippy::blocks_in_if_conditions)]
-
 fn fn_val(i: i32) -> i32 {
     unimplemented!()
 }

Diff for: src/tools/clippy/tests/ui/infinite_loop.stderr

@@ -1,5 +1,5 @@
 error: variables in the condition are not mutated in the loop body
-  --> $DIR/infinite_loop.rs:22:11
+  --> $DIR/infinite_loop.rs:20:11
    |
 LL |     while y < 10 {
    |           ^^^^^^
@@ -8,71 +8,71 @@ LL |     while y < 10 {
    = note: this may lead to an infinite or to a never running loop
 
 error: variables in the condition are not mutated in the loop body
-  --> $DIR/infinite_loop.rs:27:11
+  --> $DIR/infinite_loop.rs:25:11
    |
 LL |     while y < 10 && x < 3 {
    |           ^^^^^^^^^^^^^^^
    |
    = note: this may lead to an infinite or to a never running loop
 
 error: variables in the condition are not mutated in the loop body
-  --> $DIR/infinite_loop.rs:34:11
+  --> $DIR/infinite_loop.rs:32:11
    |
 LL |     while !cond {
    |           ^^^^^
    |
    = note: this may lead to an infinite or to a never running loop
 
 error: variables in the condition are not mutated in the loop body
-  --> $DIR/infinite_loop.rs:78:11
+  --> $DIR/infinite_loop.rs:76:11
    |
 LL |     while i < 3 {
    |           ^^^^^
    |
    = note: this may lead to an infinite or to a never running loop
 
 error: variables in the condition are not mutated in the loop body
-  --> $DIR/infinite_loop.rs:83:11
+  --> $DIR/infinite_loop.rs:81:11
    |
 LL |     while i < 3 && j > 0 {
    |           ^^^^^^^^^^^^^^
    |
    = note: this may lead to an infinite or to a never running loop
 
 error: variables in the condition are not mutated in the loop body
-  --> $DIR/infinite_loop.rs:87:11
+  --> $DIR/infinite_loop.rs:85:11
    |
 LL |     while i < 3 {
    |           ^^^^^
    |
    = note: this may lead to an infinite or to a never running loop
 
 error: variables in the condition are not mutated in the loop body
-  --> $DIR/infinite_loop.rs:102:11
+  --> $DIR/infinite_loop.rs:100:11
    |
 LL |     while i < 3 {
    |           ^^^^^
    |
    = note: this may lead to an infinite or to a never running loop
 
 error: variables in the condition are not mutated in the loop body
-  --> $DIR/infinite_loop.rs:107:11
+  --> $DIR/infinite_loop.rs:105:11
    |
 LL |     while i < 3 {
    |           ^^^^^
    |
    = note: this may lead to an infinite or to a never running loop
 
 error: variables in the condition are not mutated in the loop body
-  --> $DIR/infinite_loop.rs:173:15
+  --> $DIR/infinite_loop.rs:171:15
    |
 LL |         while self.count < n {
    |               ^^^^^^^^^^^^^^
    |
    = note: this may lead to an infinite or to a never running loop
 
 error: variables in the condition are not mutated in the loop body
-  --> $DIR/infinite_loop.rs:181:11
+  --> $DIR/infinite_loop.rs:179:11
    |
 LL |     while y < 10 {
    |           ^^^^^^
@@ -82,7 +82,7 @@ LL |     while y < 10 {
    = help: rewrite it as `if cond { loop { } }`
 
 error: variables in the condition are not mutated in the loop body
-  --> $DIR/infinite_loop.rs:188:11
+  --> $DIR/infinite_loop.rs:186:11
    |
 LL |     while y < 10 {
    |           ^^^^^^