Prevent Deduplication of LongRunningWarn

compiler/rustc_const_eval/src/const_eval/machine.rs

@@ -641,7 +641,14 @@ fn increment_const_eval_counter(ecx: &mut InterpCx<'tcx, Self>) -> InterpResult<
                 // current number of evaluated terminators is a power of 2. The latter gives us a cheap
                 // way to implement exponential backoff.
                 let span = ecx.cur_span();
-                ecx.tcx.dcx().emit_warn(LongRunningWarn { span, item_span: ecx.tcx.span });
+                // We store a unique number in `force_duplicate` to evade `-Z deduplicate-diagnostics`.
+                // `new_steps` is guaranteed to be unique because `ecx.machine.num_evaluated_steps` is
+                // always increasing.
+                ecx.tcx.dcx().emit_warn(LongRunningWarn {
+                    span,
+                    item_span: ecx.tcx.span,
+                    force_duplicate: new_steps,
+                });
             }
         }
 

compiler/rustc_const_eval/src/errors.rs

@@ -243,6 +243,8 @@ pub struct LongRunningWarn {
     pub span: Span,
     #[help]
     pub item_span: Span,
+    // Used for evading `-Z deduplicate-diagnostics`.
+    pub force_duplicate: usize,
 }
 
 #[derive(Subdiagnostic)]

tests/ui/consts/const-eval/stable-metric/evade-deduplication-issue-118612.stderr

@@ -16,5 +16,77 @@ help: the constant being evaluated
 LL | const FOO: () = {
    | ^^^^^^^^^^^^^
 
-warning: 1 warning emitted
+warning: constant evaluation is taking a long time
+  --> $DIR/evade-deduplication-issue-118612.rs:8:5
+   |
+LL | /     loop {
+LL | |
+LL | |
+LL | |
+...  |
+LL | |         }
+LL | |     }
+   | |_____^ the const evaluator is currently interpreting this expression
+   |
+help: the constant being evaluated
+  --> $DIR/evade-deduplication-issue-118612.rs:6:1
+   |
+LL | const FOO: () = {
+   | ^^^^^^^^^^^^^
+
+warning: constant evaluation is taking a long time
+  --> $DIR/evade-deduplication-issue-118612.rs:8:5
+   |
+LL | /     loop {
+LL | |
+LL | |
+LL | |
+...  |
+LL | |         }
+LL | |     }
+   | |_____^ the const evaluator is currently interpreting this expression
+   |
+help: the constant being evaluated
+  --> $DIR/evade-deduplication-issue-118612.rs:6:1
+   |
+LL | const FOO: () = {
+   | ^^^^^^^^^^^^^
+
+warning: constant evaluation is taking a long time
+  --> $DIR/evade-deduplication-issue-118612.rs:8:5
+   |
+LL | /     loop {
+LL | |
+LL | |
+LL | |
+...  |
+LL | |         }
+LL | |     }
+   | |_____^ the const evaluator is currently interpreting this expression
+   |
+help: the constant being evaluated
+  --> $DIR/evade-deduplication-issue-118612.rs:6:1
+   |
+LL | const FOO: () = {
+   | ^^^^^^^^^^^^^
+
+warning: constant evaluation is taking a long time
+  --> $DIR/evade-deduplication-issue-118612.rs:8:5
+   |
+LL | /     loop {
+LL | |
+LL | |
+LL | |
+...  |
+LL | |         }
+LL | |     }
+   | |_____^ the const evaluator is currently interpreting this expression
+   |
+help: the constant being evaluated
+  --> $DIR/evade-deduplication-issue-118612.rs:6:1
+   |
+LL | const FOO: () = {
+   | ^^^^^^^^^^^^^
+
+warning: 5 warnings emitted