Fix overflow in rustc happening if the err_count() is reduced in a stage.

hkratz · hkratz · commit 5ff06fb77f90 · 2021-08-04T14:25:45.000Z
This can happen if stashed diagnostics are removed or replaced with fewer errors. The semantics stay the same if built without overflow. Fixes rust-lang#84219.
diff --git a/compiler/rustc_session/src/session.rs b/compiler/rustc_session/src/session.rs
@@ -450,8 +450,7 @@ impl Session {
     {
         let old_count = self.err_count();
         let result = f();
-        let errors = self.err_count() - old_count;
-        if errors == 0 { Ok(result) } else { Err(ErrorReported) }
+        if self.err_count() == old_count { Ok(result) } else { Err(ErrorReported) }
     }
     pub fn span_warn<S: Into<MultiSpan>>(&self, sp: S, msg: &str) {
         self.diagnostic().span_warn(sp, msg)

Original file line number	Diff line number	Diff line change
`@@ -450,8 +450,7 @@ impl Session {`
`450`	`450`	`{`
`451`	`451`	`let old_count = self.err_count();`
`452`	`452`	`let result = f();`
`453`		`- let errors = self.err_count() - old_count;`
`454`		`- if errors == 0 { Ok(result) } else { Err(ErrorReported) }`
	`453`	`+ if self.err_count() == old_count { Ok(result) } else { Err(ErrorReported) }`
`455`	`454`	`}`
`456`	`455`	`pub fn span_warn<S: Into<MultiSpan>>(&self, sp: S, msg: &str) {`
`457`	`456`	`self.diagnostic().span_warn(sp, msg)`