Is it possible for git-merge to ignore line-ending differences?

Update 2013:

More recent git versions authorize using merge with strategy recursive and strategy option (-X):

• from “Git Merge and Fixing Mixed Spaces and Tabs with two Branches“:

  git merge -s recursive -Xignore-space-at-eol
  

But using “-Xignore-space-change” is also a possibility

• Fab-V mentions below:

  git merge master -s recursive -X renormalize
  

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jakub.g also comments that the strategies work also with cherry-picking:

git cherry-pick abcd123456 --strategy=recursive --strategy-option=renormalize 

This works much better than ignore-all-space.

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Before Git 2.29 (Q4 2020), All “mergy” operations that internally use the merge-recursive machinery should honor the merge.renormalize configuration, but many of them didn’t.

See commit 00906d6, commit 8d55225, commit 6f6e7cf, commit fe48efb (03 Aug 2020) by Elijah Newren (newren).
^{(Merged by Junio C Hamano — gitster — in commit 4339259, 10 Aug 2020)}

merge: make merge.renormalize work for all uses of merge machinery

^{Signed-off-by: Elijah Newren}

The ‘merge‘ command is not the only one that does merges; other commands like checkout -m or rebase do as well.

Unfortunately, the only area of the code that checked for the “merge.renormalize” config setting was in builtin/merge.c, meaning it could only affect merges performed by the “merge” command.

Move the handling of this config setting to merge_recursive_config() so that other commands can benefit from it as well.

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Original answer (May 2009)

The patch for ignoring eol style has been proposed in June 2007, but it only concerns git diff --ignore-space-at-eol, not git merge.

At the time, the question has been askeed:

Should --ignore-space-at-eol be an option to git-merge ?
Merges are where this functionality matters.
What are the semantics of an auto-resolved merge with those options in effect — are they only used for rename detection, or do we, e.g., not flag conflicts with only whitespace changes ? And if we don’t, which version do we accept automatically ?

Julio C Hamano was not exactly enthusiastic:

This certainly is tempting, but I suspect that should be left to later rounds.
I suspect that it would introduce a concept of two different kinds of diffs, one to be mechanically processed (i.e. use in merge with “git-merge-recursive”, and apply with
“git-am”), and another to be inspected by humans to understand.
It often may be useful to munge the input for the latter case, even though the output from comparing munged input files may not be readily usable for mechanical application.

The general idea, when it comes to git merge, is to rely on the third-party merge tool.

For instance, I have setup DiffMerge to be the tool for Git merge, setting a ruleset which allow that merge tool to ignore eol for certain type of files.

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Setup on Windows, with MSysGit1.6.3, either for DOS or Git bash session, with DiffMerge or KDiff3:

• set a directory into your PATH (here: c:\HOMEWARE\cmd).
• add in that directory the script merge.sh (wrapper for your favorite merge tool)

merge.sh:

#!/bin/sh

# Passing the following parameters to mergetool:
#  local base remote merge_result

alocal=$1
base=$2
remote=$3
result=$4

if [ -f $base ]
then
    #"C:/Program Files/SourceGear/DiffMerge/DiffMerge.exe" "$alocal" "$base" "$remote" -m --result="$result" --title1="Mine" --title2="Merging to: $result" --title3="Theirs"

    # for merge respecting eol, KDiff3 is better than DiffMerge (which will always convert LF into CRLF)
    # KDiff3 will display eol choices (if Windows: CRLF, if Unix LF)
    "C:/Program Files/KDiff3/kdiff3.exe" -m "$base" "$alocal" "$remote" -o "$result"
else
    #there is not always a common ancestor: DiffMerge needing 3 files, BASE will be the result
    #"C:/Program Files/SourceGear/DiffMerge/DiffMerge.exe" "$alocal" "$result" "$remote" -m --result="$result" --title1="Mine" --title2="Merging to: $result" --title3="Theirs"
    
    # KDiff3 however does know how to merge based on 2 files (not just 3)
    "C:/Program Files/KDiff3/kdiff3.exe" -m "$base" "$remote" -o "$result"
fi

• Declare your merge wrapper for Git

Git config commands:

git config --global merge.tool diffmerge
git config --global mergetool.diffmerge.cmd "merge.sh \"$PWD/$LOCAL\" \"$PWD/$BASE\" \"$PWD/$REMOTE\" \"$PWD/$MERGED\"
git config --global mergetool.diffmerge.trustExitCode false
git config --global mergetool.diffmerge.keepBackup false

• Check that autoCRLF is false

git config at system level:

git config ---system core.autoCRLF=false

• Test that, when two lines are identical (but their eol chars), both DiffMerge or KDiff3 will ignore those line during a merge.

DOS script (note: the dos2unix command comes from here, and is used to simulate a Unix eol-style. That command has been copied in the directory mentioned at the beginning of this answer.):

C:\HOMEWARE\git\test>mkdir test_merge
C:\HOMEWARE\git\test>cd test_merge
C:\HOMEWARE\git\test\test_merge>git init
C:\HOMEWARE\git\test\test_merge>echo a1 > a.txt & echo a2 >> a.txt
C:\HOMEWARE\git\test\test_merge>git add a.txt
C:\HOMEWARE\git\test\test_merge>git commit -m "a.txt, windows eol style"
C:\HOMEWARE\git\test\test_merge>git checkout -b windows
Switched to a new branch 'windows'
C:\HOMEWARE\git\test\test_merge>echo a3 >> a.txt & echo a4 >> a.txt
C:\HOMEWARE\git\test\test_merge>git add a.txt
C:\HOMEWARE\git\test\test_merge>git commit -m "add two lines, windows eol style"
C:\HOMEWARE\git\test\test_merge>git checkout master
C:\HOMEWARE\git\test\test_merge>git checkout -b unix
Switched to a new branch 'unix'
C:\HOMEWARE\git\test\test_merge>echo au3 >> a.txt & echo au4 >> a.txt && echo au5 >> a.txt
C:\HOMEWARE\git\test\test_merge>dos2unix a.txt
Dos2Unix: Processing file a.txt ...
C:\HOMEWARE\git\test\test_merge>git add a.txt
C:\HOMEWARE\git\test\test_merge>git commit -m "add 3 lines, all file unix eol style"
[unix c433a63] add 3 lines, all file unix eol style

C:\HOMEWARE\git\test\test_merge>git merge windows
Auto-merging a.txt
CONFLICT (content): Merge conflict in a.txt
Automatic merge failed; fix conflicts and then commit the result.

C:\HOMEWARE\git\test\test_merge>git ls-files -u
100644 39b4c894078a02afb9b1dfeda6f1127c138e38df 1       a.txt
100644 28b3d018872c08b0696764118b76dd3d0b448fca 2       a.txt
100644 3994da66530b4df80189bb198dcfac9b8f2a7b33 3       a.txt

C:\HOMEWARE\git\test\test_merge>git mergetool
Merging the files: a.txt

Normal merge conflict for 'a.txt':
  {local}: modified
  {remote}: modified
Hit return to start merge resolution tool (diffmerge):

At this point (Hitting “return”), DiffMerge or KDiff3 will open, and you will see for yourself what lines are actually merged, and what lines are ignored.

Warning: the result file will always be in Windows eol mode (CRLF) with DiffMerge…
KDiff3 offers to save in one way or another.