[clang] [Clang] Fix null pointer dereference in enum debug info generation (PR #97105)

[Tom Honermann via cfe-commits]

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@@ -98,3 +98,6 @@ enum E8 { A8 = -128, B8 = 127 } x8;
 // CHECK-NOT: DIFlagEnumClass
 // CHECK: !DIEnumerator(name: "A8", value: -128)
 
+// Forward declaration of an enum class.
+enum class Color : int;
+// CHECK-NOT: !DICompositeType(tag: DW_TAG_enumeration_type, name: "Color"
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tahonermann wrote:

I spent some time experimenting and debugging today but have not been able to find a way for `CGDebugInfo::CreateTypeDefinition(const EnumType *)` to be invoked without an available definition. I tried various uses of non-standard enumeration forward declarations, but non-suppressible errors were issued for every case I tried that I thought might lead to generation of a debug info type.

The most interesting scenario I played with involved use of the enumeration type within its own definition. In that context, the type is incomplete, but a definition is (being made) available. I wouldn't expect generation of debug info to ever be sensitive to such a context though. I know little about how debug information is generated, but seeing as the function under discussion is part of code generation, I wouldn't expect a not-yet-completed definition to ever be observed.

I think adding an assert as proposed in https://github.com/llvm/llvm-project/pull/105556 suffices to address the static analysis concern.

https://github.com/llvm/llvm-project/pull/97105