Only indent Objective-C method declarations (swiftlang#860)

This prevents bugs where the indentation formatting code is mistakenly executed
with declarations that are not Objective-C methods, like certain C++ functions.

Resolves: rdar://129590639

Author: mportiz08

src/utils/indentation.js

@@ -10,7 +10,18 @@
 
 import Language from 'docc-render/constants/Language';
 
+const ObjcMethodPrefix = {
+  instance: '-',
+  klass: '+',
+};
+
 function indentObjcDeclaration(codeElement) {
+  // only attempt to indent declarations for Objective-C instance/class methods
+  const txt = codeElement.textContent ?? '';
+  if (!txt.startsWith(ObjcMethodPrefix.instance) && !txt.startsWith(ObjcMethodPrefix.klass)) {
+    return;
+  }
+
   // find all param name spans (which are tokenized as "token-identifier"s)
   const params = codeElement.getElementsByClassName('token-identifier');
   if (params.length < 2) {

tests/unit/utils/indentation.spec.js

@@ -59,5 +59,16 @@ describe('indentDeclaration', () => {
         expect(code.innerHTML).toEqual(originalCode);
       });
     });
+
+    describe('with a C++ function that has namespaced parameters', () => {
+      it('should not add indentation', () => {
+        const originalCode = '<a href="/documentation/mycppclass" class="type-identifier-link"><code><span>MyCPPClass</span></code></a><span class="token-identifier">operator+</span>(<span class="token-identifier">std</span>::<span class="type-identifier-link"><span>string</span></span> <span class="token-internalParam">other</span>);';
+
+        const code = prepare(originalCode);
+        indentDeclaration(code, 'occ');
+
+        expect(code.innerHTML).toEqual(originalCode);
+      });
+    });
   });
 });