Auto merge of #114774 - Enselic:less-move-size-noise, r=oli-obk

Avoid duplicate `large_assignments` lints

By checking for overlapping spans.

This PR does the "reduce noisiness" task in #83518.

r? `@oli-obk` who added E-mentor and E-help-wanted and wrote the initial code.

(The fix itself is in dc82736. The two commits before that are just small refactorings.)

compiler/rustc_monomorphize/src/collector.rs

@@ -590,6 +590,8 @@ struct MirUsedCollector<'a, 'tcx> {
     body: &'a mir::Body<'tcx>,
     output: &'a mut MonoItems<'tcx>,
     instance: Instance<'tcx>,
+    /// Spans for move size lints already emitted. Helps avoid duplicate lints.
+    move_size_spans: Vec<Span>,
 }
 
 impl<'a, 'tcx> MirUsedCollector<'a, 'tcx> {
@@ -604,6 +606,45 @@ impl<'a, 'tcx> MirUsedCollector<'a, 'tcx> {
             ty::EarlyBinder::bind(value),
         )
     }
+
+    fn check_move_size(&mut self, limit: usize, operand: &mir::Operand<'tcx>, location: Location) {
+        let limit = Size::from_bytes(limit);
+        let ty = operand.ty(self.body, self.tcx);
+        let ty = self.monomorphize(ty);
+        let Ok(layout) = self.tcx.layout_of(ty::ParamEnv::reveal_all().and(ty)) else { return };
+        if layout.size <= limit {
+            return;
+        }
+        debug!(?layout);
+        let source_info = self.body.source_info(location);
+        debug!(?source_info);
+        for span in &self.move_size_spans {
+            if span.overlaps(source_info.span) {
+                return;
+            }
+        }
+        let lint_root = source_info.scope.lint_root(&self.body.source_scopes);
+        debug!(?lint_root);
+        let Some(lint_root) = lint_root else {
+            // This happens when the issue is in a function from a foreign crate that
+            // we monomorphized in the current crate. We can't get a `HirId` for things
+            // in other crates.
+            // FIXME: Find out where to report the lint on. Maybe simply crate-level lint root
+            // but correct span? This would make the lint at least accept crate-level lint attributes.
+            return;
+        };
+        self.tcx.emit_spanned_lint(
+            LARGE_ASSIGNMENTS,
+            lint_root,
+            source_info.span,
+            LargeAssignmentsLint {
+                span: source_info.span,
+                size: layout.size.bytes(),
+                limit: limit.bytes(),
+            },
+        );
+        self.move_size_spans.push(source_info.span);
+    }
 }
 
 impl<'a, 'tcx> MirVisitor<'tcx> for MirUsedCollector<'a, 'tcx> {
@@ -803,40 +844,9 @@ impl<'a, 'tcx> MirVisitor<'tcx> for MirUsedCollector<'a, 'tcx> {
 
     fn visit_operand(&mut self, operand: &mir::Operand<'tcx>, location: Location) {
         self.super_operand(operand, location);
-        let limit = self.tcx.move_size_limit().0;
-        if limit == 0 {
-            return;
-        }
-        let limit = Size::from_bytes(limit);
-        let ty = operand.ty(self.body, self.tcx);
-        let ty = self.monomorphize(ty);
-        let layout = self.tcx.layout_of(ty::ParamEnv::reveal_all().and(ty));
-        if let Ok(layout) = layout {
-            if layout.size > limit {
-                debug!(?layout);
-                let source_info = self.body.source_info(location);
-                debug!(?source_info);
-                let lint_root = source_info.scope.lint_root(&self.body.source_scopes);
-                debug!(?lint_root);
-                let Some(lint_root) = lint_root else {
-                    // This happens when the issue is in a function from a foreign crate that
-                    // we monomorphized in the current crate. We can't get a `HirId` for things
-                    // in other crates.
-                    // FIXME: Find out where to report the lint on. Maybe simply crate-level lint root
-                    // but correct span? This would make the lint at least accept crate-level lint attributes.
-                    return;
-                };
-                self.tcx.emit_spanned_lint(
-                    LARGE_ASSIGNMENTS,
-                    lint_root,
-                    source_info.span,
-                    LargeAssignmentsLint {
-                        span: source_info.span,
-                        size: layout.size.bytes(),
-                        limit: limit.bytes(),
-                    },
-                )
-            }
+        let move_size_limit = self.tcx.move_size_limit().0;
+        if move_size_limit > 0 {
+            self.check_move_size(move_size_limit, operand, location);
         }
     }
 
@@ -1363,7 +1373,8 @@ fn collect_used_items<'tcx>(
     output: &mut MonoItems<'tcx>,
 ) {
     let body = tcx.instance_mir(instance.def);
-    MirUsedCollector { tcx, body: &body, output, instance }.visit_body(&body);
+    MirUsedCollector { tcx, body: &body, output, instance, move_size_spans: vec![] }
+        .visit_body(&body);
 }
 
 #[instrument(skip(tcx, output), level = "debug")]

tests/ui/async-await/large_moves.attribute.stderr

@@ -12,20 +12,12 @@ LL | #![deny(large_assignments)]
    |         ^^^^^^^^^^^^^^^^^
 
 error: moving 10024 bytes
-  --> $DIR/large_moves.rs:19:13
-   |
-LL |     let z = (x, 42);
-   |             ^^^^^^^ value moved from here
-   |
-   = note: The current maximum size is 1000, but it can be customized with the move_size_limit attribute: `#![move_size_limit = "..."]`
-
-error: moving 10024 bytes
-  --> $DIR/large_moves.rs:21:13
+  --> $DIR/large_moves.rs:20:13
    |
 LL |     let a = z.0;
    |             ^^^ value moved from here
    |
    = note: The current maximum size is 1000, but it can be customized with the move_size_limit attribute: `#![move_size_limit = "..."]`
 
-error: aborting due to 3 previous errors
+error: aborting due to 2 previous errors
 

tests/ui/async-await/large_moves.option.stderr

@@ -12,20 +12,12 @@ LL | #![deny(large_assignments)]
    |         ^^^^^^^^^^^^^^^^^
 
 error: moving 10024 bytes
-  --> $DIR/large_moves.rs:19:13
-   |
-LL |     let z = (x, 42);
-   |             ^^^^^^^ value moved from here
-   |
-   = note: The current maximum size is 1000, but it can be customized with the move_size_limit attribute: `#![move_size_limit = "..."]`
-
-error: moving 10024 bytes
-  --> $DIR/large_moves.rs:21:13
+  --> $DIR/large_moves.rs:20:13
    |
 LL |     let a = z.0;
    |             ^^^ value moved from here
    |
    = note: The current maximum size is 1000, but it can be customized with the move_size_limit attribute: `#![move_size_limit = "..."]`
 
-error: aborting due to 3 previous errors
+error: aborting due to 2 previous errors
 

tests/ui/async-await/large_moves.rs

@@ -17,7 +17,6 @@ fn main() {
         dbg!(y);
     };
     let z = (x, 42); //~ ERROR large_assignments
-    //~^ ERROR large_assignments
     let a = z.0; //~ ERROR large_assignments
     let b = z.1;
 }