[Format/ObjC] Correctly handle base class with lightweight generics and protocol

[benhamilton]

Summary

ClangFormat does not correctly handle an Objective-C interface declaration
with both lightweight generics and a protocol conformance.

This simple example:

@interface Foo : Bar <Baz> <Blech>

@end

means Foo extends Bar (a lightweight generic class whose type
parameter is Baz) and also conforms to the protocol Blech.

ClangFormat should not apply any changes to the above example, but
instead it currently formats it quite poorly:

@interface Foo : Bar <Baz>
<Blech>

    @end

The bug is that UnwrappedLineParser assumes an open-angle bracket
after a base class name is a protocol list, but it can also be a
lightweight generic specification.

This diff fixes the bug by factoring out the logic to parse
lightweight generics so it can apply both to the declared class
as well as the base class.

Test Plan: New tests added. Ran tests with:

% ninja FormatTests && ./tools/clang/unittests/Format/FormatTests
Confirmed tests failed before diff and passed after diff.

[MyDeveloperDay]

LGTM

clang/lib/Format/UnwrappedLineParser.h

private:
   void parseNew();
   void parseAccessSpecifier();
   bool parseEnum();
   void parseJavaEnumBody();
   // Parses a record (aka class) as a top level element. If ParseAsExpr is true,
   // parses the record as a child block, i.e. if the class declaration is an
   // expression.
   void parseRecord(bool ParseAsExpr = false);
+  void parseObjCLightweightGenerics();
   void parseObjCMethod();
   void parseObjCProtocolList();
   void parseObjCUntilAtEnd();
   void parseObjCInterfaceOrImplementation();
   bool parseObjCProtocol();
   void parseJavaScriptEs6ImportExport();
   void parseStatementMacro();
   void parseCSharpAttribute();

clang/lib/Format/UnwrappedLineParser.cpp

void UnwrappedLineParser::parseObjCInterfaceOrImplementation() {
   assert(FormatTok->Tok.getObjCKeywordID() == tok::objc_interface ||
          FormatTok->Tok.getObjCKeywordID() == tok::objc_implementation);
   nextToken();
   nextToken(); // interface name
 
   // @interface can be followed by a lightweight generic
   // specialization list, then either a base class or a category.
   if (FormatTok->Tok.is(tok::less)) {
-    // Unlike protocol lists, generic parameterizations support
-    // nested angles:
-    //
-    // @interface Foo<ValueType : id <NSCopying, NSSecureCoding>> :
-    //     NSObject <NSCopying, NSSecureCoding>
-    //
-    // so we need to count how many open angles we have left.
-    unsigned NumOpenAngles = 1;
-    do {
-      nextToken();
-      // Early exit in case someone forgot a close angle.
-      if (FormatTok->isOneOf(tok::semi, tok::l_brace) ||
-          FormatTok->Tok.isObjCAtKeyword(tok::objc_end))
-        break;
-      if (FormatTok->Tok.is(tok::less))
-        ++NumOpenAngles;
-      else if (FormatTok->Tok.is(tok::greater)) {
-        assert(NumOpenAngles > 0 && "'>' makes NumOpenAngles negative");
-        --NumOpenAngles;
-      }
-    } while (!eof() && NumOpenAngles != 0);
-    nextToken(); // Skip '>'.
+    parseObjCLightweightGenerics();
   }
   if (FormatTok->Tok.is(tok::colon)) {
     nextToken();
     nextToken(); // base class name
+    // The base class can also have lightweight generics applied to it.
+    if (FormatTok->Tok.is(tok::less)) {
+      parseObjCLightweightGenerics();
+    }
   } else if (FormatTok->Tok.is(tok::l_paren))
     // Skip category, if present.
     parseParens();
 
   if (FormatTok->Tok.is(tok::less))
     parseObjCProtocolList();
 
   if (FormatTok->Tok.is(tok::l_brace)) {
     if (Style.BraceWrapping.AfterObjCDeclaration)
       addUnwrappedLine();
     parseBlock(/*MustBeDeclaration=*/true);
   }
 
   // With instance variables, this puts '}' on its own line.  Without instance
   // variables, this ends the @interface line.
   addUnwrappedLine();
 
   parseObjCUntilAtEnd();
 }
 
+void UnwrappedLineParser::parseObjCLightweightGenerics() {
+  assert(FormatTok->Tok.is(tok::less));
+  // Unlike protocol lists, generic parameterizations support
+  // nested angles:
+  //
+  // @interface Foo<ValueType : id <NSCopying, NSSecureCoding>> :
+  //     NSObject <NSCopying, NSSecureCoding>
+  //
+  // so we need to count how many open angles we have left.
+  unsigned NumOpenAngles = 1;
+  do {
+    nextToken();
+    // Early exit in case someone forgot a close angle.
+    if (FormatTok->isOneOf(tok::semi, tok::l_brace) ||
+        FormatTok->Tok.isObjCAtKeyword(tok::objc_end))
+      break;
+    if (FormatTok->Tok.is(tok::less))
+      ++NumOpenAngles;
+    else if (FormatTok->Tok.is(tok::greater)) {
+      assert(NumOpenAngles > 0 && "'>' makes NumOpenAngles negative");
+      --NumOpenAngles;
+    }
+  } while (!eof() && NumOpenAngles != 0);
+  nextToken(); // Skip '>'.
+}
+
 // Returns true for the declaration/definition form of @protocol,
 // false for the expression form.
 bool UnwrappedLineParser::parseObjCProtocol() {
   assert(FormatTok->Tok.getObjCKeywordID() == tok::objc_protocol);
   nextToken();
 
   if (FormatTok->is(tok::l_paren))
     // The expression form of @protocol, e.g. "Protocol* p = @protocol(foo);".

clang/unittests/Format/FormatTestObjC.cpp

verifyFormat("@interface Foo<Baz : Blech> : Bar <Baz, Quux> {\n"
                "@end");
 
   verifyFormat("@interface Foo<Bar : Baz <Blech>> : Xyzzy <Corge> {\n"
                "  int _i;\n"
                "}\n"
                "+ (id)init;\n"
                "@end");
 
+  verifyFormat("@interface Foo<Bar : Baz <Blech>> : Xyzzy <Corge> <Quux> {\n"
+               "  int _i;\n"
+               "}\n"
+               "+ (id)init;\n"
+               "@end");
+
+  verifyFormat("@interface Foo : Bar <Baz> <Blech>\n"
+               "@end");
+
+  verifyFormat("@interface Foo : Bar <Baz> <Blech, Xyzzy, Corge>\n"
+               "@end");
+
   verifyFormat("@interface Foo (HackStuff) {\n"
                "  int _i;\n"
                "}\n"
                "+ (id)init;\n"
                "@end");
 
   verifyFormat("@interface Foo () {\n"
                "  int _i;\n"
verifyFormat("void eeeeeeee(int eeeee, int eeeee,\n"
                "              int eeeee, int eeeee);\n");
   // ObjCBinPackProtocolList should be BPS_Never by default.
   verifyFormat("@interface fffffffffffff () <\n"
                "    fffffffffffff,\n"
                "    fffffffffffff,\n"
                "    fffffffffffff,\n"
                "    fffffffffffff> {\n"
                "}");
+  verifyFormat("@interface ggggggggggggg\n"
+               "    : ggggggggggggg <ggggggggggggg>\n"
+               "      <ggggggggggggg>\n"
+               "@end");
 }
 
 TEST_F(FormatTestObjC, FormatObjCImplementation) {
   verifyFormat("@implementation Foo : NSObject {\n"
                "@public\n"
                "  int field1;\n"
                "@protected\n"
                "  int field2;\n"