Rollup merge of #67709 - petrochenkov:nodedup2, r=Centril

Introduce an option for disabling deduplication of diagnostics

With the intent of using it in UI tests (https://github.com/rust-lang/rust/pull/67122).

The option is boolean (`-Z deduplicate-diagnostics=yes/no`) and can be specified multiple times with later values overriding earlier values (`-Z deduplicate-diagnostics=no -Z deduplicate-diagnostics=yes` == `-Z deduplicate-diagnostics=yes`), so it can be set in a hierarchical way, e.g. UI testing infra may disable the deduplication by default with specific tests being able to enable it back.

1 files changed, 8 insertions, 5 deletions

diff --git a/src/librustc_errors/lib.rs b/src/librustc_errors/lib.rs
index aa2865a75f9..2279ed85954 100644
--- a/src/librustc_errors/lib.rs
+++ b/src/librustc_errors/lib.rs
@@ -329,6 +329,8 @@ pub struct HandlerFlags {
     /// show macro backtraces even for non-local macros.
     /// (rustc: see `-Z external-macro-backtrace`)
     pub external_macro_backtrace: bool,
+    /// If true, identical diagnostics are reported only once.
+    pub deduplicate_diagnostics: bool,
 }
 
 impl Drop for HandlerInner {
@@ -736,16 +738,17 @@ impl HandlerInner {
             self.emitted_diagnostic_codes.insert(code.clone());
         }
 
-        let diagnostic_hash = {
+        let already_emitted = |this: &mut Self| {
             use std::hash::Hash;
             let mut hasher = StableHasher::new();
             diagnostic.hash(&mut hasher);
-            hasher.finish()
+            let diagnostic_hash = hasher.finish();
+            !this.emitted_diagnostics.insert(diagnostic_hash)
         };
 
-        // Only emit the diagnostic if we haven't already emitted an equivalent
-        // one:
-        if self.emitted_diagnostics.insert(diagnostic_hash) {
+        // Only emit the diagnostic if we've been asked to deduplicate and
+        // haven't already emitted an equivalent diagnostic.
+        if !(self.flags.deduplicate_diagnostics && already_emitted(self)) {
             self.emitter.emit_diagnostic(diagnostic);
             if diagnostic.is_error() {
                 self.deduplicated_err_count += 1;