Memory leak in typescript plugin (4.0.0+)

[Tronil]

• Rollup Plugin Name: typescript
• Rollup Plugin Version: 4.1.1
• Rollup Version: 2.6.1
• Operating System (or Browser): Linux
• Node Version: 12.16.2

How Do We Reproduce?

Clone https://github.com/Tronil/rollup-ts-mem-leak
Run:
npm install
npm run watch
Repeatedly trigger watch build by saving src/index.ts

Expected Behavior

Memory usage should not grow until rollup crashes with out-of-memory.

Actual Behavior

Memory usage grows with about 25MB for every triggered build, eventually running out of memory and crashing.

Note that this repo only contains a "hello world" file - for real projects this memory leak is massive. In our project the leak was around 300 MB for every build, making the process crash after 6 or 7 builds. The 3.x versions do not appear to have this issue, so it is likely related to the 4.0 rewrite.

[shellscape]

Have you verified that it's a problem with that plugin specifically and not rollup core?

[Tronil]

If I use version 3.1.1 of the typescript plugin, the memory leak seems to disappear - so I assume the leak is in the plugin. Also the leak did not appear before adding the typescript plugin (our project was originally in pure javascript).

[Tronil]

Looked through the source and this part caught my eye:

buildStart() {
      emitParsedOptionsErrors(ts, this, parsedOptions);

      program = createWatchProgram(ts, this, {
        formatHost,
        resolveModule,
        parsedOptions,
        writeFile(fileName, data) {
          emittedFiles.set(fileName, data);
        }
      });
    },

program is being replaced every time buildStart() is called, which looks a little odd. After I put in a check for whether it is already set, the leak disappears...
So this seems to fix it:

buildStart() {
      emitParsedOptionsErrors(ts, this, parsedOptions);
      if (!program) {
        program = createWatchProgram(ts, this, {
          formatHost,
          resolveModule,
          parsedOptions,
          writeFile(fileName, data) {
            emittedFiles.set(fileName, data);
          }
        });
      }
    },

[NotWoods]

Would you be interested in submitting a PR with the change? Otherwise I can add it in later.

[Tronil]

I don't know when I'll have some time to look at a PR, so I wouldn't wait for me to create one.

[VitorLuizC]

I can make this PR.