[PATCH] D147626: [clang] Do not crash when initializing union with flexible array member

[Shafik Yaghmour via Phabricator via cfe-commits]

shafik added a subscriber: rsmith.
shafik added a comment.

Thank you for this fix.



================
Comment at: clang/lib/Sema/SemaInit.cpp:808
       unsigned NumElems = numStructUnionElements(ILE->getType());
-      if (RDecl->hasFlexibleArrayMember())
+      if (!RDecl->isUnion() && RDecl->hasFlexibleArrayMember())
         ++NumElems;
----------------
Fznamznon wrote:
> Just for some context, numStructUnionElements checks that there is a flexible array member and returns number_of_initializable_fields-1 for structs. For unions it just returns 1 or 0, so flexible array member caused adding one more element to initlistexpr that was never properly handled.
> 
> Instead of doing this change, we could probably never enter initialization since the record (union) declaration is not valid, but that is not the case even for other types of errors in code, for example, I've tried declaring field of struct with a typo:
> 
> ```
> struct { cha x[]; } r = {1}; 
> ```
> Initialization is still performed by clang.
> Also, it seems MSVC considers flexible array member inside union as valid, so the test code is probably not always invalid.
I am not sure what to think here, looking at gcc documentation for this extension: https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html 

and using the following code:

```
struct f1 {
  int x; int y[];
} f1 = { 1, { 2, 3, 4 } }; // #1

struct f2 {
  struct f1 f1; int data[3];
} f2 = { { 1 }, { 2, 3, 4 } }; // #2

struct { char x[]; } r = {1};  // #3
```

gcc rejects 2 and 3 even though 2 comes from their documentation. Clang warns on 2 and MSVC rejects 2

CC @aaron.ballman @rsmith 


Repository:
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https://reviews.llvm.org/D147626