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Bug: esbuild overwrites the input file despite throwing "Refusing to overwrite input file" #4484
Description
Description
When outdir points to the directory containing the entry point, esbuild throws an error:
Build failed with 1 error: error:
Refusing to overwrite input file error.
However, it still destructively overwrites the original input file with the minified version before/during throwing the error.
Reproduction
Environment
OS: Windows
esbuild version: 0.28.1
Create the following files and run node esbuild.js.
sources/test.js
function test() { console.log( 1 + 1 === 2 ); }
esbuild.js
import fs from 'fs';
import path from 'path';
import esbuild from 'esbuild';
(async function run() {
const basePath = process.cwd();
const sourcePath = path.resolve(basePath, "sources");
const sourceFile = path.resolve(basePath, "sources/test.js");
try {
console.log("Initial source size:", fs.statSync(sourceFile).size, 'bytes');
await esbuild.build({
logLevel: 'silent',
entryPoints: [ sourceFile ],
outdir: sourcePath,
bundle: false,
minify: true,
write: true,
});
} catch (err) {
console.log(err.message);
console.log("Source size after failure:", fs.statSync(sourceFile).size, 'bytes');
}
})();
Actual Behavior
The build fails as expected, but the input file is modified anyway:
Initial source size: 47 bytes
Build failed with 1 error:
error: Refusing to overwrite input file "sources/test.js" (use "allowOverwrite: true" to allow this)
Source size after failure: 33 bytes
The content of sources/test.js becomes minified:
function test(){console.log(!0)}
Expected Behavior
esbuild should abort the write operation and leave the original input file completely untouched if allowOverwrite is not set to true.
Activity
cschanhniem commentedon Jun 19, 2026
I traced the code path. The bug is in
internal/bundler/bundler.go, lines 3094–3121: the overwrite conflict check callslog.AddErrorwith the "Refusing to overwrite" message, but does not remove the conflicting file fromoutputFiles. The slice continues to carry the entry whoseAbsPathmatches a source file.Then in
pkg/api/api_impl.go, lines 1543–1592, the write phase iterates over allresults(which still includes the conflicted entry) and callsioutil.WriteFileon each one — including the one that maps to a source file. By the time the caller checkslog.HasErrors(), the input file has already been overwritten.The fix: in the overwrite-check loop, when a conflict is detected, either:
Contents = nilor mark theAbsPathas excluded) so the write phase skips it, oroutputFilesat the detection site.A minimal patch would be to add
outputFiles[i].AbsPath = ""or similar in the conflict detection block so the write loop at line 1587 skips it. Want me to put together a PR?evanw commentedon Aug 8, 2026
Thanks for reporting this. This is not great. Looks like it regressed in version 0.17.0.
fix evanw#4484: avoid overwriting input files
Update dependency esbuild to v0.28.2 (#2)