[clang-format] Fix QualifierOrder breaking the code with requires clause.

[curdeius]

Summary

Fixes https://github.com/llvm/llvm-project/issues/53962.

Given the config:

BasedOnStyle: LLVM
QualifierAlignment: Custom
QualifierOrder: ['constexpr', 'type']

The code:

template <typename F>
  requires std::invocable<F>
constexpr constructor();

was incorrectly formatted to:

template <typename F>
  requires 
constexpr std::invocable<F> constructor();

because we considered std::invocable<F> constexpr as a type, not recognising the requires clause.

This patch avoids moving the qualifier across the boundary of the requires clause (checking ClosesRequiresClause).

[HazardyKnusperkeks]

Does it work with a more complex requires clause? Or were they unaffected before? Like Foo<T> && Bar<T>?

[curdeius]

In D120309#3338265, @HazardyKnusperkeks wrote:

Does it work with a more complex requires clause? Or were they unaffected before? Like Foo<T> && Bar<T>?

They were unaffected but I'll add a test.

[curdeius]

Add a test.

clang/lib/Format/QualifierAlignmentFixer.cpp

while (Next && Next->isOneOf(tok::identifier, tok::coloncolon))
       Next = Next->Next;
     if (Next && Next->Previous &&
         Next->Previous->startsSequence(tok::identifier, TT_TemplateOpener)) {
       // Read from to the end of the TemplateOpener to
       // TemplateCloser const ArrayRef<int> a; const ArrayRef<int> &a;
       if (Next->is(tok::comment) && Next->getNextNonComment())
         Next = Next->getNextNonComment();
       assert(Next->MatchingParen && "Missing template closer");
-      Next = Next->MatchingParen->Next;
+      Next = Next->MatchingParen;
+      if (Next->ClosesRequiresClause)
+        return Next;
+      Next = Next->Next;
 
       // Move to the end of any template class members e.g.
       // `Foo<int>::iterator`.
       if (Next && Next->startsSequence(tok::coloncolon, tok::identifier))
         Next = Next->Next->Next;
       if (Next && Next->is(QualifierType)) {
-        // Remove the const.
+        // Move the qualifier.
         insertQualifierBefore(SourceMgr, Fixes, Tok, Qualifier);
         removeToken(SourceMgr, Fixes, Next);
         return Next;
       }
     }
     if (Next && Next->Next &&
         Next->Next->isOneOf(tok::amp, tok::ampamp, tok::star)) {
       if (Next->is(QualifierType)) {
-        // Remove the qualifier.
+        // Move the qualifier.
         insertQualifierBefore(SourceMgr, Fixes, Tok, Qualifier);
         removeToken(SourceMgr, Fixes, Next);
         return Next;
       }
     }
   }
   return Tok;
 }

clang/unittests/Format/QualifierFixerTest.cpp

TEST_F(QualifierFixerTest, QualifierTemplates) {
   verifyFormat("template <class C> using A = /**/ B<Foo<C>, 1>;", Style);
   EXPECT_EQ(ReplacementCount, 0);
   verifyFormat("template <class C>\n"
                "using A = B // foo\n"
                "    <Foo<C>, 1>;",
                Style);
 }
 
+TEST_F(QualifierFixerTest, WithConstraints) {
+  FormatStyle Style = getLLVMStyle();
+  Style.QualifierAlignment = FormatStyle::QAS_Custom;
+  Style.QualifierOrder = {"constexpr", "type"};
+
+  verifyFormat("template <typename T>\n"
+               "  requires Concept<F>\n"
+               "constexpr constructor();",
+               Style);
+  verifyFormat("template <typename T>\n"
+               "  requires Concept1<F> && Concept2<F>\n"
+               "constexpr constructor();",
+               Style);
+}
+
 TEST_F(QualifierFixerTest, DisableRegions) {
   FormatStyle Style = getLLVMStyle();
   Style.QualifierAlignment = FormatStyle::QAS_Custom;
   Style.QualifierOrder = {"inline", "static", "const", "type"};
 
   ReplacementCount = 0;
   verifyFormat("// clang-format off\n"
                "int const inline static a = 0;\n"