[clangd] Enable hover on character literal.

[hokein]

Summary

In the initial hover expression patch (https://reviews.llvm.org/D72500), we
disabled all literals.

There is some value on running hover on character literals (e.g. see the
int value of the char).

[hokein]

clang-tools-extra/clangd/Hover.cpp

744

there may be some value to enable StringLiteral as well (e.g. see the length of the string), but it seems to work partially:

• auto char_ptr = "ab^c"; // fails
• char abc[] = "a^bc"; // works
• const char* ptr = "a^bc"; // fails"
• "a^bc"; // fails
• func("a^bc"); // fails

Looks like the reason is that EvaluateAsRValue fails on a lvalue StringLiteral. It'd require a bit of work to make it useful for common cases.

[hokein]

friendly ping, I think it would be nice to get it in before 14 release.

[kadircet]

thanks, lgtm!

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

1254

s/,/;

clang-tools-extra/clangd/Hover.cpp

HoverInfo getDeducedTypeHoverContents(QualType QT, const syntax::Token &Tok,
   }
 
   return HI;
 }
 
 bool isLiteral(const Expr *E) {
   // Unfortunately there's no common base Literal classes inherits from
   // (apart from Expr), therefore these exclusions.
-  return llvm::isa<CharacterLiteral>(E) || llvm::isa<CompoundLiteralExpr>(E) ||
+  return llvm::isa<CompoundLiteralExpr>(E) ||
          llvm::isa<CXXBoolLiteralExpr>(E) ||
          llvm::isa<CXXNullPtrLiteralExpr>(E) ||
          llvm::isa<FixedPointLiteral>(E) || llvm::isa<FloatingLiteral>(E) ||
          llvm::isa<ImaginaryLiteral>(E) || llvm::isa<IntegerLiteral>(E) ||
          llvm::isa<StringLiteral>(E) || llvm::isa<UserDefinedLiteral>(E);
 }
 
 llvm::StringLiteral getNameForExpr(const Expr *E) {
   // FIXME: Come up with names for `special` expressions.
   //
   // It's an known issue for GCC5, https://godbolt.org/z/Z_tbgi. Work around
   // that by using explicit conversion constructor.
   //

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

llvm::StringRef Tests[] = {
             };
             class Bar {};
             constexpr Foo s = ^{
               .xyz = Bar(),
             };
           )cpp",
       // literals
       "auto x = t^rue;",
-      "auto x = '^A';",
       "auto x = ^(int){42};",
       "auto x = ^42.;",
       "auto x = ^42.0i;",
       "auto x = ^42;",
       "auto x = ^nullptr;",
       "auto x = ^\"asdf\";",
   };
 
TEST(Hover, NoHover) {
   }
 }
 
 TEST(Hover, All) {
   struct {
     const char *const Code;
     const std::function<void(HoverInfo &)> ExpectedBuilder;
   } Cases[] = {
+      {"auto x = [['^A']]; // character literal",
+       [](HoverInfo &HI) {
+         HI.Name = "expression", HI.Type = "char";
+         HI.Value = "65 (0x41)";
+       }},
       {
           R"cpp(// Local variable
             int main() {
               int bonjour;
               ^[[bonjour]] = 2;
               int test1 = bonjour;
             }
           )cpp",