Re: What's the idea of specifying binary=true together with textconv?

On Wed, Sep 27, 2017 at 10:06:25PM +0300, Ilya Kantor wrote:

When textconv is specified, the program is always used for conversion.

Not always. It's enabled by default for the git-diff and git-log"
porcelain, but not for plumbing commands, nor for git-format-patch
(which needs to create a patch that can be applied). And it can be
disabled with --no-textconv.

E.g. consider this:
[diff "png"]
  textconv = wc

Even if a png file is ASCII (manually created), wc gets called, and
the result is made of its output.

So, the question is: why should one specify binary = true together
with textconv?

There is an example in docs:
[diff "ps"]
  textconv = ps2ascii
  binary = true

...But what binary = true does here?
Even if we remove it, textconv is called for all ps-files.

Setting binary=true overrides Git's binary-detection heuristics. When
textconv is in effect, those heuristics aren't used at all. But when
it's disabled, if you want to make sure a file is marked as binary, it
would kick in then. For example:

  $ git init
  $ echo fake-binary >foo.png
  $ echo "*.png diff=png" >.git/info/attributes
  $ git config diff.png.textconv "sed s/^/converted:/"
  $ git add .
  $ git commit -m foo

  $ git show
  ...
  --- /dev/null
  +++ b/foo.png
  @@ -0,0 +1 @@
  +converted:fake-binary

  $ git format-patch --stdout -1
  ...
  --- /dev/null
  +++ b/foo.png
  @@ -0,0 +1 @@
  +fake-binary

  $ git config diff.png.binary true
  $ git format-patch --stdout -1
  diff --git a/foo.png b/foo.png
  new file mode 100644
  index 0000000000000000000000000000000000000000..96060daf0866dbaf9538b76587f0da801bed4a5f
  GIT binary patch
  literal 12
  TcmYdG%udx!%FIhFs^kIy9YO?D
  
  literal 0
  HcmV?d00001

It's a pretty rare corner case where this is useful. After all, if your
file really isn't binary, then a text patch is actually preferable. But
you could imagine cases where the heuristics are wrong (e.g., a single
NUL very far into the file).

-Peff