using --fail-on-changes does not create stash and discards all unstaged changes from partially staged file

[movy]

I am just starting with lint-staged, and instantly hit this issue :( Luckily, I was experimenting on a small change and was able to recover my losses from VSCode file history. This is not related to VSCode per se, as repro below is done purely from command line and produced the same outcome.

The most basic config:

"*.{js,jsx}": "eslint"

git version 2.34.1

Repro steps:

• stage a single line from a file, to make staged version trigger linting error
• run npx lint-staged --fail-on-changes
• surprisingly, lint-staged fails, despite our config witheslint without --fix flag
• ALL unstaged changes to the staged file are GONE. And stash is not created!

Running without --fail-on-changes flag works fine, but I would not want unverified linter's modifications in my repo, so really want to make this work.

Full log is below.

p.s. In addition, I also managed to wipe out ALL unstaged changes to all files when ran npx lint-staged --fail-on-changes --hide-unstaged. As those changes included freshly installed lint-staged config, it ended up with a very vanilla error message from git: No valid configuration found, which defo can be improved (example of confusion: desktop/desktop#16870). I have also checked #1657 and #1402, and do not think my case falls into those.

Repro log:

$ git status    
Changes not staged for commit:
        modified:   bots/restart-trading.js

### STAGED SINGLE LINE from restart-trading.js to produce linting error on staged code

$ git status
Changes to be committed:
        modified:   bots/restart-trading.js

Changes not staged for commit:
        modified:   bots/restart-trading.js

$ npx lint-staged --fail-on-changes
✔ Backed up original state in git stash (b3adf7b5)
✔ Hiding unstaged changes to partially staged files...
⚠ Running tasks for staged files...
  ❯ package.json — 1 file
    ❯ *.{js,jsx} — 1 file
      ✖ eslint [FAILED]
    ↓ *.mjs — no files
    ↓ **/*.ts?(x) — no files
✖ Tasks modified files and --fail-on-changes was used!
↓ Skipped because of errors from tasks.
✔ Cleaning up temporary files...

✖ lint-staged failed because `--fail-on-changes` was used.

✖ eslint:
(node:2632900) ExperimentalWarning: Importing JSON modules is an experimental feature and might change at any time
(Use `node --trace-warnings ...` to show where the warning was created)

/home/ubuntu/jesse-bot/bots/restart-trading.js
  260:35  error  'maxUptime' is not defined  no-undef
  393:24  error  'maxUptime' is not defined  no-undef

✖ 2 problems (2 errors, 0 warnings)

$ git status
Changes to be committed:
        modified:   bots/restart-trading.js

### ALL UNSTAGED CHANGES ARE GONE!!!

$ git stash show
No stash entries found.

[iiroj]

Thanks for the issue. This feature is new so there might be some oversight I made. You see the commit hash in the logs so maybe git show b3adf7b5 still works.

Can you run lint-staged --debug so that we can see the debug logs?

[iiroj]

From this it looks like the we should be skipping the cleanup on errors when using --fail-on-changes:

↓ Skipped because of errors from tasks.
✔ Cleaning up temporary files...

[movy]

My bad, overlooked --debug option, here's verbose log:

$ git status
Changes to be committed:
        modified:   bots/restart-trading.js

