plandex-ai/plandex · error

failed to parse the content with fallback parser: %v

Error message

failed to parse the content with fallback parser: %v

What it means

When the primary parse produces a tree with errors, ValidateWithParsers retries with a fallback parser. If the fallback ParseCtx also fails or returns a nil tree — excluding timeout-like errors, which are reported as TimedOut — it returns 'failed to parse the content with fallback parser: %v'. This means neither the primary nor the fallback grammar could parse the content.

Source

Thrown at app/server/syntax/validate.go:68

		}

		return nil, fmt.Errorf("failed to parse the content: %v", err)
	}
	defer tree.Close()

	// Get the root node of the syntax tree and check for errors
	root := tree.RootNode()

	if root.HasError() {
		if fallbackParser != nil {
			fallbackTree, err := fallbackParser.ParseCtx(ctx, nil, []byte(file))
			if err != nil || fallbackTree == nil {

				if err != nil && strings.Contains(err.Error(), "timeout") {
					return &ValidationRes{Lang: lang, Parser: parser, TimedOut: true}, nil
				}

				return nil, fmt.Errorf("failed to parse the content with fallback parser: %v", err)
			}
			defer fallbackTree.Close()

			root = fallbackTree.RootNode()

			if !root.HasError() {
				return &ValidationRes{Lang: fallbackLang, Parser: fallbackParser, Valid: true}, nil
			}
		}

		errorMarkers := insertErrorMarkers(file, root)

		return &ValidationRes{
			Lang:   lang,
			Parser: parser,
			Valid:  false,
			Errors: errorMarkers,
		}, nil

View on GitHub (pinned to e2d772072e)

Solutions

1. Read the wrapped '%v' cause; fix cancellation/deadline issues by enlarging the context
2. Confirm content is syntactically valid for the target language; fix the source syntax
3. Skip fallback validation or treat the file as unparseable and exclude it
4. Update grammars/parsers to a version that supports the language constructs used

Example fix

// before
res, err := syntax.ValidateFile(path, content)
// after
ctx, cancel := context.WithTimeout(context.Background(), 60*time.Second)
defer cancel()
res, err := syntax.ValidateFile(path, content, syntax.WithContext(ctx))

if ctx == nil || ctx.Err() != nil {
    return fmt.Errorf("context dead before fallback parse")
}
primaryRes, err := ValidateWithParsers(lang, content, primaryParsers)
if err == nil && primaryRes != nil && !primaryRes.ParseHasError {
    return nil // no fallback needed
}

res, err := ValidateFile(path, content)
if err != nil && strings.Contains(err.Error(), "fallback parser") {
    if strings.Contains(err.Error(), "timeout") {
        res = &syntax.ValidationRes{TimedOut: true}
    } else {
        log.Printf("content unparseable by any grammar: %v", err)
    }
}

When it happens

Trigger: Primary parse yields a tree whose root HasError, the fallback parser is attempted, and the fallback parse errors for a non-timeout reason (cancellation, nil tree, internal failure) during ValidateFile/validateSyntax/loadBuildFile.

Common situations: Content valid under neither the primary nor fallback grammar; context deadline expiring between the two parses; fallback parser not actually initialized (nil-related failure); content for a language with weak grammar support.

Understand the failure class

• Parsing and encoding errors: unexpected token, malformed input — why parsers reject input and how to find the real culprit.

Related errors

• failed to parse the content: %v
• error validating original file syntax: %v
• failed to parse the original content: %v
• failed to parse the proposed content: %v
• invalid context index: %s

AI-assisted analysis of plandex-ai/plandex@e2d772072e (2026-09-05). Data as JSON: /api/errors/af1d52986fe0903d. Report an issue: GitHub.