(Some?) control codes not escaped when using `git add -p`

Hello list,

Running git 2.7.4, I’ve run into an issue where control codes that would normally be escaped when using `git diff` are not similarly escaped when using `git add -p`.

As a concrete example, I have a text file including the following "text":

:map ^[[H <Home> :map ^[[5~ ^B "page up :map ^[[6~ ^F "page down

Except each ^x above is the literal ctrl+x (i.e. ctrl+v followed by ctrl+x). These are not lines that have been added or removed from the document, they're just context lines.

Using `git diff`, these special characters are elided from the diff output (though the latter two lines cause special coloring in the diff output so perhaps they're not being entirely escaped?), but when using `git add -p` upon reaching the chunk in question my terminal interprets a literal "page up" input and corrupts the output.

Here's a screenshot of what I see when I use `git diff`: https://i.imgur.com/FOXWEIi.png

And here's what I see when use `git add -p`: https://i.imgur.com/i5hqhFX.png

As you can see, in the second example the cursor is a few lines from the top of the screen, as the text output started midway down and then jumped to the start and continued from there on encountering the literal 'Page Up' sequence in the diff'd text.

I'm not sure _what_ the correct approach would be here (does git faithfully print whatever it finds in the file or does it attempt to escape it instead?) but it seems to me that the lack of consistency between the two commands is a bug as whichever approach is taken, a context line in `git diff` should surely be output to the terminal in the same way as a context line in `git add -p`?

The obvious solution is to embrace isatty(2) religiously, but I'm not sure how the everyone else feels about that (or if it's already used elsewhere).

Anyway, I'm sure I'm not the only one to run into this. Seeking options and interested in the various viewpoints on how this should be correctly handled (or explanations for why it's already correct as-is).

Cheers,

Mahmoud Al-Qudsi NeoSmart Technologies

On Thu, Oct 12, 2017 at 12:59:06PM -0500, Mahmoud Al-Qudsi wrote:

The diffs generated for "git diff" and "git add -p" are done by the exact same code. And that code doesn't do any escaping or cleverness; it will output the raw bytes of the difference.

What is likely causing the different in what you see is that "git diff". outputs through a pager, and the snippets of "add -p" do not. The default pager, "less", does escape some control codes (but with the -R option, which git uses by default, it passes through colors).

Try:

  git --no-pager diff

or:

  GIT_PAGER=cat git diff

and you'll likely see output similar to what you get with "add -p".

The reason that "add -p" doesn't go through a pager by default is simply that it would be annoying, since we show snippets and then ask for user input.

However, since Git v2.9.0, "add -p" (and all of the interactive commands like "checkout -p", etc) know about the interactive.diffFilter config option. You could use that to munge the results however you like. E.g.:

  # we can't use [:cntrl:] here because we want to keep newlines.
  # likewise, we want to keep ESC for color codes
  git config interactive.diffFilter "tr '\000-\011\013-\032\034-\037' '?'"

-Peff