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feat: Use Rolldown native MagicString #846

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feat: Use Rolldown native MagicString #846

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5e5506b
feat: Use Rolldown native `MagicString`
timfish Jan 20, 2026
5f8d7a5
Merge branch 'main' into timfish/feat/rolldown-magic-string
timfish Jan 23, 2026
3190a92
Add docs link
timfish Jan 23, 2026
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29 changes: 24 additions & 5 deletions packages/bundler-plugin-core/src/index.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -232,10 +232,12 @@ type RenderChunkHook = (
chunk: {
fileName: string;
facadeModuleId?: string | null;
}
},
outputOptions?: unknown,
meta?: { magicString?: MagicString }
) => {
code: string;
map: SourceMap;
readonly map?: SourceMap;
} | null;

/**
Expand Down Expand Up @@ -292,7 +294,12 @@ export function createRollupInjectionHooks(
renderChunk: RenderChunkHook;
} {
return {
renderChunk(code: string, chunk: { fileName: string; facadeModuleId?: string | null }) {
renderChunk(
code: string,
chunk: { fileName: string; facadeModuleId?: string | null },
_?: unknown,
meta?: { magicString?: MagicString }
) {
if (!isJsFile(chunk.fileName)) {
return null; // returning null means not modifying the chunk at all
}
Expand Down Expand Up @@ -320,7 +327,7 @@ export function createRollupInjectionHooks(
}
}

const ms = new MagicString(code, { filename: chunk.fileName });
const ms = meta?.magicString || new MagicString(code, { filename: chunk.fileName });
const match = code.match(COMMENT_USE_STRICT_REGEX)?.[0];

if (match) {
Expand All @@ -333,9 +340,21 @@ export function createRollupInjectionHooks(
ms.prepend(codeToInject);
}

// Rolldown can pass a native MagicString instance in meta.magicString
// https://rolldown.rs/in-depth/native-magic-string#usage-examples
if (ms?.constructor?.name === "BindingMagicString") {
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@logaretm logaretm Jan 23, 2026 •
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q: could this check fail in the future since this is experimental? we could check meta.magicString again here instead. WDYT?

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@timfish timfish Jan 23, 2026 •
edited
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We only want to return { code: magicStringInstance as string } if this is a Rolldown native instance. The value of meta.magicString doesn't matter at this point.

// Rolldown docs say to return the magic string instance directly in this case
return { code: ms as unknown as string };
}

return {
code: ms.toString(),
map: ms.generateMap({ file: chunk.fileName, hires: "boundary" }),
get map() {
return ms.generateMap({
file: chunk.fileName,
hires: "boundary",
});
},
};
},
};
Expand Down
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