fix!: Behavior of CLI when no arguments are passed

[nzakas]

Prerequisites checklist

• I have read the contributing guidelines.

What is the purpose of this pull request? (put an "X" next to an item)

[x] Documentation update
[x] Bug fix (template)
[ ] New rule (template)
[ ] Changes an existing rule (template)
[ ] Add autofix to a rule
[ ] Add a CLI option
[ ] Add something to the core
[ ] Other, please explain:

What changes did you make? (Give an overview)

When running the CLI without file arguments it silently fails right now. This PR makes the following changes:

• When running the CLI in eslintrc mode, failing to use file arguments throws an error.
• When running the CLI in flat config mode, failing to use file arguments means that it runs on the current working directory.

Fixes #14308

Is there anything you'd like reviewers to focus on?

To make this work, I changed how lintFiles() works in both ESLint and FlatESLint. In FlatESLint, I decided that an empty string and an empty array are the same and should be treated as .. I'm not sure if that's the right decision, so I'd like to hear some opinions on that.

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[mdjermanovic]

I decided that an empty string and an empty array are the same and should be treated as .. I'm not sure if that's the right decision, so I'd like to hear some opinions on that.

Makes sense to me.

[nzakas]

Fixed up the edge cases. I also made it so FlatESLint#lintFiles() doesn't require an argument, and if it's missing, then we use ["."]. This is to have no argument behave the same as "" and [], which makes logical sense to me.

[fasttime]

Let me point out a use case that I think will be negatively impacted by this change. Sometimes people run ESLint only on a subset of files that is calculated dynamically and that could be possibly empty. For example, for performance reasons, some users will want to lint only changed files in a git repo, so they could be running a command like this (reference):

eslint --fix $(git diff --name-only HEAD | xargs)

After this PR, if a user runs the above command while there are no uncommitted changes, the whole current directory will be linted (or they will get an error if eslintrc is used).

[nzakas]

@fasttime for clarification, you're referring to the flat config behavior, which defaults to . and not to the eslintrc behavior, which throws an error.

I assume that ESLint isn't the only tool people are using in this way. There are a lot of tools that default to . when no file arguments are present. How do other tools handle this use case?

[fasttime]

I assume that ESLint isn't the only tool people are using in this way. There are a lot of tools that default to . when no file arguments are present. How do other tools handle this use case?

I'd guess that people are using ESLint like this simply because they were able do it so far. npx prettier prints usage info and exits with an error code. The same happens when I run javac (the Java compiler binary) without arguments. On the other hand, ls without arguments just lists the contents of the current directory, so probably there is no standard way to handle this edge case.

[nzakas]

I think jest works in such a way that you can either pass no arguments or specific tests? Maybe there's some way to set that up for a precommit hook that we can learn from? (I'm not familiar with Jest, so looking for some insights.)

[fasttime]

In fact running jest without arguments prints an error message and exits with an error code:

PS D:\foo> npx jest                  
No tests found, exiting with code 1
Run with `--passWithNoTests` to exit with code 0
In D:\foo
  8 files checked.
  testMatch: **/__tests__/**/*.[jt]s?(x), **/?(*.)+(spec|test).[tj]s?(x) - 0 matches
  testPathIgnorePatterns: \\node_modules\\ - 8 matches
  testRegex:  - 0 matches
Pattern:  - 0 matches

But this behavior can be changed with a flag (--passwithnotests):

PS D:\foo> npx jest --passWithNoTests
No tests found, exiting with code 0

[fasttime]

Maybe there's some way to set that up for a precommit hook that we can learn from?

It seems that lint-staged does not run tasks for glob patterns that don't match any staged file, so at least it shouldn't be a concern for this change.

[nzakas]

Jest is failing without tests because it didn't find any in the directories that it searches by default. It seems like --passwithnotests might be the best thing to copy.

[nzakas]

TSC Summary: This PR changes the default behavior of the ESLint CLI when no file arguments are passed in. In eslintrc mode, the CLI now reports an error; in flat config mode, the CLI now assumes . as the file argument. This may cause a problem for people trying to use the CLI as part of a precommit check. Before this change, the CLI would exit with a zero exit code when no file arguments were present, after this change, it will either error or lint every file, neither of which seems desirable.

TSC Questions:

1. This now looks like a breaking change, should we add it to v9? (This was originally intended to be completed with the flat config work, so it should have been included?)
2. Do we want to provide a way to mimic the current behavior? Jest has a --passwithnotests CLI flag that we could mimic for this purpose.

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[nzakas]

@sam3k please be sure to leave comments as to the resolution from the TSC meeting along with removing the "tsc agenda" label.

[sam3k]

@sam3k please be sure to leave comments as to the resolution from the TSC meeting along with removing the "tsc agenda" label.

Sounds good

[nzakas]

@mdjermanovic this is ready for review