Fix bug: Allow completions after '@' with no contextToken (#27325)

Author: Andy

src/services/completions.ts

@@ -43,7 +43,7 @@ namespace ts.Completions {
         }
 
         const contextToken = findPrecedingToken(position, sourceFile);
-        if (triggerCharacter && (!contextToken || !isValidTrigger(sourceFile, triggerCharacter, contextToken, position))) return undefined;
+        if (triggerCharacter && !isValidTrigger(sourceFile, triggerCharacter, contextToken, position)) return undefined;
 
         if (isInString(sourceFile, position, contextToken)) {
             return !contextToken || !isStringLiteralLike(contextToken)
@@ -2272,7 +2272,7 @@ namespace ts.Completions {
         return !!type.getStringIndexType() || !!type.getNumberIndexType();
     }
 
-    function isValidTrigger(sourceFile: SourceFile, triggerCharacter: CompletionsTriggerCharacter, contextToken: Node, position: number): boolean {
+    function isValidTrigger(sourceFile: SourceFile, triggerCharacter: CompletionsTriggerCharacter, contextToken: Node | undefined, position: number): boolean {
         switch (triggerCharacter) {
             case ".":
             case "@":
@@ -2281,14 +2281,14 @@ namespace ts.Completions {
             case "'":
             case "`":
                 // Only automatically bring up completions if this is an opening quote.
-                return isStringLiteralOrTemplate(contextToken) && position === contextToken.getStart(sourceFile) + 1;
+                return !!contextToken && isStringLiteralOrTemplate(contextToken) && position === contextToken.getStart(sourceFile) + 1;
             case "<":
                 // Opening JSX tag
-                return contextToken.kind === SyntaxKind.LessThanToken && (!isBinaryExpression(contextToken.parent) || binaryExpressionMayBeOpenTag(contextToken.parent));
+                return !!contextToken && contextToken.kind === SyntaxKind.LessThanToken && (!isBinaryExpression(contextToken.parent) || binaryExpressionMayBeOpenTag(contextToken.parent));
             case "/":
-                return isStringLiteralLike(contextToken)
+                return !!contextToken && (isStringLiteralLike(contextToken)
                     ? !!tryGetImportFromModuleSpecifier(contextToken)
-                    : contextToken.kind === SyntaxKind.SlashToken && isJsxClosingElement(contextToken.parent);
+                    : contextToken.kind === SyntaxKind.SlashToken && isJsxClosingElement(contextToken.parent));
             default:
                 return Debug.assertNever(triggerCharacter);
         }

tests/cases/fourslash/completionsTriggerCharacter.ts

@@ -2,6 +2,7 @@
 
 // @jsx: preserve
 
+/////** @/*tag*/ */
 //////</*comment*/
 ////const x: "a" | "b" = "/*openQuote*/"/*closeQuote*/;
 ////const y: 'a' | 'b' = '/*openSingleQuote*/'/*closeSingleQuote*/;
@@ -29,6 +30,7 @@
 ////const divide = 1 //*divide*/
 
 verify.completions(
+    { marker: "tag", includes: ["param"], triggerCharacter: "@" },
     { marker: "comment", exact: undefined, triggerCharacter: "<" },
 
     { marker: "openQuote", exact: ["a", "b"], triggerCharacter: '"' },