Changes not staged for commit:
        modified:   bots/restart-trading.js



$ npx lint-staged --debug  --fail-on-changes
lint-staged:bin: Using shell: /usr/bin/zsh +4ms
lint-staged:bin: Options parsed from command-line: {
  allowEmpty: false,
  concurrent: true,
  configPath: undefined,
  continueOnError: false,
  cwd: undefined,
  debug: true,
  diff: undefined,
  diffFilter: undefined,
  failOnChanges: true,
  hidePartiallyStaged: true,
  hideUnstaged: false,
  maxArgLength: undefined,
  quiet: false,
  relative: false,
  revert: false,
  stash: true,
  verbose: false
} +1ms
lint-staged: Running `lint-staged@16.2.1` on Node.js v22.11.0 (linux) +6ms
lint-staged:execGit: Running git command [ 'version', '--build-options' ] +51ms
lint-staged: git version 2.34.1
cpu: x86_64
no commit associated with this build
sizeof-long: 8
sizeof-size_t: 8
shell-path: /bin/sh +8ms
lint-staged:validateOptions: Validating options... +15ms
lint-staged:validateOptions: Validated options: {
  allowEmpty: false,
  color: true,
  concurrent: true,
  configObject: undefined,
  configPath: undefined,
  continueOnError: false,
  cwd: undefined,
  debug: true,
  diff: undefined,
  diffFilter: undefined,
  failOnChanges: true,
  hidePartiallyStaged: true,
  hideUnstaged: false,
  maxArgLength: 65536,
  quiet: false,
  relative: false,
  revert: false,
  stash: true,
  verbose: false
} +0ms
lint-staged: Unset GIT_LITERAL_PATHSPECS (was `undefined`) +0ms
lint-staged:runAll: Running all linter scripts... +16ms
lint-staged:runAll: Using working directory `/home/ubuntu/jesse-bot` +0ms
lint-staged:resolveGitRepo: Resolving git repo from `/home/ubuntu/jesse-bot` +50ms
lint-staged:resolveGitRepo: Unset GIT_DIR (was `undefined`) +0ms
lint-staged:resolveGitRepo: Unset GIT_WORK_TREE (was `undefined`) +0ms
lint-staged:execGit: Running git command [ 'rev-parse', '--show-cdup', '--show-toplevel', '--absolute-git-dir' ] +10ms
lint-staged:resolveGitRepo: Resolved git repository top-level directory to be `/home/ubuntu/jesse-bot` +3ms
lint-staged:resolveGitRepo: Resolved git config directory to be `/home/ubuntu/jesse-bot/.git` +0ms
lint-staged:execGit: Running git command [ 'log', '-1' ] +4ms
lint-staged:execGit: Running git command [ 'diff', '--diff-filter=ACMR', '--staged', '--raw', '-z' ] +5ms
lint-staged:searchConfigs: Searching for configuration files... +26ms
lint-staged:execGit: Running git command [
  'ls-files',
  '-z',
  '--full-name',
  '-t',
  '--cached',
  '--others',
  '--exclude-standard',
  '--',
  ':(glob)**/package.json',
  ':(glob)**/package.yaml',
  ':(glob)**/package.yml',
  ':(glob)**/.lintstagedrc',
  ':(glob)**/.lintstagedrc.json',
  ':(glob)**/.lintstagedrc.yaml',
  ':(glob)**/.lintstagedrc.yml',
  ':(glob)**/.lintstagedrc.mjs',
  ':(glob)**/.lintstagedrc.mts',
  ':(glob)**/.lintstagedrc.js',
  ':(glob)**/.lintstagedrc.ts',
  ':(glob)**/.lintstagedrc.cjs',
  ':(glob)**/.lintstagedrc.cts',
  ':(glob)**/lint-staged.config.mjs',
  ':(glob)**/lint-staged.config.mts',
  ':(glob)**/lint-staged.config.js',
  ':(glob)**/lint-staged.config.ts',
  ':(glob)**/lint-staged.config.cjs',
  ':(glob)**/lint-staged.config.cts'
] +0ms
lint-staged:searchConfigs: Listing possible configs from filesystem starting from "/home/ubuntu/jesse-bot"... +0ms
lint-staged:searchConfigs: Found possible config files from filesystem: [ '/home/ubuntu/jesse-bot/package.json' ] +11ms
lint-staged:searchConfigs: Found possible config files from git: [
  '/home/ubuntu/jesse-bot/package.json'
] +14ms
