Documentation for how to create patch files

[chris-martin]

The manual sections The patch phase and Patches ought to describe how to make a .patch file.

All it says right now is

They must be in the format accepted by the $ patch command

and I'm not sure what that means.

[rnhmjoj]

It's a pretty standard unix program: https://en.wikipedia.org/wiki/Patch_%28Unix%29

[vcunat]

We can put this or a similar link to the docs, possibly with a couple examples. The patch program accepts multiple formats, pretty any commonly used patch/diff/...

[chris-martin]

Please, no. A link to Wikipedia never constitutes documentation.

[chris-martin]

Wikipedia says to do this:

diff -u oldFile newFile > mods.diff

So let's try that.

default.nix

{ stdenv }:

stdenv.mkDerivation {
  name = "patch-demo";
  src = ./.;
  patches = [ ./demo.diff ];
}

foo.txt

one
two
three

Let's pretend foo.txt is our source file, and we want demo.diff to be a patch that changes two to four.

chris@cubby ~ ❯❯❯ cd (mktemp -d)
chris@cubby /t/tmp.VMXEEVjRVY ❯❯❯ cp ~/nix/pkgs/patch-demo/foo.txt oldFile
chris@cubby /t/tmp.VMXEEVjRVY ❯❯❯ echo -e "one\nfour\nthree\n" > newFile
chris@cubby /t/tmp.VMXEEVjRVY ❯❯❯ diff -u oldFile newFile > ~/nix/pkgs/patch-demo/demo.diff

So that creates a diff that looks like this:

demo.diff

--- oldFile	2017-11-17 15:19:40.014637150 -0500
+++ newFile	2017-11-17 15:20:09.628909087 -0500
@@ -1,3 +1,4 @@
 one
-two
+four
 three
+

So far so good, I made a patch file! But it looks like I did something wrong, because most of the patches in nixpkgs have a header that looks something like this

From 33b25c2e3c7a002c7f726cd79fc4bab22b1299be Mon Sep 17 00:00:00 2001
From: Thomas Tuegel <ttuegel@gmail.com>
Date: Tue, 27 Oct 2015 18:07:54 -0500
Subject: [PATCH] follow symlinks

---
 src/appearancegtk2.cpp  | 2 +-
 src/iconthemesmodel.cpp | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

Mine doesn't and I don't know why it's different.

I'm not sure how it will know which file to apply the patch to. Indeed it doesn't work:

chris@cubby ~ ❯❯❯ nix install patch-demo
installing ‘patch-demo’
these derivations will be built:
  /nix/store/5jvgpr4bq6ji04nxd4imgbsg2jv5di4q-patch-demo.drv
building path(s) ‘/nix/store/vrda5am5jl91bx8qmm8cg2g2j7s3662g-patch-demo’
unpacking sources
unpacking source archive /nix/store/1h5cgxhpban3bw4fsb2mr7flxr1zwa8w-patch-demo
source root is patch-demo
patching sources
applying patch /nix/store/3mgg0p8irr7z0g3ijwfr3l38kj3lb7da-demo.diff
can't find file to patch at input line 3
Perhaps you used the wrong -p or --strip option?
The text leading up to this was:
--------------------------
|--- oldFile    2017-11-17 15:19:40.014637150 -0500
|+++ newFile    2017-11-17 15:20:09.628909087 -0500
--------------------------
File to patch:
Skip this patch? [y]
Skipping patch.
1 out of 1 hunk ignored
builder for ‘/nix/store/5jvgpr4bq6ji04nxd4imgbsg2jv5di4q-patch-demo.drv’ failed with exit code 1

So I guess I need to edit the diff file to fix the file name?

demo.diff

--- foo.txt	2017-11-17 15:19:40.014637150 -0500
+++ foo.txt	2017-11-17 15:20:09.628909087 -0500
@@ -1,3 +1,4 @@
 one
-two
+four
 three
+

chris@cubby ~ ❯❯❯ nix install patch-demo
installing ‘patch-demo’
these derivations will be built:
  /nix/store/i5ikqs1smf01lywr7jpi2q8s47zv9kcx-patch-demo.drv
building path(s) ‘/nix/store/rw1hi6qvnsmbaayxk12kfcrcmf2lr0fc-patch-demo’
unpacking sources
unpacking source archive /nix/store/ivynk2f4gwvnn503vqrcxn7xhp47cvfn-patch-demo
source root is patch-demo
patching sources
applying patch /nix/store/b6pfb9mh2yacj1dqz26g7qy6qfhp0pz1-demo.diff
can't find file to patch at input line 3
Perhaps you used the wrong -p or --strip option?
The text leading up to this was:
--------------------------
|--- foo.txt    2017-11-17 15:19:40.014637150 -0500
|+++ foo.txt    2017-11-17 15:20:09.628909087 -0500
--------------------------
File to patch: 
Skip this patch? [y] 
Skipping patch.
1 out of 1 hunk ignored
builder for ‘/nix/store/i5ikqs1smf01lywr7jpi2q8s47zv9kcx-patch-demo.drv’ failed with exit code 1
error: build of ‘/nix/store/i5ikqs1smf01lywr7jpi2q8s47zv9kcx-patch-demo.drv’ failed

Nope, still doesn't work. Not sure why.

[orivej]

The patch header is optional. The problem with your patch is that by default file names are expected to be prefixed with one arbitrary directory, e.g. a/foo.txt, not just foo.txt.

I'd recommend this method of generating patches:

cd some-dir/with/files
git init
git add . # or "git add some-file" if there is a lot of files and directories here
edit some files
git diff > ../changes.patch

[chris-martin]

@orivej Thank you!

I submitted #31778 to add that to the manual.

[eyJhb]

I know this is a long time since, but there must be a better and easier way by now.
Making a patch for Firefox, and the initial git add ., takes some time as one might imagine.

[rnhmjoj]

The firefox codebase is what, mercurial? I would suggest that instead. Or just making a copy before modifying the file and using diff -u a b.

[orivej]

You can git add path1 path2 … — only paths that you want to change.

[nixos-discourse]

This issue has been mentioned on NixOS Discourse. There might be relevant details there:

https://discourse.nixos.org/t/how-to-deal-with-pip-install-in-makefile/22531/5