Add caching improvement to addExtension API that declares a template does not use the data cascade

[zachleat]

In 11ty/eleventy-plugin-bundle#36 it was surfaced that running esbuild as part of a custom template (in that case through the Render plugin and renderFile) could be improved via memoization if the configuration code can state that no part of the render function relies on the data argument passed in.

eleventyConfig.addExtension("js", {
  outputFileExtension: "js",
  read: false,
  useLayouts: false,
  compile: async (inputContent, inputPath) => {
    const normalizedPath = path.normalize(inputPath);

    // TODO we could memoize here if we know `data` is not being used
    return async (data) => {
      if(!memoized[normalizedPath]) {
        console.log( "esbuilding", normalizedPath );
        memoized[normalizedPath] = esbuild.build({
          // esbuild options truncated
        }).then(output => output.outputFiles[0].text);
      }

      return memoized[normalizedPath];
    };
  },
});

It would be nice to do something like this instead:

eleventyConfig.addExtension("js", {
  outputFileExtension: "js",
  read: false,
  useLayouts: false,
  dataCascade: false, // WARN: this option does not current exist, this is fake
  compile: memoize(async (inputContent, inputPath) => {
    const normalizedPath = path.normalize(inputPath);

    console.log( "esbuilding", normalizedPath );

    // return rendered content directly, not a render function
    return esbuild.build({
      // esbuild options truncated
    }).then(output => output.outputFiles[0].text);
  }),
});