fix(linter/plugins): do not call before hook if empty visitor

[overlookmotel]

If rule is defined using createOnce, and it returns an empty visitor (before / after hooks only), then don't run the hooks - the rule is a no-op.

Reason this is important is forward-compatibility with an optimization we could make where we calculate on Rust side whether AST contains any nodes that rules act on, and if it doesn't, skip calling into JS entirely. In that case, the before hook wouldn't run on those files.

We can't emulate that behavior entirely, but we can at least avoid users creating rules which only contain a before hook, and then finding that when we apply that optimization later on, it stops behaving as expected.

i.e. we make the before hook never be called for a rule defined like this:

export default {
  createOnce(context) {
    return {
      before() {
        if (content.filename.endsWith('.tsx') {
          context.report({ message: 'No TSX!', node: context.sourceCode.ast });
        }
      },
    };
  },
};

To get a rule to always run on every file:

export default {
  createOnce(context) {
    return {
-     before() {
+     Program(_node) {
        if (content.filename.endsWith('.tsx') {
          context.report({ message: 'No TSX!', node: context.sourceCode.ast });
        }
      },
    };
  },
};

[overlookmotel]

• fix(linter/plugins): do not call before hook if empty visitor #14401 👈 (View in Graphite)
• main

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[Copilot]

Pull Request Overview

This PR optimizes the linter plugin system by preventing the execution of before and after hooks when a rule's visitor is empty (contains no AST node visitor functions). This improves forward compatibility with planned Rust-side optimizations that may skip JavaScript execution entirely for files that don't contain relevant AST nodes.

• Adds logic to detect empty visitors and substitute a no-op before hook that always returns false
• Updates test fixtures to ensure rules with only hooks have at least one AST visitor function to maintain their expected behavior
• Removes expected test output for rules that now correctly skip hook execution

Reviewed Changes

Copilot reviewed 13 out of 13 changed files in this pull request and generated 1 comment.

File	Description
apps/oxlint/src-js/plugins/load.ts	Implements the core optimization logic to detect empty visitors and prevent hook execution
apps/oxlint/test/fixtures/*/plugin.ts	Updates test rules to include AST visitor functions to maintain expected test behavior
apps/oxlint/test/fixtures/*/output.snap.md	Removes expected output for hooks that are now correctly skipped
apps/oxlint/test/fixtures/*/.oxlintrc.json	Adds configuration for new test rule

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[overlookmotel]

Merge activity

• Oct 7, 9:42 AM UTC: The merge label '0-merge' was detected. This PR will be added to the Graphite merge queue once it meets the requirements.
• Oct 7, 9:42 AM UTC: overlookmotel added this pull request to the Graphite merge queue.
• Oct 7, 9:48 AM UTC: Merged by the Graphite merge queue.