lint-staged:loadConfig: Loading configuration from `/home/ubuntu/jesse-bot/package.json`... +0ms
lint-staged:loadConfig: Successfully loaded config from `/home/ubuntu/jesse-bot/package.json`:
{
  '*.{js,jsx}': 'eslint',
  '*.mjs': 'eslint',
  '**/*.ts?(x)': 'tsc -p tsconfig.json --noEmit'
} +0ms
lint-staged:validateConfig: Validating config from `/home/ubuntu/jesse-bot/package.json`... +64ms
lint-staged:validateConfig: Validated config from `/home/ubuntu/jesse-bot/package.json`: +0ms
lint-staged:validateConfig: {
  '*.{js,jsx}': 'eslint',
  '*.mjs': 'eslint',
  '**/*.ts?(x)': 'tsc -p tsconfig.json --noEmit'
} +0ms
lint-staged:searchConfigs: Found 1 config files +11ms
lint-staged:runAll: Loaded list of staged files in git:
[
  {
    filepath: '/home/ubuntu/jesse-bot/bots/restart-trading.js',
    status: 'M'
  }
] +49ms
lint-staged:groupFilesByConfig: Grouping 1 files by 1 configurations +99ms
lint-staged:chunkFiles: Resolved an argument string length of 46 characters from 1 files +109ms
lint-staged:chunkFiles: Creating 1 chunks for maxArgLength of 65536 +0ms
lint-staged:generateTasks: Generating linter tasks +100ms
lint-staged:generateTasks: Generated task: 
{
  pattern: '*.{js,jsx}',
  commands: 'eslint',
  fileList: [
    {
      filepath: '/home/ubuntu/jesse-bot/bots/restart-trading.js',
      status: 'M'
    }
  ]
} +2ms
lint-staged:generateTasks: Generated task: 
{ pattern: '*.mjs', commands: 'eslint', fileList: [] } +0ms
lint-staged:generateTasks: Generated task: 
{
  pattern: '**/*.ts?(x)',
  commands: 'tsc -p tsconfig.json --noEmit',
  fileList: []
} +0ms
lint-staged:getSpawnedTasks: Creating Listr tasks for commands 'eslint' +103ms
lint-staged:getSpawnedTask: cmd: eslint +104ms
lint-staged:getSpawnedTask: args: [] +0ms
lint-staged:getSpawnedTask: Spawn options: {
  cwd: '/home/ubuntu/jesse-bot',
  preferLocal: true,
  stdin: 'ignore',
  env: { FORCE_COLOR: 'true' }
} +0ms
lint-staged:getSpawnedTasks: Creating Listr tasks for commands 'eslint' +0ms
lint-staged:getSpawnedTask: cmd: eslint +0ms
lint-staged:getSpawnedTask: args: [] +0ms
lint-staged:getSpawnedTask: Spawn options: {
  cwd: '/home/ubuntu/jesse-bot',
  preferLocal: true,
  stdin: 'ignore',
  env: { FORCE_COLOR: 'true' }
} +0ms
lint-staged:getSpawnedTasks: Creating Listr tasks for commands 'tsc -p tsconfig.json --noEmit' +0ms
lint-staged:getSpawnedTask: cmd: tsc +0ms
lint-staged:getSpawnedTask: args: [ '-p', 'tsconfig.json', '--noEmit' ] +0ms
lint-staged:getSpawnedTask: Spawn options: {
  cwd: '/home/ubuntu/jesse-bot',
  preferLocal: true,
  stdin: 'ignore',
  env: { FORCE_COLOR: 'true' }
} +0ms
lint-staged:chunkFiles: Resolved an argument string length of 46 characters from 1 files +4ms
lint-staged:chunkFiles: Creating 1 chunks for maxArgLength of 65536 +0ms
lint-staged:runAll: Set max event listeners to the number of tasks: 3 +6ms
[STARTED] Backing up original state...
lint-staged:GitWorkflow: Backing up original state... +106ms
lint-staged:GitWorkflow: Backing up merge state... +0ms
lint-staged:file: Reading file `/home/ubuntu/jesse-bot/.git/MERGE_HEAD` +106ms
lint-staged:file: Reading file `/home/ubuntu/jesse-bot/.git/MERGE_MODE` +0ms
lint-staged:file: Reading file `/home/ubuntu/jesse-bot/.git/MERGE_MSG` +0ms
lint-staged:file: File `/home/ubuntu/jesse-bot/.git/MERGE_HEAD` doesn't exist, ignoring... +0ms
lint-staged:file: File `/home/ubuntu/jesse-bot/.git/MERGE_MODE` doesn't exist, ignoring... +0ms
lint-staged:file: File `/home/ubuntu/jesse-bot/.git/MERGE_MSG` doesn't exist, ignoring... +0ms
lint-staged:GitWorkflow: Done backing up merge state! +0ms
