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camc314
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## Summary Preserve source maps when `strip-ts` removes TypeScript-only printer regions from JS builds. The plugin now uses Rolldown’s `magicString` transform context instead of a plain string replacement, so removed `/* IF TS */` regions retain correct mappings back to the original printer source.
76 lines
2.6 KiB
TypeScript
76 lines
2.6 KiB
TypeScript
import type { Plugin } from "rolldown";
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/**
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* Plugin to remove the TypeScript-only regions of `print.ts` from the JS-only builds.
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*
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* The `TS` build-time constant (see `src-js/globals.d.ts`) lets the minifier drop TS-only code
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* in expression positions - `if (TS && node.declare)` folds to nothing when `TS` is `false`.
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* But `case "TSEnumDeclaration":` switch arms are not expressions, and no minifier can remove an arm
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* on the grounds that its node type never occurs. Those arms are fenced with `IF TS` / `END_IF`
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* block-comment markers (the same convention as the raw transfer deserializer builds):
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*
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* ```ts
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* /* IF TS *\/
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* case "TSEnumDeclaration":
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* ...
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* break;
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* /* END_IF *\/
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* ```
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*
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* (`*\/` escapes above only because this is itself a block comment.)
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*
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* This plugin deletes everything from each `IF TS` marker line through its `END_IF` marker line.
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* Once the arms are gone, the TS-only printer functions they called lose their last references,
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* and tree-shaking removes them wholesale.
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*
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* It's a plain text transform (the fences are only visible in source text), so it must run before
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* the AST-based plugins in the plugin list, and only in builds where `TS` is `false`.
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*/
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const REGION = /[ \t]*\/\* IF TS \*\/\n[\s\S]*?\/\* END_IF \*\/\n/g;
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// A factory, so each build counts its own regions rather than sharing a total with the others
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const stripTsPlugin = (): Plugin => {
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let strippedRegions = 0;
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return {
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name: "strip-ts",
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buildStart() {
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strippedRegions = 0;
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},
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transform: {
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// Only process TS files in `src-js/print` directory
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filter: { id: /\/src-js\/print\/.+\.ts$/ },
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handler(code, _path, meta) {
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const magicString = meta.magicString!;
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for (const match of code.matchAll(REGION)) {
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strippedRegions++;
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const start = match.index!;
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magicString.remove(start, start + match[0].length);
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}
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const transformed = magicString.toString();
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// Unbalanced or nested fences leave a marker behind.
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// Most files have no fences at all, so the "did this plugin do anything" check is per build, in `buildEnd`.
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if (transformed.includes("IF TS") || transformed.includes("END_IF")) {
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throw new Error("strip-ts: unbalanced or nested `/* IF TS */` / `/* END_IF */` fences");
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}
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return { code: magicString };
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},
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},
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buildEnd() {
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// No fences anywhere means they have been lost and this plugin is silently doing nothing
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if (strippedRegions === 0) {
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throw new Error("strip-ts: no `/* IF TS */` / `/* END_IF */` fences found");
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}
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},
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};
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};
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export default stripTsPlugin;
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