[Scope map] Cope with extensions that have bogus {} locations.

Author: DougGregor

lib/AST/ASTScope.cpp

@@ -1420,9 +1420,14 @@ SourceRange ASTScope::getSourceRangeImpl() const {
     return typeDecl->getSourceRange();
 
   case ASTScopeKind::ExtensionGenericParams: {
-    // The generic parameters of an extension are available from the trailing
+    // The generic parameters of an extension are available from the ':' of
+    // the inheritance clause (if available), or else that from the
     // 'where' (if present) or from the start of the body.
+    // FIXME: Approximating the ':' with the start of the first inherited entry.
     SourceLoc startLoc;
+    if (!extension->getInherited().empty() &&
+        extension->getInherited().front().getSourceRange().Start.isValid())
+      startLoc = extension->getInherited().front().getSourceRange().Start;
     if (auto trailingWhere = extension->getTrailingWhereClause())
       startLoc = trailingWhere->getWhereLoc();
     else
@@ -1807,7 +1812,13 @@ SmallVector<ValueDecl *, 4> ASTScope::getLocalBindings() const {
     // No local declarations.
     break;
 
-  case ASTScopeKind::ExtensionGenericParams:
+  case ASTScopeKind::ExtensionGenericParams: {
+    // If the source range containing the extension parameters is empty,
+    // do nothing.
+    SourceRange range = getSourceRangeImpl();
+    if (range.Start == range.End)
+      break;
+
     // Bind this extension, if we haven't done so already.
     if (!extension->getExtendedType())
       if (auto resolver = extension->getASTContext().getLazyResolver())
@@ -1821,6 +1832,7 @@ SmallVector<ValueDecl *, 4> ASTScope::getLocalBindings() const {
         result.push_back(param);
     }
     break;
+  }
 
   case ASTScopeKind::GenericParams:
     result.push_back(genericParams.params->getParams()[genericParams.index]);

test/NameBinding/scope_map_lookup.swift

@@ -112,6 +112,10 @@ protocol Fooable {
   var foo: Foo { get }
 }
 
+// The extension below once caused infinite recursion.
+struct S<T> // expected-error{{expected '{' in struct}}
+extension S // expected-error{{expected '{' in extension}}
+
 let a = b ; let b = a // expected-error{{could not infer type for 'a'}} 
 // expected-error@-1 {{'a' used within its own type}}
 // FIXME: That second error is bogus.