Re: Don't complain about changed file when it hasn't changed

[Davis Herring]

> I don't understand why Git touches files it doesn't need to change.
> It can (and does, AFAIK) compute the checksum of a file to know
> whether it changed.

True that for a basic "git checkout new-branch" Git compares the (tree 
and blob) hashes to decide what files to touch.  However:

$ git init
Initialized empty Git repository in /tmp/grd/.git/
$ touch a b
$ git add a b
$ git commit -m "initial"
[master (root-commit) ad16e59] initial
 0 files changed, 0 insertions(+), 0 deletions(-)
 create mode 100644 a
 create mode 100644 b
$ echo >>a
$ git commit -am "newline: a"
[master 9023233] newline: a
 1 files changed, 1 insertions(+), 0 deletions(-)
$ echo >>a
$ git commit -am "newline 2: a"
[master eeb78ed] newline 2: a
 1 files changed, 1 insertions(+), 0 deletions(-)
$ git checkout -q HEAD^
$ echo >>b
$ git commit -am "newline: b"
[detached HEAD 2332479] newline: b
 1 files changed, 1 insertions(+), 0 deletions(-)
$ stat -c %y b
2016-08-29 13:15:46.820780908 -0600
$ git rebase master
First, rewinding head to replay your work on top of it...
Applying: newline: b
$ stat -c %y b
2016-08-29 13:16:04.538756145 -0600

As the output says, it "rewinds" your changes and reapplies them on top 
of the chosen commit.  This could be considered an artifact of "git 
rebase"'s implementation as a shell script on top of the other git 
commands, but given the possibility of merge conflicts to resolve it's 
not clear that it "ought" to be done entirely in-memory before updating 
only those files that need it on disk.

> AFAIU, the undo records are kept because you don't revert the buffer,
> not because of the check.  You could refuse to revert with the current
> code, and keep the undo information, right?

You could, but Emacs would be trusting you that the file really wasn't 
altered.  You could check yourself with `diff-buffer-with-file', but 
that's tedious; I find I usually just toss the undo information (by 
typing 'r' in response to the query).

Davis

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