[C++20] [Modules] Pop Expression Evaluation Context when we skip its body during parsing

Close llvm/llvm-project#60275

The root cause of issue 60275 is the imbalance of
PushExpressionEvaluationContext() and PopExpressionEvaluationContext().

See
https://github.com/llvm/llvm-project/blob/f1c4f927f7c15b5efdc3589c050fd0513bf6b303/clang/lib/Parse/Parser.cpp#L1396-L1437

We will PushExpressionEvaluationContext() in ActOnStartOfFunctionDef()
in line 1396 and we should pop it in ActOnFinishFunctionBody later.
However if we skip the function body in line 1402, the expression
evaluation context will not be popped. Then here is the issue report. I
fix the issue by inserting codes to pop the expression evaluation
context explicitly if the function body is skipped. Maybe this looks
like an ad-hoc fix. But if we want to fix this in a pretty way, we
should refactor the current framework for pushing and popping expression
evaluation contexts. Currently there are 23
PushExpressionEvaluationContext() callsities and 21
PopExpressionEvaluationContext() callsites in the code. And it seems not
easy to balance them well and fast. So I suggest to land this fix first.
At least it can prevent the crash.

Reviewed By: cor3ntin

Differential Revision: https://reviews.llvm.org/D143053

Author: ChuanqiXu9

Diff for: clang/lib/Parse/Parser.cpp

@@ -14,6 +14,7 @@
 #include "clang/AST/ASTConsumer.h"
 #include "clang/AST/ASTContext.h"
 #include "clang/AST/DeclTemplate.h"
+#include "clang/AST/ASTLambda.h"
 #include "clang/Basic/FileManager.h"
 #include "clang/Parse/ParseDiagnostic.h"
 #include "clang/Parse/RAIIObjectsForParser.h"
@@ -1404,6 +1405,17 @@ Decl *Parser::ParseFunctionDefinition(ParsingDeclarator &D,
     if (BodyKind == Sema::FnBodyKind::Other)
       SkipFunctionBody();
 
+    // ExpressionEvaluationContext is pushed in ActOnStartOfFunctionDef
+    // and it would be popped in ActOnFinishFunctionBody.
+    // We pop it explcitly here since ActOnFinishFunctionBody won't get called.
+    //
+    // Do not call PopExpressionEvaluationContext() if it is a lambda because
+    // one is already popped when finishing the lambda in BuildLambdaExpr().
+    //
+    // FIXME: It looks not easy to balance PushExpressionEvaluationContext()
+    // and PopExpressionEvaluationContext().
+    if (!isLambdaCallOperator(dyn_cast_if_present<FunctionDecl>(Res)))
+      Actions.PopExpressionEvaluationContext();
     return Res;
   }
 

Diff for: clang/test/Modules/pr60275.cppm

@@ -0,0 +1,40 @@
+// Address: https://github.com/llvm/llvm-project/issues/60275
+//
+// RUN: rm -rf %t
+// RUN: mkdir -p %t
+// RUN: split-file %s %t
+//
+// RUN: %clang_cc1 -std=c++20 -triple %itanium_abi_triple -emit-module-interface %t/a.cppm -o %t/a.pcm
+// RUN: %clang_cc1 -std=c++20 -triple %itanium_abi_triple %t/b.cpp -fmodule-file=%t/a.pcm -emit-llvm -o - | FileCheck %t/b.cpp
+//--- foo.h
+
+consteval void global() {}
+
+//--- a.cppm
+module;
+#include "foo.h"
+export module a;
+
+//--- b.cpp
+#include "foo.h"
+import a;
+
+consteval int b() {
+	return 0;
+}
+
+struct bb {
+	int m = b();
+};
+
+void bbb() {
+	bb x;
+}
+
+// CHECK: define{{.*}}_ZN2bbC2Ev({{.*}}[[THIS:%.+]])
+// CHECK-NEXT: entry:
+// CHECK-NEXT:   [[THIS_ADDR:%.*]] = alloca ptr
+// CHECK-NEXT:   store ptr [[THIS]], ptr [[THIS_ADDR]]
+// CHECK-NEXT:   [[THIS1:%.*]] = load ptr, ptr [[THIS_ADDR]]
+// CHECK-NEXT:   [[M_ADDR:%.*]] = getelementptr{{.*}}%struct.bb, ptr [[THIS1]], i32 0, i32 0
+// CHECK-NEXT:   store i32 0, ptr [[M_ADDR]]