[clang] Enable code completion of designated initializers in Compound Literal Expressions

[kadircet]

Summary

PreferedType were not set when parsing compound literals, hence
designated initializers were not available as code completion suggestions.

This patch sets the preferedtype to parsed type for the following initializer
list.

Fixes https://github.com/clangd/clangd/issues/142.

clang/lib/Parse/ParseExpr.cpp

 /// \endverbatim
 ExprResult
 Parser::ParseCompoundLiteralExpression(ParsedType Ty,
                                        SourceLocation LParenLoc,
                                        SourceLocation RParenLoc) {
   assert(Tok.is(tok::l_brace) && "Not a compound literal!");
   if (!getLangOpts().C99)   // Compound literals don't exist in C90.
     Diag(LParenLoc, diag::ext_c99_compound_literal);
+  PreferredType.enterTypeCast(Tok.getLocation(), Ty.get());
   ExprResult Result = ParseInitializer();
   if (!Result.isInvalid() && Ty)
     return Actions.ActOnCompoundLiteral(LParenLoc, Ty, RParenLoc, Result.get());
   return Result;
 }
 
 /// ParseStringLiteralExpression - This handles the various token types that
 /// form string literals, and also handles string concatenation [C99 5.1.1.2,

clang/test/CodeCompletion/desig-init.cpp

void foo() {
 
   // FIXME: Handle nested designators
   // RUN: %clang_cc1 -fsyntax-only -code-completion-patterns -code-completion-at=%s:11:20 %s -o - | count 0
 
   Base B = {.t = 2};
   auto z = [](Base B) {};
   z({.t = 1});
   z(Base{.t = 2});
+  z((Base){.t = 2});
   // RUN: %clang_cc1 -fsyntax-only -code-completion-patterns -code-completion-at=%s:22:14 %s -o - -std=c++2a | FileCheck -check-prefix=CHECK-CC2 %s
   // RUN: %clang_cc1 -fsyntax-only -code-completion-patterns -code-completion-at=%s:24:7 %s -o - -std=c++2a | FileCheck -check-prefix=CHECK-CC2 %s
   // RUN: %clang_cc1 -fsyntax-only -code-completion-patterns -code-completion-at=%s:25:11 %s -o - -std=c++2a | FileCheck -check-prefix=CHECK-CC2 %s
+  // RUN: %clang_cc1 -fsyntax-only -code-completion-patterns -code-completion-at=%s:26:13 %s -o - -std=c++2a | FileCheck -check-prefix=CHECK-CC2 %s
   // CHECK-CC2: COMPLETION: t : [#int#]t
 }
 
 // Handle templates
 template <typename T>
 struct Test { T x; };
 template <>
 struct Test<int> {
   int x;
   char y;
 };
 void bar() {
   Test<char> T{.x = 2};
-  // RUN: %clang_cc1 -fsyntax-only -code-completion-patterns -code-completion-at=%s:41:17 %s -o - -std=c++2a | FileCheck -check-prefix=CHECK-CC3 %s
+  // RUN: %clang_cc1 -fsyntax-only -code-completion-patterns -code-completion-at=%s:43:17 %s -o - -std=c++2a | FileCheck -check-prefix=CHECK-CC3 %s
   // CHECK-CC3: COMPLETION: x : [#T#]x
   Test<int> X{.x = 2};
-  // RUN: %clang_cc1 -fsyntax-only -code-completion-patterns -code-completion-at=%s:44:16 %s -o - -std=c++2a | FileCheck -check-prefix=CHECK-CC4 %s
+  // RUN: %clang_cc1 -fsyntax-only -code-completion-patterns -code-completion-at=%s:46:16 %s -o - -std=c++2a | FileCheck -check-prefix=CHECK-CC4 %s
   // CHECK-CC4: COMPLETION: x : [#int#]x
   // CHECK-CC4-NEXT: COMPLETION: y : [#char#]y
 }
 
 template <typename T>
 void aux() {
   Test<T> X{.x = T(2)};
-  // RUN: %clang_cc1 -fsyntax-only -code-completion-patterns -code-completion-at=%s:52:14 %s -o - -std=c++2a | FileCheck -check-prefix=CHECK-CC3 %s
+  // RUN: %clang_cc1 -fsyntax-only -code-completion-patterns -code-completion-at=%s:54:14 %s -o - -std=c++2a | FileCheck -check-prefix=CHECK-CC3 %s
 }