lint-staged:GitWorkflow: Getting deleted files... +0ms
lint-staged:execGit: Running git command [ 'ls-files', '--deleted' ] +46ms
lint-staged:GitWorkflow: Found deleted files: [] +5ms
lint-staged:GitWorkflow: Getting partially staged files... +0ms
lint-staged:execGit: Running git command [ 'status', '-z' ] +5ms
lint-staged:GitWorkflow: Found partially staged files: [ 'bots/restart-trading.js' ] +18ms
lint-staged:execGit: Running git command [
  'diff',
  '--binary',
  '--unified=0',
  '--no-color',
  '--no-ext-diff',
  '--src-prefix=a/',
  '--dst-prefix=b/',
  '--patch',
  '--submodule=short',
  '--output',
  '/home/ubuntu/jesse-bot/.git/lint-staged_unstaged.patch',
  '--',
  'bots/restart-trading.js'
] +19ms
lint-staged:execGit: Running git command [ 'stash', 'create' ] +23ms
lint-staged:execGit: Running git command [ 'rev-parse', '--short', 'b2a29bbe82c5c000311a0f4a98beba9ef28d2178' ] +70ms
lint-staged:execGit: Running git command [
  'stash',
  'store',
  '--quiet',
  '--message',
  'lint-staged automatic backup',
  'b2a29bbe'
] +4ms
lint-staged:GitWorkflow: Backed up original state in git stash (b2a29bbe) +104ms
lint-staged:GitWorkflow: Calculating SHA-256 hash of unstaged changes because "--fail-on-changes" was used... +0ms
lint-staged:execGit: Running git command [ 'diff', '--patch', '--unified=0' ] +5ms
lint-staged:GitWorkflow: SHA-256 hash of unstaged changes is %S 11097a5b57ded0995a34d41f49646889f02162edb48d80108624447cb23949e1 +29ms
[COMPLETED] Backed up original state in git stash (b2a29bbe)
[STARTED] Hiding unstaged changes to partially staged files...
lint-staged:execGit: Running git command [ 'checkout', '--force', '--', 'bots/restart-trading.js' ] +30ms
[COMPLETED] Hiding unstaged changes to partially staged files...
[STARTED] Running tasks for staged files...
[STARTED] package.json — 1 file
[STARTED] *.{js,jsx} — 1 file
[STARTED] *.mjs — 0 files
[STARTED] **/*.ts?(x) — 0 files
[SKIPPED] *.mjs — no files
[SKIPPED] **/*.ts?(x) — no files
[STARTED] eslint
lint-staged:getSpawnedTask: Failed to list child processes of pid "437947": Error: No matching pid found
    at /home/ubuntu/jesse-bot/node_modules/pidtree/lib/pidtree.js:61:16
    at /home/ubuntu/jesse-bot/node_modules/pidtree/lib/ps.js:40:7
    at ChildProcess.<anonymous> (/home/ubuntu/jesse-bot/node_modules/pidtree/lib/bin.js:57:5)
    at ChildProcess.emit (node:events:518:28)
    at maybeClose (node:internal/child_process:1104:16)
    at ChildProcess._handle.onexit (node:internal/child_process:304:5) {
  [stack]: [Getter/Setter],
  [message]: 'No matching pid found'
} +5014ms
[FAILED] eslint [FAILED]
[FAILED] eslint [FAILED]
[COMPLETED] Running tasks for staged files...
[STARTED] Applying modifications from tasks...
lint-staged:GitWorkflow: Calculating SHA-256 hash of changes after tasks because "--fail-on-changes" was used... +4854ms
lint-staged:execGit: Running git command [ 'diff', '--patch', '--unified=0' ] +4853ms
lint-staged:GitWorkflow: SHA-256 hash of changes after tasks is %S undefined +18ms
[FAILED] Tasks modified files and --fail-on-changes was used!
[STARTED] Restoring unstaged changes...
[SKIPPED] Skipped because of errors from tasks.
[STARTED] Cleaning up temporary files...
lint-staged:GitWorkflow: Dropping backup stash... +0ms
lint-staged:execGit: Running git command [ 'stash', 'list', '--format="%h %s"', '-z' ] +19ms
lint-staged:execGit: Running git command [ 'stash', 'drop', '--quiet', '0' ] +5ms
lint-staged:GitWorkflow: Done dropping backup stash! +18ms
[COMPLETED] Cleaning up temporary files...

