[clang] [Clang] Fix handling of brace ellison when building deduction guides (PR #94889)

[Younan Zhang via cfe-commits]

================
@@ -10918,22 +10944,24 @@ QualType Sema::DeduceTemplateSpecializationFromInitializer(
       if (!(RD->getDefinition() && RD->isAggregate()))
         return;
       QualType Ty = Context.getRecordType(RD);
-      SmallVector<QualType, 8> ElementTypes;
-
-      InitListChecker CheckInitList(*this, Entity, ListInit, Ty, ElementTypes);
-      if (!CheckInitList.HadError()) {
+      auto BuildAggregateDeductionGuide = [&](MutableArrayRef<QualType>
+                                                  ElementTypes,
+                                              bool BracedVersion = false) {
+        if (ElementTypes.empty())
+          return;
         // C++ [over.match.class.deduct]p1.8:
         //   if e_i is of array type and x_i is a braced-init-list, T_i is an
         //   rvalue reference to the declared type of e_i and
         // C++ [over.match.class.deduct]p1.9:
-        //   if e_i is of array type and x_i is a bstring-literal, T_i is an
+        //   if e_i is of array type and x_i is a string-literal, T_i is an
         //   lvalue reference to the const-qualified declared type of e_i and
         // C++ [over.match.class.deduct]p1.10:
         //   otherwise, T_i is the declared type of e_i
-        for (int I = 0, E = ListInit->getNumInits();
+        for (int I = 0, E = BracedVersion ? ElementTypes.size()
+                                          : ListInit->getNumInits();
              I < E && !isa<PackExpansionType>(ElementTypes[I]); ++I)
           if (ElementTypes[I]->isArrayType()) {
-            if (isa<InitListExpr>(ListInit->getInit(I)))
+            if (isa<InitListExpr, DesignatedInitExpr>(ListInit->getInit(I)))
----------------
zyn0217 wrote:

I hope I'm reading it correctly. If we look at [`dcl.init.general`](https://eel.is/c++draft/dcl.init.general#nt:braced-init-list), a `braced-init-list` is defined as
```
{ initializer-list, ...}
{ designated-initializer-list, ...}
{ }
```

https://github.com/llvm/llvm-project/pull/94889