[clang][CodeComplete] Make completion work after initializer lists

[kadircet]

Summary

CodeCompletion was not being triggered after successfully parsed
initializer lists, e.g.

cpp
void foo(int, bool);
void bar() {
  foo({1}^, false);
}

CodeCompletion would suggest the function foo as an overload candidate up until
the point marked with ^ but after that point we do not trigger signature help
since parsing succeeds.

This patch handles that case by failing in parsing expression lists whenever we
see a codecompletion token, in addition to getting an invalid subexpression.

[merge_guards_bot]

Unit tests: pass. 62094 tests passed, 0 failed and 785 were skipped.

clang-tidy: unknown.

clang-format: pass.

Build artifacts: diff.json, clang-format.patch, CMakeCache.txt, console-log.txt, test-results.xml

[kadircet]

• Add comments

[merge_guards_bot]

Unit tests: pass. 62094 tests passed, 0 failed and 785 were skipped.

clang-tidy: unknown.

clang-format: pass.

Build artifacts: diff.json, clang-format.patch, CMakeCache.txt, console-log.txt, test-results.xml

clang/lib/Parse/ParseExpr.cpp

while (1) {
     if (getLangOpts().CPlusPlus11 && Tok.is(tok::l_brace)) {
       Diag(Tok, diag::warn_cxx98_compat_generalized_initializer_lists);
       Expr = ParseBraceInitializer();
     } else
       Expr = ParseAssignmentExpression();
 
     if (Tok.is(tok::ellipsis))
       Expr = Actions.ActOnPackExpansion(Expr.get(), ConsumeToken());
+    else if (Tok.is(tok::code_completion)) {
+      // There's nothing to suggest in here as we parsed a full expression.
+      // Instead fail and propogate the error since caller might have something
+      // the suggest, e.g. signature help in function call. Note that this is
+      // performed before pushing the \p Expr, so that signature help can report
+      // current argument correctly.
+      SawError = true;
+      cutOffParsing();
+      break;
+    }
     if (Expr.isInvalid()) {
       SkipUntil(tok::comma, tok::r_paren, StopBeforeMatch);
       SawError = true;
     } else {
       Exprs.push_back(Expr.get());
     }
 
     if (Tok.isNot(tok::comma))

clang/test/CodeCompletion/call.cpp

void test() {
   // RUN: %clang_cc1 -fsyntax-only -code-completion-patterns -code-completion-at=%s:19:9 %s -o - | FileCheck -check-prefix=CHECK-CC1 %s
   // CHECK-CC1: f(Y y, <#int ZZ#>)
   // CHECK-CC1-NEXT: f(int i, <#int j#>, int k)
   // CHECK-CC1-NEXT: f(float x, <#float y#>)
   // CHECK-CC1: COMPLETION: Pattern : dynamic_cast<<#type#>>(<#expression#>)
   // RUN: %clang_cc1 -fsyntax-only -code-completion-at=%s:19:13 %s -o - | FileCheck -check-prefix=CHECK-CC2 %s
   // CHECK-CC2-NOT: f(Y y, int ZZ)
   // CHECK-CC2: f(int i, int j, <#int k#>)
+  f({}, 0, 0);
+  // RUN: %clang_cc1 -fsyntax-only -code-completion-patterns -code-completion-at=%s:28:7 %s -o - | FileCheck -check-prefix=CHECK-CC3 %s
+  // CHECK-CC3: OVERLOAD: [#void#]f()
+  // CHECK-CC3-NEXT: OVERLOAD: [#void#]f(<#X#>)
+  // CHECK-CC3-NEXT: OVERLOAD: [#void#]f(<#int i#>, int j, int k)
+  // CHECK-CC3-NEXT: OVERLOAD: [#void#]f(<#float x#>, float y)
 }