[clangd] Fix an inlay-hint crash on a broken designator.

[kadircet]

clang-tools-extra/clangd/InlayHints.cpp

140

we should have this bail out after introducing the scope_exit below to make sure we skip the field.

clang-tools-extra/clangd/unittests/InlayHintTests.cpp

1427

a better test would be

struct A{};
struct Foo {int a; int b;};
Foo f{A(), 1);

and make sure we still get the hints for 1 as b.

[hokein]

address review comment -- make sure we skip the corresponding field when its
init expr is null, and polish the testcase.

clang-tools-extra/clangd/InlayHints.cpp

140

good catch! You're right.

[kadircet]

clang-tools-extra/clangd/InlayHints.cpp

143–144

nit: can you also update the comment to mention broken initializer (and maybe even a fixme to handle these, as in theory this is likely spelled in the code, but wasn't retained in the AST even as a recoveryexpr, hence we still have a place to attach the hint)

[hokein]

update the comment.

clang-tools-extra/clangd/InlayHints.cpp

143–144

Done, updated the comment. I'd rather leave out the FIXME (it is unclear that we will address it).

The InitListExpr is tricky, the AST nodes is preserved in the syntactic form for InitListExpr (go-to-definition actually works on the broken initializer A() ), but here we're using the *semantic*-form...

clang-tools-extra/clangd/InlayHints.cpp

void collectDesignators(const InitListExpr *Sem,
   assert(Sem->isSemanticForm());
 
   // The elements of the semantic form all correspond to direct subobjects of
   // the aggregate type. `Fields` iterates over these subobject names.
   AggregateDesignatorNames Fields(Sem->getType());
   if (!Fields)
     return;
   for (const Expr *Init : Sem->inits()) {
     auto Next = llvm::make_scope_exit([&, Size(Prefix.size())] {
       Fields.next();       // Always advance to the next subobject name.
       Prefix.resize(Size); // Erase any designator we appended.
     });
-    if (llvm::isa<ImplicitValueInitExpr>(Init))
-      continue; // a "hole" for a subobject that was not explicitly initialized
+    // Skip for a broken initializer or if it is a "hole" in a subobject that
+    // was not explicitly initialized.
+    if (!Init || llvm::isa<ImplicitValueInitExpr>(Init))
+      continue;
 
     const auto *BraceElidedSubobject = llvm::dyn_cast<InitListExpr>(Init);
     if (BraceElidedSubobject &&
         NestedBraces.contains(BraceElidedSubobject->getLBraceLoc()))
       BraceElidedSubobject = nullptr; // there were braces!
 
     if (!Fields.append(Prefix, BraceElidedSubobject != nullptr))
       continue; // no designator available for this subobject

clang-tools-extra/clangd/unittests/InlayHintTests.cpp

assertDesignatorHints(R"cpp(
     struct Copyable { int x; } c;
     Copyable d{c};
 
     struct Constructible { Constructible(int x); };
     Constructible x{42};
   )cpp" /*no designator hints expected (but param hints!)*/);
 }
 
+TEST(DesignatorHints, NoCrash) {
+  assertDesignatorHints(R"cpp(
+    /*error-ok*/
+    struct A {};
+    struct Foo {int a; int b;};
+    void test() {
+      Foo f{A(), $b[[1]]};
+    }
+  )cpp", ExpectedHint{".b=", "b"});
+}
+
 TEST(InlayHints, RestrictRange) {
   Annotations Code(R"cpp(
     auto a = false;
     [[auto b = 1;
     auto c = '2';]]
     auto d = 3.f;
   )cpp");
   auto AST = TestTU::withCode(Code.code()).build();