[flang-commits] [flang] [Flang][Semantics] Fix crash on invalid function result declaration (PR #194648)

[via flang-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-flang-semantics

Author: ShashwathiNavada

<details>
<summary>Changes</summary>

Fixes https://github.com/llvm/llvm-project/issues/194596.

When the function result symbol is encountered while the compiler is already completing the function result type, flang could recursively re-enter _CompleteFunctionResultType()_ and crash on invalid code.
Example:
```
character*(a) function bb() result(a) ! ERROR
implicit integer(a)
A = "a"
end
```
Instead of crashing on conflicting declarations, flang now reports an “already declared” error and stops further recursion.

---
Full diff: https://github.com/llvm/llvm-project/pull/194648.diff


1 Files Affected:

- (modified) flang/lib/Semantics/resolve-names.cpp (+11-1) 


``````````diff
diff --git a/flang/lib/Semantics/resolve-names.cpp b/flang/lib/Semantics/resolve-names.cpp
index b6907cc792d76..409a793534399 100644
--- a/flang/lib/Semantics/resolve-names.cpp
+++ b/flang/lib/Semantics/resolve-names.cpp
@@ -496,6 +496,7 @@ class FuncResultStack {
     // Result symbol
     Symbol *resultSymbol{nullptr};
     bool inFunctionStmt{false}; // true between Pre/Post of FunctionStmt
+    bool completingType{false}; // re-entrancy guard for CompleteFunctionResultType
     // Functions with previous implicitly-typed references get those types
     // checked against their later definitions.
     const DeclTypeSpec *previousImplicitType{nullptr};
@@ -2874,6 +2875,7 @@ void FuncResultStack::CompleteFunctionResultType() {
   if (info && &info->scope == &scopeHandler_.currScope() &&
       info->resultSymbol) {
     if (info->parsedType) {
+      auto completingTypeScope{common::ScopedSet(info->completingType, true)};
       scopeHandler_.messageHandler().set_currStmtSource(info->source);
       if (const auto *type{
               scopeHandler_.ProcessTypeSpec(*info->parsedType, true)}) {
@@ -2908,7 +2910,15 @@ void FuncResultStack::CompleteFunctionResultType() {
 void FuncResultStack::CompleteTypeIfFunctionResult(Symbol &symbol) {
   if (FuncInfo * info{Top()}) {
     if (info->resultSymbol == &symbol) {
-      CompleteFunctionResultType();
+      if (info->completingType) {
+        if (!scopeHandler_.context().HasError(symbol)) {
+          scopeHandler_.SayAlreadyDeclared(symbol.name(),
+              info->resultName ? info->resultName->source : symbol.name());
+          scopeHandler_.context().SetError(symbol);
+        }
+      } else {
+        CompleteFunctionResultType();
+      }
     }
   }
 }

``````````

</details>


https://github.com/llvm/llvm-project/pull/194648