Don't treat class name contextToken as a completion list blocker if it is not the previousToken (#21534)

src/services/completions.ts

@@ -1921,7 +1921,8 @@ namespace ts.Completions {
             return isDeclarationName(contextToken)
                 && !isJsxAttribute(contextToken.parent)
                 // Don't block completions if we're in `class C /**/`, because we're *past* the end of the identifier and might want to complete `extends`.
-                && !(isClassLike(contextToken.parent) && position > previousToken.end);
+                // If `contextToken !== previousToken`, this is `class C ex/**/`.
+                && !(isClassLike(contextToken.parent) && (contextToken !== previousToken || position > previousToken.end));
         }
 
         function isFunctionLikeButNotConstructor(kind: SyntaxKind) {

tests/cases/fourslash/completionsKeywordsExtends.ts

@@ -1,6 +1,7 @@
 /// <reference path="fourslash.ts" />
 
 ////class C/*a*/ /*b*/ { }
+////class C e/*c*/ {}
 
 // Tests that `isCompletionListBlocker` is true *at* the class name, but false *after* it.
 
@@ -9,3 +10,6 @@ verify.completionListIsEmpty();
 
 goTo.marker("b");
 verify.completionListContains("extends");
+
+goTo.marker("c");
+verify.completionListContains("extends");