[Pattern Matching] Fix bug causing incorrect diagnostic

dansarginson · Jari Ronkainen · commit 611bd6e2dbf0 · 2024-03-26T18:19:11.000+02:00
Incorrect diagnostic can be emitted when using statement expressions as a pattern substatement in an inspect with a trailing `void` return type. Add a specific check for the void return type. All other cases are handled when we check for convertibility later in semantic analysis. fixes llvm#19
diff --git a/clang/lib/Sema/SemaExpr.cpp b/clang/lib/Sema/SemaExpr.cpp
@@ -16744,8 +16744,17 @@ ExprResult Sema::ActOnStmtExprResult(ExprResult ER) {
   // to perform implicit conversion during the copy initialization.
   if (getCurScope()->isPatternScope()) {
     InspectExpr *IE = getCurFunction()->InspectStack.back().getPointer();
-    if (IE->hasExplicitResultType())
-      T = IE->getType();
+    if (IE->hasExplicitResultType()) {
+      QualType ER = IE->getType();
+
+      // Catch this edge case where we can't make a valid
+      // statement expression result from a void type.
+      // All other cases should be caught elsewhere when
+      // we explore convertibility between the pattern
+      // substatement and the inspect return type.
+      if (!ER.getTypePtr()->isVoidType())
+        T = ER;
+    }
   }
 
   // FIXME: Provide a better location for the initialization.
diff --git a/clang/test/SemaCXX/inspect.cpp b/clang/test/SemaCXX/inspect.cpp
@@ -17,7 +17,7 @@ void a2() {
 
 void b(int x) {
   inspect(x) -> void {
-    __ => 3; // expected-error {{cannot initialize statement expression result of type 'void' with an rvalue of type 'int'}}
+    __ => 3; // expected-error {{resulting expression type 'int' must match trailing result type 'void'}}
   };
 }
 

Original file line number	Diff line number	Diff line change
`@@ -17,7 +17,7 @@ void a2() {`
`17`	`17`
`18`	`18`	`void b(int x) {`
`19`	`19`	`inspect(x) -> void {`
`20`		`- __ => 3; // expected-error {{cannot initialize statement expression result of type 'void' with an rvalue of type 'int'}}`
	`20`	`+ __ => 3; // expected-error {{resulting expression type 'int' must match trailing result type 'void'}}`
`21`	`21`	`};`
`22`	`22`	`}`
`23`	`23`