✖ lint-staged failed because `--fail-on-changes` was used.

✖ eslint:
(node:437947) ExperimentalWarning: Importing JSON modules is an experimental feature and might change at any time
(Use `node --trace-warnings ...` to show where the warning was created)

/home/ubuntu/jesse-bot/bots/restart-trading.js
  260:35  error  'maxUptime' is not defined  no-undef
  393:24  error  'maxUptime' is not defined  no-undef

✖ 2 problems (2 errors, 0 warnings)

$ git status
On branch main
Your branch is up to date with 'origin/main'.

Changes to be committed:
        modified:   bots/restart-trading.js

$ 

[iiroj]

I'll make some changes so that:

1. backup stash won't be dropped when using --fail-on-changes and there are errors
2. when using --no-revert (also implied by --fail-on-changes), we can still restore unstaged changes that were hidden
3. the stash restoration example is printed in this scenario

% node bin/lint-staged.js --fail-on-changes
✔ Backed up original state in git stash (8e70df7f)
✔ Running tasks for staged files...
✖ Tasks modified files and --fail-on-changes was used!
↓ Cleaning up temporary files...

✖ lint-staged failed because `--fail-on-changes` was used.

Any lost modifications can be restored from a git stash:

  > git stash list --format="%h %s"
  h0a0s0h0 On main: lint-staged automatic backup
  > git apply --index h0a0s0h0

[iiroj]

Regarding this:

As those changes included freshly installed lint-staged config, it ended up with a very vanilla error message from git: No valid configuration found.

That error message is from lint-staged and not Git itself. I agree that it's confusing when this happens to the lint-staged config file, but not sure how to improve given the file is stored in Git just like any other. Sometimes I think it would be better to just support fewer features so that it's not possible to end up in extreme combos like this, with lint-staged hiding its own configuration file changes.

[iiroj]

Let's hope v16.2.2 works better for you, thanks for the issue!

[movy]

Regarding this:

As those changes included freshly installed lint-staged config, it ended up with a very vanilla error message from git: No valid configuration found.

That error message is from lint-staged and not Git itself. I agree that it's confusing when this happens to the lint-staged config file, but not sure how to improve given the file is stored in Git just like any other. Sometimes I think it would be better to just support fewer features so that it's not possible to end up in extreme combos like this, with lint-staged hiding its own configuration file changes.

I think, at least the error message can be improved to make it more useful to end user:

• state clear that it's coming from lint-staged;
• offer some debug info about paths where config was not found.

Something like this:
No valid configuration found -> lint-staged: No valid configuration found in the following locations: ...

[movy]

I'll make some changes so that:

1. backup stash won't be dropped when using --fail-on-changes and there are errors
2. when using --no-revert (also implied by --fail-on-changes), we can still restore unstaged changes that were hidden
3. the stash restoration example is printed in this scenario

If I understand correctly, whenever --fail-on-changes is triggered, the stash won't be restored automatically and the user is supposed to notice disappeared unstaged changes and restore it manually?

Also, any idea why --fail-on-changes triggers when eslint is called w/o --fix-all flag? I assumed it should not change any files in such case, just report errors...

[iiroj]

Ok that makes a bit of sense. My assumption has been that when running the lint-staged process and its stderr has some content, it would be obvious it comes from lint-staged. but it wouldn't hurt to adjust the message like:

✖ lint-staged could not find any valid configuration.

[iiroj]

I see the issue wrt. hashing in your debug logs:

Before running tasks:

lint-staged:GitWorkflow: SHA-256 hash of unstaged changes is %S 11097a5b57ded0995a34d41f49646889f02162edb48d80108624447cb23949e1 +29ms
[COMPLETED] Backed up original state in git stash (b2a29bbe)
[STARTED] Hiding unstaged changes to partially staged files...

After running tasks:

lint-staged:execGit: Running git command [ 'diff', '--patch', '--unified=0' ] +4853ms
lint-staged:GitWorkflow: SHA-256 hash of changes after tasks is %S undefined +18ms

So I guess hiding the partially staged changes mean the diff is different before/after, and lint-staged detects these as changes.

Maybe I should move the hashing to happen after hiding the changes.

EDIT: I have accidentally debug-logged this.diffSha256 instead of diffSha256 so can't be 100% sure of the value, but this would still explain it.

[iiroj]

@movy ok, v16.2.3 should handle the diffing correctly. 👍