Modifying buffer output in onEnd callback doesn't update text output

[ArnaudBarre]

Following #1792

Repro

version: 0.14.51

const { build } = require("esbuild");

build({
  write: false,
  stdin: { contents: "const a = 1;" },
  plugins: [
    {
      name: "updateOutput",
      setup: (build) => {
        build.onEnd((result) => {
          const file = result.outputFiles[0];
          const transformed = file.text.replace("1", "2");
          file.contents = Buffer.from(transformed);
          // Object.defineProperty(file, "text", { value: transformed });
        });
      },
    },
  ],
}).then((result) => {
  const file = result.outputFiles[0];
  console.log(file.contents.toString().trim(), file.text.trim());
});

Result

Logs const a = 2; const a = 1;

Expected result

Logs const a = 2; const a = 2;

Workaround

Uncommenting the defineProperty line gives the expected result.

[evanw]

This is not a feature. There is nothing in the documentation that says this is supposed to work. I recommend calling Object.defineProperty as you suggested.

[ArnaudBarre]

I agree this not documented that it should work as simply as this, but this is what I expected when reading It can modify the build result in this section and seeing that text was a getter.

Would you accept a PR for:

1. Adding a small paragraph to document how to modify build result (i.e. setting both text and contents like above)
2. Update convertOutputFiles to

function convertOutputFiles({ path, contents }: protocol.BuildOutputFile): types.OutputFile {
  let text: string | null = null;
  let mutableContents = contents;
  return {
    path,
    get contents() {
      return mutableContents;
    },
    set contents(value) {
      mutableContents = value;
      text = null
    },
    get text() {
      if (text === null) text = protocol.decodeUTF8(mutableContents);
      return text;
    },
    set text(value) {
      text = value;
      mutableContents = protocol.encodeUTF8(value)
    },
  }
}

[ArnaudBarre]

Thanks for the change. I understand the performance reason for not having a setter for text, but this not obvious at first that this is only a getter. This could be made clearer by adding a small precision in the doc like: It can modify the build result (by mutating `contents`) and adding a readonly modifier for text on the TS types.

[evanw]

Changing the type of text on the TS types makes sense to do, but people would likely complain if I did that because it's a backwards-incompatible type change. I'll try to remember to do that with the next breaking change release.

[ArnaudBarre]

Having a TS error because some part of your code didn't make sense is not a breaking change IMO because it doesn't break you code (.i.e nothing change at runtime) and you can just add an ts-ignore comment. But I understand that for a project of that size there is always people complaining