[clang-format] Annotate noexcept, explicit specifiers as containing expressions

[rymiel]

Summary

The noexcept specifier and explicit specifier can optionally include a
boolean expression to make these specifiers apply conditionally,
however, clang-format didn't set the context for the parenthesized
content of these specifiers, meaning they inherited the parent context,
which usually isn't an expressions, leading to misannotated binary
operators.

This patch applies expression context to the content of these
specifiers, making them similar to the static_assert keyword.

Fixes https://github.com/llvm/llvm-project/issues/44543

[owenpan]

Should we add tests to TokenAnnotatorTest.cpp?

[rymiel]

Yes, good point, I will do that

[rymiel]

Annotator tests (copied from format tests)

clang/lib/Format/TokenAnnotator.cpp

bool parseParens(bool LookForDecls = false) {
     } else if (Style.isJavaScript() &&
                (Line.startsWith(Keywords.kw_type, tok::identifier) ||
                 Line.startsWith(tok::kw_export, Keywords.kw_type,
                                 tok::identifier))) {
       // type X = (...);
       // export type X = (...);
       Contexts.back().IsExpression = false;
     } else if (OpeningParen.Previous &&
-               (OpeningParen.Previous->isOneOf(tok::kw_static_assert,
-                                               tok::kw_while, tok::l_paren,
-                                               tok::comma, TT_BinaryOperator) ||
+               (OpeningParen.Previous->isOneOf(
+                    tok::kw_static_assert, tok::kw_noexcept, tok::kw_explicit,
+                    tok::kw_while, tok::l_paren, tok::comma,
+                    TT_BinaryOperator) ||
                 OpeningParen.Previous->isIf())) {
       // static_assert, if and while usually contain expressions.
       Contexts.back().IsExpression = true;
     } else if (Style.isJavaScript() && OpeningParen.Previous &&
                (OpeningParen.Previous->is(Keywords.kw_function) ||
                 (OpeningParen.Previous->endsSequence(tok::identifier,
                                                      Keywords.kw_function)))) {
       // function(...) or function f(...)

clang/unittests/Format/FormatTest.cpp

TEST_F(FormatTest, UnderstandsRvalueReferences) {
   verifyIndependentOfContext("A<int &&, int &&> a;");
   verifyGoogleFormat("A<int&&> a;");
   verifyGoogleFormat("A<int&&, int&&> a;");
 
   // Not rvalue references:
   verifyFormat("template <bool B, bool C> class A {\n"
                "  static_assert(B && C, \"Something is wrong\");\n"
                "};");
+  verifyFormat("template <typename T> void swap() noexcept(Bar<T> && Foo<T>);");
+  verifyFormat("template <typename T> struct S {\n"
+               "  explicit(Bar<T> && Foo<T>) S(const S &);\n"
+               "};");
   verifyGoogleFormat("#define IF(a, b, c) if (a && (b == c))");
   verifyGoogleFormat("#define WHILE(a, b, c) while (a && (b == c))");
   verifyFormat("#define A(a, b) (a && b)");
 }
 
 TEST_F(FormatTest, FormatsBinaryOperatorsPrecedingEquals) {
   verifyFormat("void f() {\n"
                "  x[aaaaaaaaa -\n"

clang/unittests/Format/TokenAnnotatorTest.cpp

TEST_F(TokenAnnotatorTest, UnderstandsUsesOfStarAndAmp) {
   EXPECT_TOKEN(Tokens[12], tok::amp, TT_BinaryOperator);
   EXPECT_TOKEN(Tokens[17], tok::amp, TT_PointerOrReference);
 
   Tokens = annotate("struct S {\n"
                     "  auto Mem = C & D;\n"
                     "}");
   ASSERT_EQ(Tokens.size(), 12u) << Tokens;
   EXPECT_TOKEN(Tokens[7], tok::amp, TT_BinaryOperator);
+
+  Tokens =
+      annotate("template <typename T> void swap() noexcept(Bar<T> && Foo<T>);");
+  ASSERT_EQ(Tokens.size(), 23u) << Tokens;
+  EXPECT_TOKEN(Tokens[15], tok::ampamp, TT_BinaryOperator);
+
+  Tokens = annotate("template <typename T> struct S {\n"
+                    "  explicit(Bar<T> && Foo<T>) S(const S &);\n"
+                    "};");
+  ASSERT_EQ(Tokens.size(), 30u) << Tokens;
+  EXPECT_TOKEN(Tokens[14], tok::ampamp, TT_BinaryOperator);
 }
 
 TEST_F(TokenAnnotatorTest, UnderstandsUsesOfPlusAndMinus) {
   auto Tokens = annotate("x - 0");
   ASSERT_EQ(Tokens.size(), 4u) << Tokens;
   EXPECT_TOKEN(Tokens[1], tok::minus, TT_BinaryOperator);
   Tokens = annotate("0 + 0");
   ASSERT_EQ(Tokens.size(), 4u) << Tokens;