pre-commit: installed git hook should have full path to binary (#77638)

pre-commit currently install impure Git hooks that look for the
`pre-commit` binary in PATH. If the user has `pre-commit` loaded via a
nix-shell instead of having it installed then GUI editors, such as
Intellij, won't be able to use Git commit because the hook fails trying
to look for the `pre-commit` binary in PATH.

This patch updates the hook template to use the hardcoded path to the
`pre-commit` binary if it was found, fallback to using the one from
PATH.

pkgs/development/python-modules/pre-commit/default.nix

@@ -7,6 +7,7 @@
 , importlib-metadata
 , importlib-resources
 , nodeenv
+, python
 , six
 , toml
 , virtualenv
@@ -22,6 +23,10 @@ buildPythonApplication rec {
     sha256 = "0l5qg1cw4a0670m96s0ryy5mqz5aslfrrnwpriqgmrnsgdixhj4g";
   };
 
+  patches = [
+    ./hook-tmpl-use-the-hardcoded-path-to-pre-commit.patch
+  ];
+
   propagatedBuildInputs = [
     aspy-yaml
     cached-property
@@ -38,6 +43,11 @@ buildPythonApplication rec {
   # slow and impure
   doCheck = false;
 
+  preFixup = ''
+    substituteInPlace $out/${python.sitePackages}/pre_commit/resources/hook-tmpl \
+      --subst-var-by pre-commit $out
+  '';
+
   meta = with lib; {
     description = "A framework for managing and maintaining multi-language pre-commit hooks";
     homepage = https://pre-commit.com/;

pkgs/development/python-modules/pre-commit/hook-tmpl-use-the-hardcoded-path-to-pre-commit.patch

@@ -0,0 +1,25 @@
+From d9e6999e32112602ec276634cb004eda3ca64ec3 Mon Sep 17 00:00:00 2001
+From: "Wael M. Nasreddine" <wael.nasreddine@gmail.com>
+Date: Mon, 13 Jan 2020 11:04:58 -0800
+Subject: [PATCH] hook-tmpl: use the hardcoded path to pre-commit, if found
+
+---
+ pre_commit/resources/hook-tmpl | 2 ++
+ 1 file changed, 2 insertions(+)
+
+diff --git a/pre_commit/resources/hook-tmpl b/pre_commit/resources/hook-tmpl
+index 213d16e..3a99211 100755
+--- a/pre_commit/resources/hook-tmpl
++++ b/pre_commit/resources/hook-tmpl
+@@ -107,6 +107,8 @@ def _exe() -> Tuple[str, ...]:
+             except OSError:
+                 pass
+ 
++    if os.path.isfile('@pre-commit@/bin/pre-commit') and os.access('@pre-commit@/bin/pre-commit', os.X_OK):
++        return ('@pre-commit@/bin/pre-commit', 'run')
+     if distutils.spawn.find_executable('pre-commit'):
+         return ('pre-commit', 'run')
+ 
+-- 
+2.23.1
+