[pitivi] Update the git hook to support GNOME Builder

[Alexandru Băluț <alexbalut src gnome org>]

commit 3ddc6ed6ccf372c71e2ad89a656746593da4d5e1
Author: Alexandru Băluț <alexandru balut gmail com>
Date:   Sun Dec 29 22:22:53 2019 +0100

    Update the git hook to support GNOME Builder

 docs/HACKING.md | 28 +++++++++++++++++++++++++---
 pre-commit.hook | 43 ++++++++++++++++++++++++++++++-------------
 2 files changed, 55 insertions(+), 16 deletions(-)
---
diff --git a/docs/HACKING.md b/docs/HACKING.md
index 355b7175..c258d08f 100644
--- a/docs/HACKING.md
+++ b/docs/HACKING.md
@@ -4,21 +4,43 @@ short-description: Using the Pitivi development environment
 
 # Hacking on Pitivi
 
+There are two ways to set up a flatpak sandbox with all the
+dependencies required to run and develop Pitivi. We recommend
+the advanced way, but if you want something quick, go ahead with
+the easy way.
+
 ## The easy way
 
 The easy way to setup the development environment is to follow the
 [GNOME Newcomers guide](https://wiki.gnome.org/Newcomers/).
 
-Make sure to use the right git repository:
+This implies using GNOME Builder to manage the dependencies sandbox.
+
+Clone the `https://gitlab.gnome.org/GNOME/pitivi.git` git repository
+in GNOME Builder.
+
+To run the unittests, click in Builder: Unittests > pitivi > Pitivi unit tests.
+Make sure they all pass, or tell us about any failures.
+
+To be able to use our pre-commit git hook, run:
+
+```
+$ cd ~/Projects/pitivi
+$ ln -s ../../pre-commit.hook .git/hooks/pre-commit
+```
 
->   **https://gitlab.gnome.org/GNOME/pitivi.git**
+When creating commits, for the pre-commit git hook to work properly
+it has to run in the sandbox. This is possible only by running `git`
+in a Build Terminal in GNOME Builder. You might want to
+`export EDITOR=nano` if you get "error: unable to start editor 'vi'"
+when you have to enter a commit message.
 
 
 ## Setting up the advanced development environment
 
> NOTE: This way of setting the development environment is sensibly more complex
> but also more flexible than the one for newcomers. If you are a  beginner
-> or if you usually use [gnome-builder](https://wiki.gnome.org/Apps/Builder)
+> or if you usually use [GNOME Builder](https://wiki.gnome.org/Apps/Builder)
> as your main IDE, follow, as previously advised, the
> [GNOME Newcomers guide](https://wiki.gnome.org/Newcomers/)
 
diff --git a/pre-commit.hook b/pre-commit.hook
index 71da257d..5def5e7c 100755
--- a/pre-commit.hook
+++ b/pre-commit.hook
@@ -1,20 +1,37 @@
 #!/usr/bin/env bash
 
 # This is symlinked from .git/hooks/pre-commit when entering
-# the dev env with `source bin/pitivi-env`.
-
-if [ -z "${PITIVI_REPO_DIR}" ]; then
-    echo "ERROR: You're not in the Pitivi development environment."
-    echo
-    echo "       Enter the development environment by running:"
-    echo "           $ . bin/pitivi/env"
-    echo
-    echo "       See http://developer.pitivi.org/HACKING.html for details."
-    echo
-    exit 1
-fi
+# the dev env with `. bin/pitivi-env`, or manually.
 
 TOPLEVEL=$(git rev-parse --show-toplevel)
 export PYTHONPATH=$TOPLEVEL/pitivi/coptimizations/.libs:$PYTHONPATH
 
-$TOPLEVEL/build/flatpak/pitivi-flatpak pre-commit run --config .pre-commit-config.yaml || exit 1
+PRECOMMIT=""
+if test -n "${PITIVI_REPO_DIR}"
+then
+    PRECOMMIT="$TOPLEVEL/build/flatpak/pitivi-flatpak pre-commit"
+elif test -n "${INSIDE_GNOME_BUILDER}"
+then
+    PRECOMMIT=$(which /app/bin/pre-commit)
+fi
+
+if test -z "$PRECOMMIT"
+then
+    cat <<EOF
+ERROR: Cannot find the flatpak sandbox.
+
+       If you are using GNOME Builder, you can commit only
+       from a Build Terminal.
+
+       If you are using the Pitivi development environment,
+       enter it by running:
+           $ . bin/pitivi-env
+
+       See http://developer.pitivi.org/HACKING.html for details.
+
+EOF
+    exit 1
+fi
+
+
+$PRECOMMIT run --config .pre-commit-config.yaml || exit 1