Windows git "warning: LF will be replaced by CRLF", is that warning tail backward?

warning: LF will be replaced by CRLF.

Depending on the editor you are using, a text file with LF wouldn't necessary be saved with CRLF: recent editors can preserve eol style. But that git config setting insists on changing those...

Simply make sure that (as I recommend here):

git config --global core.autocrlf false

That way, you avoid any automatic transformation, and can still specify them through a .gitattributes file and core.eol directives.

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windows git "LF will be replaced by CRLF"
Is this warning tail backward?

No: you are on Windows, and the git config help page does mention

Use this setting if you want to have CRLF line endings in your working directory even though the repository does not have normalized line endings.

As described in "git replacing LF with CRLF", it should only occur on checkout (not commit), with core.autocrlf=true.

       repo
    /        \ 
crlf->lf    lf->crlf 
 /              \    

As mentioned in XiaoPeng's answer, that warning is the same as:

warning: (If you check it out/or clone to another folder with your current core.autocrlf configuration,) LF will be replaced by CRLF
The file will have its original line endings in your (current) working directory.

As mentioned in git-for-windows/git issue 1242:

I still feel this message is confusing, the message could be extended to include a better explanation of the issue, for example: "LF will be replaced by CRLF in file.json after removing the file and checking it out again".

Note: Git 2.19 (Sept 2018), when using core.autocrlf, the bogus "LF will be replaced by CRLF" warning is now suppressed.

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As quaylar rightly comments, if there is a conversion on commit, it is to LF only.

That specific warning "LF will be replaced by CRLF" comes from convert.c#check_safe_crlf():

if (checksafe == SAFE_CRLF_WARN)
  warning("LF will be replaced by CRLF in %s.
           The file will have its original line endings 
           in your working directory.", path);
else /* i.e. SAFE_CRLF_FAIL */
  die("LF would be replaced by CRLF in %s", path);

It is called by convert.c#crlf_to_git(), itself called by convert.c#convert_to_git(), itself called by convert.c#renormalize_buffer().

And that last renormalize_buffer() is only called by merge-recursive.c#blob_unchanged().

So I suspect this conversion happens on a git commit only if said commit is part of a merge process.

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Note: with Git 2.17 (Q2 2018), a code cleanup adds some explanation.

See commit 8462ff4 (13 Jan 2018) by Torsten Bögershausen (tboegi).
^{(Merged by Junio C Hamano -- gitster -- in commit 9bc89b1, 13 Feb 2018)}

convert_to_git(): safe_crlf/checksafe becomes int conv_flags

When calling convert_to_git(), the checksafe parameter defined what should happen if the EOL conversion (CRLF --> LF --> CRLF) does not roundtrip cleanly.
In addition, it also defined if line endings should be renormalized (CRLF --> LF) or kept as they are.

checksafe was an safe_crlf enum with these values:

SAFE_CRLF_FALSE:       do nothing in case of EOL roundtrip errors
SAFE_CRLF_FAIL:        die in case of EOL roundtrip errors
SAFE_CRLF_WARN:        print a warning in case of EOL roundtrip errors
SAFE_CRLF_RENORMALIZE: change CRLF to LF
SAFE_CRLF_KEEP_CRLF:   keep all line endings as they are

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Note that a regression introduced in 8462ff4 ("convert_to_git(): safe_crlf/checksafe becomes int conv_flags", 2018-01-13, Git 2.17.0) back in Git 2.17 cycle caused autocrlf rewrites to produce a warning message despite setting safecrlf=false.

See commit 6cb0912 (04 Jun 2018) by Anthony Sottile (asottile).
^{(Merged by Junio C Hamano -- gitster -- in commit 8063ff9, 28 Jun 2018)}

YES the warning is backwards.

And in fact it shouldn't even be a warning in the first place. Because all this warning is saying (but backwards unfortunately) is that the CRLF characters in your file with Windows line endings will be replaced with LF's on commit. Which means it's normalized to the same line endings used by *nix and MacOS.

Nothing strange is going on, this is exactly the behavior you would normally want.

This warning in it's current form is one of two things:

1. An unfortunate bug combined with an over-cautious warning message, or
2. A very clever plot to make you really think this through...

;)

--Update on 9th July---

Removed "It is correct and accurate" as commented by @mgiuca

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NO. It is NOT talking about your files currently with CRLF. It is instead talking about files with LF.

It should read:

warning: (If you check it out/or clone to another folder with your current core.autocrlf configuration,)LF will be replaced by CRLF

The file will have its original line endings in your (current) working directory.

This picture should explain what it means.