antlr/antlr4 · error · Error

missing interface implementation

Error message

missing interface implementation

What it means

ParseTreePatternMatcher.matchImpl recursively compares a real parse tree against a compiled pattern tree; both must be non-null before any instanceof/structure comparison makes sense. A null tree means the caller asked whether 'nothing' matches a pattern, which is a programming error, so it throws IllegalArgumentException rather than returning false.

Source

Thrown at runtime/JavaScript/src/antlr4/tree/RuleNode.js:10

/* Copyright (c) 2012-2022 The ANTLR Project Contributors. All rights reserved.
 * Use is of this file is governed by the BSD 3-clause license that
 * can be found in the LICENSE.txt file in the project root.
 */
import ParseTree from "./ParseTree.js";

export default class RuleNode extends ParseTree {

    get ruleContext() {
        throw new Error("missing interface implementation")
    }
}

View on GitHub (pinned to 7d5770395b)

Solutions

1. Null-check the tree at the call site: only match after a successful parse produced a tree.
2. Treat parse failure as a distinct outcome (syntax error listener / RecognitionException) instead of proceeding with a null tree.
3. In subclass overrides, validate parameters before delegating to super.matchImpl.

Example fix

// before
boolean ok = matcher.matches(null, "<ID>", R.expr); // tree == null

// after
ParseTree tree = parser.expr();
if (tree == null) return; // handle parse failure separately
boolean ok = matcher.matches(tree, "<ID>", R.expr);

if (tree == null) {
    reportParseFailure();
    return;
}
boolean ok = matcher.matches(tree, patternText, ruleIndex);

boolean isParsed(ParseTree t) { return t != null; }

When it happens

Trigger: Direct calls to the protected matchImpl(tree, patternTree, labels) from a subclass, or a path where the parse result was null (e.g. calling match on a tree reference that was never assigned). Public API matches(tree, pattern, ruleIndex) reaches matchImpl after compiling the pattern, and still throws if tree is null.

Common situations: Custom matcher subclasses overriding or delegating to matchImpl; calling pattern.matcher(null).match(...) because a parser step failed upstream and its null result was not checked.

Related errors

• Fatal error occured while evaluating the names of the gramma
• cannot consume EOF
• index cannot be negative
• Error creating an instanceof the ANTLR tool.
• Dependency analysis failed.

AI-assisted analysis of antlr/antlr4@7d5770395b (2026-08-14). Data as JSON: /api/errors/827c2ced7fd2751c. Report an issue: GitHub.