[clangd] Fix hover crash on InitListExpr.

Fixes https://github.com/clangd/clangd/issues/455

Differential Revision: https://reviews.llvm.org/D83546

clang-tools-extra/clangd/Hover.cpp

@@ -329,13 +329,23 @@ void fillFunctionTypeAndParams(HoverInfo &HI, const Decl *D,
 
 llvm::Optional<std::string> printExprValue(const Expr *E,
                                            const ASTContext &Ctx) {
-  Expr::EvalResult Constant;
+  // InitListExpr has two forms, syntactic and semantic. They are the same thing
+  // (refer to a same AST node) in most cases.
+  // When they are different, RAV returns the syntactic form, and we should feed
+  // the semantic form to EvaluateAsRValue.
+  if (const auto *ILE = llvm::dyn_cast<InitListExpr>(E)) {
+    if (!ILE->isSemanticForm())
+      E = ILE->getSemanticForm();
+  }
+
   // Evaluating [[foo]]() as "&foo" isn't useful, and prevents us walking up
   // to the enclosing call.
   QualType T = E->getType();
   if (T.isNull() || T->isFunctionType() || T->isFunctionPointerType() ||
       T->isFunctionReferenceType())
     return llvm::None;
+
+  Expr::EvalResult Constant;
   // Attempt to evaluate. If expr is dependent, evaluation crashes!
   if (E->isValueDependent() || !E->EvaluateAsRValue(Constant, Ctx) ||
       // Disable printing for record-types, as they are usually confusing and

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

@@ -801,6 +801,21 @@ class Foo {})cpp";
          HI.LocalScope = "Foo::";
          HI.Type = "int";
          HI.AccessSpecifier = "public";
+       }},
+       {// No crash on InitListExpr.
+        R"cpp(
+          struct Foo {
+            int a[10];
+          };
+          constexpr Foo k2 = {
+            ^[[{]]1} // FIXME: why the hover range is 1 character?
+          };
+         )cpp",
+       [](HoverInfo &HI) {
+         HI.Name = "expression";
+         HI.Kind = index::SymbolKind::Unknown;
+         HI.Type = "int [10]";
+         HI.Value = "{1}";
        }}};
   for (const auto &Case : Cases) {
     SCOPED_TRACE(Case.Code);