[IDE] Loosen assertion check in IDE/SyntaxModelWalker

We were asserting that the attribute range recorded in the AST started at the
same location as the fist unconsumed SyntaxNode in the file. This should be
true in most cases, but isn't for mispelled attributes, corrected in the AST
but not recognised or present in the list of SyntaxNodes. E.g.
@Availability(...) comes through as if @available(...) was specified, but
there's no SyntaxNode for it because we don't highlight invalid attributes
(to indicate they're invalid).

Resolves rdar://problem/62201594
Resolves https://bugs.swift.org/browse/SR-12500

Author: Nathan Hawes

lib/IDE/SyntaxModel.cpp

@@ -1214,7 +1214,13 @@ bool ModelASTWalker::handleSpecialDeclAttribute(const DeclAttribute *D,
         if (!passNode({SyntaxNodeKind::AttributeBuiltin, Next.Range}))
           return false;
       } else {
-          assert(0 && "Attribute's TokenNodes already consumed?");
+        // Only mispelled attributes, corrected in the AST but not
+        // recognised or present in TokenNodes should get us here.
+        // E.g. @availability(...) comes through as if @available(...) was
+        // specified, but there's no TokenNode because we don't highlight them
+        // (to indicate they're invalid).
+        assert(Next.Range.getStart() == D->getRange().Start &&
+               "Attribute's TokenNodes already consumed?");
       }
     } else {
         assert(0 && "No TokenNodes?");

test/IDE/coloring.swift

@@ -554,3 +554,8 @@ struct FreeWhere<T> {
   // CHECK: <kw>typealias</kw> Alias = <type>Int</type> <kw>where</kw> <type>T</type> == <type>Int</type>
   typealias Alias = Int where T == Int
 }
+
+// Renamed attribute ('fixed' to @available by the parser after emitting an error, so not treated as a custom attribute)
+// CHECK: @availability(<kw>macOS</kw> <float>10.11</float>, *)
+@availability(macOS 10.11, *)
+class HasMisspelledAttr {}