In-program compiling for unit tests. `preparePluginsFromCompilerOptions` discards `transformProgram` ?

[Griffork]

Hello!

I've been using ts-patch for quite a while now (it's very good) and I've decided to upgrade my usage by creating unit tests for the transformers so that I can verify that they work when new versions of the compiler release.

I am using vitest (though that's not particularly important) and am trying to run the typescript file as an imported script, but I've run into a snag.

It looks like calling the transpileModule function directly in the patched typescript doesn't allow for transformers to run. This appears to be because preparePluginsFromCompilerOptions adds all transformers with a stripped-down config (either just { transform: string } or { transform: string, after: true } but TspPlugin's constructor wants { transform: string, transformProgram: true }.

As preparePluginsFromCompilerOptions is called immediately before new tsp.PluginCreator in tsp's createProgram I don't see a way to change the property of the plugin to allow for program transformers so that my transformers can operate when calling transpileModule.

This is the entire code that I have so far in attempting to do this:

import { MatcherState } from "@vitest/expect";
import Path from "node:path";
import { expect } from "vitest";
import * as ts from "typescript";
import { getTsPackage } from "ts-patch/ts-package.js";
import * as tspatch from "ts-patch/patch/get-patched-source.js";
import * as tsmodule from "ts-patch/module/ts-module.js";

const tsPackage = getTsPackage(Path.join(process.cwd(), "./node_modules/typescript/"));
const tsModule = tsmodule.getTsModule(tsPackage, "typescript.js" as any);
const tspSource = tspatch.getPatchedSource(tsModule, { log: console.log.bind(console) }); 
const tsp: typeof ts = eval(tspSource.js);

const extensions = {
    toCompileTo(this: MatcherState, received: string, expected: string): {message: () => string, pass: boolean} {

        const source = "let x: string  = 'string'";

        let result = tsp.transpileModule(received, { 
            compilerOptions: { 
                module: ts.ModuleKind.ES2022,
                target: ts.ScriptTarget.ES2022,
                strict: true,
                skipLibCheck: true,
                skipDefaultLibCheck: true,
                noErrorTruncation: true,
                noEmitOnError: false,
                experimentalDecorators: true,
                plugins: [
                    { "customTransformers": {after: ["../Compiler/Transformers/MixinTransformer.js"], transformProgram: true } }
                ] as any
            }
        });

        let resultMessage = { message: () => `expected raw code to compile into provided sample (view diff)`, actual: result.outputText.trim(), expected: expected.trim() };

        return {
            ...resultMessage,
            pass: result.outputText.trim() === expected.trim()
        };
    }
};

expect.extend(extensions);

If you have vitest configured it can be called like so:

import { test, expect } from "vitest";

test("Test my custom transformer works", ()=> {
    expect(`some code`).toCompileTo(`some output`);
});

[Griffork]

Neeevermind. Figured it out. Turns out I could just use the SourceTransformers and didn't need the ProgramTransformers.

When calling transpileModule the transformers (as code functions not file paths) should be passed at the top level of the config with the name transformers. Also the transformer will be given context and sourceFile but not program, since I don't use program anyway I just dereference the default object and call the top-level function immediately to unwrap the functions inside which is what transpileModule really wants.

Updated code:

import { MatcherState } from "@vitest/expect";
import Path from "node:path";
import { expect } from "vitest";
import * as ts from "typescript";
import { getTsPackage } from "ts-patch/ts-package.js";
import * as tspatch from "ts-patch/patch/get-patched-source.js";
import * as tsmodule from "ts-patch/module/ts-module.js";

const tsPackage = getTsPackage(Path.join(process.cwd(), "./node_modules/typescript/"));
const tsModule = tsmodule.getTsModule(tsPackage, "typescript.js" as any);
const tspSource = tspatch.getPatchedSource(tsModule, { log: console.log.bind(console) });
const tsp: typeof ts = eval(tspSource.js);

const myTransformer = await import("../Transformers/MyTransformer.js" as any);

const extensions = {
    toCompileTo(this: MatcherState, received: string, expected: string): {message: () => string, pass: boolean} {

        let result = tsp.transpileModule(received, { 
            compilerOptions: { 
                module: ts.ModuleKind.ES2022,
                target: ts.ScriptTarget.ES2022,
                strict: true,
                skipLibCheck: true,
                skipDefaultLibCheck: true,
                noErrorTruncation: true,
                noEmitOnError: false,
                experimentalDecorators: true,
            },
            transformers: {after: [myTransformer.default()] }
        } as any);

        let resultMessage = { message: () => `expected raw code to compile into provided sample (view diff)`, actual: result.outputText.trim(), expected: expected.trim() };

        return {
            ...resultMessage,
            pass: result.outputText.trim() === expected.trim()
        };
    }
};

expect.extend(extensions);

The cool thing is that this code can also be used to create your own custom build script and avoid needing to add your transformers to every project (woo).

Would it be possible to get some API or something for this? Even if it's just a cleaned up version of my hacky stuff that I've written added to the docs on the main page so that others know how to use ts-patch inline.

[Griffork]

Oh also!

/resources/module-patch.ts / .js / .d.ts is not added to the github repository but is referenced by the code. That took me a while to figure out 😅