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

Add expansion to while desugar spans

In the same vein as #88163, this reverts a change in Clippy behavior as a result of #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`

4 files changed, 17 insertions, 10 deletions

diff --git a/compiler/rustc_ast_lowering/src/expr.rs b/compiler/rustc_ast_lowering/src/expr.rs
index a6ea4aa8923..6027027428e 100644
--- a/compiler/rustc_ast_lowering/src/expr.rs
+++ b/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 --git a/compiler/rustc_middle/src/lint.rs b/compiler/rustc_middle/src/lint.rs
index 60cb78d902e..37fec0ac38c 100644
--- a/compiler/rustc_middle/src/lint.rs
+++ b/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 --git a/compiler/rustc_span/src/hygiene.rs b/compiler/rustc_span/src/hygiene.rs
index 29af6b38bf4..aa15febe885 100644
--- a/compiler/rustc_span/src/hygiene.rs
+++ b/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 --git a/compiler/rustc_typeck/src/check/coercion.rs b/compiler/rustc_typeck/src/check/coercion.rs
index 79763942d05..e34b8d998b1 100644
--- a/compiler/rustc_typeck/src/check/coercion.rs
+++ b/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)