[PATCH 3 of 3] diff: add a fast path to avoid loading binary contents

[Yuya Nishihara]

On Thu, 4 May 2017 00:00:15 -0700, Jun Wu wrote:
> # HG changeset patch
> # User Jun Wu <quark at fb.com>
> # Date 1493880641 25200
> #      Wed May 03 23:50:41 2017 -0700
> # Node ID d3b641866aa3ee2ff36a62b6e05f9e8849ef1ae6
> # Parent  12370108647046bd6ec1af8365ee908746a135f3
> # Available At https://bitbucket.org/quark-zju/hg-draft
> #              hg pull https://bitbucket.org/quark-zju/hg-draft -r d3b641866aa3
> diff: add a fast path to avoid loading binary contents
> 
> When diffing binary contents, with certain configs, we can show
> "Binary file <name> has changed" without actual content.
> 
> That allows a fast path where we could avoid providing actual binary
> contents. Note: in that case we still need to test if two contents are the
> same, that's done by using "filectx.cmp", which could have its own fast
> path.
> 
> diff --git a/mercurial/patch.py b/mercurial/patch.py
> --- a/mercurial/patch.py
> +++ b/mercurial/patch.py
> @@ -2533,10 +2533,8 @@ def trydiff(repo, revs, ctx1, ctx2, modi
>          if f1:
>              fctx1 = getfilectx(f1, ctx1)
> -            content1 = fctx1.data()
>              if opts.git or losedatafn:
>                  flag1 = ctx1.flags(f1)
>          if f2:
>              fctx2 = getfilectx(f2, ctx2)
> -            content2 = fctx2.data()
>              if opts.git or losedatafn:
>                  flag2 = ctx2.flags(f2)
> @@ -2585,4 +2583,22 @@ def trydiff(repo, revs, ctx1, ctx2, modi
>              header.append(diffline(path1, revs))
>  
> +        if binary and not opts.text and (opts.nobinary or not opts.git):

Real contents are necessary if 'opts.git and opts.index > 0' (even if
opts.nobinary.)

> +            # fast path: no binary content will be displayed, content1 and
> +            # content2 are only used for equivalent test. cmp() could have a
> +            # fast path.
> +            if fctx1 is not None:
> +                content1 = b'\0'
> +            if fctx2 is not None:
> +                if fctx1 is not None and not fctx1.cmp(fctx2):
> +                    content2 = b'\0' # not different
> +                else:
> +                    content2 = b'\0\0'
> +        else:
> +            # normal path: load contents
> +            if fctx1 is not None:
> +                content1 = fctx1.data()
> +            if fctx2 is not None:
> +                content2 = fctx2.data()
> +
>          if binary and opts.git and not opts.nobinary and not opts.text:
>              text = mdiff.b85diff(content1, content2)