Hooks: Add pre-commit hook for psf/black formatting

4 files changed, 146 insertions, 16 deletions

diff --git a/misc/hooks/README.md b/misc/hooks/README.md
index b18ba7df38..dad5300a09 100644
--- a/misc/hooks/README.md
+++ b/misc/hooks/README.md
@@ -5,16 +5,22 @@ contributors to make sure they comply with our requirements.
 
 ## List of hooks
 
-- Pre-commit hook for clang-format: Applies clang-format to the staged files
-  before accepting a commit; blocks the commit and generates a patch if the
-  style is not respected.
-  Should work on Linux and macOS. You may need to edit the file if your
-  clang-format binary is not in the `$PATH`, or if you want to enable colored
-  output with pygmentize.
-- Pre-commit hook for makerst: Checks the class reference syntax using `makerst.py`.
-  Should work on Linux and macOS.
+- Pre-commit hook for `clang-format`: Applies `clang-format` to the staged
+  files before accepting a commit; blocks the commit and generates a patch if
+  the style is not respected.
+  You may need to edit the file if your `clang-format` binary is not in the
+  `PATH`, or if you want to enable colored output with `pygmentize`.
+- Pre-commit hook for `black`: Applies `black` to the staged Python files
+  before accepting a commit.
+- Pre-commit hook for `makerst`: Checks the class reference syntax using
+  `makerst.py`.
 
 ## Installation
 
-Copy all the files from this folder into your `.git/hooks` folder, and make sure
-the hooks and helper scripts are executable.
+Copy all the files from this folder into your `.git/hooks` folder, and make
+sure the hooks and helper scripts are executable.
+
+The hooks rely on bash scripts and tools which should be in the system `PATH`,
+so they should work out of the box on Linux/macOS, and might work on Windows
+when using `git-bash.exe` with `clang-format`, Python, `black`, etc. in the
+`PATH`.
diff --git a/misc/hooks/pre-commit b/misc/hooks/pre-commit
index 36e9935785..40cb00253b 100755
--- a/misc/hooks/pre-commit
+++ b/misc/hooks/pre-commit
@@ -14,7 +14,7 @@
 # as this script. Hooks should return 0 if successful and nonzero to cancel the
 # commit. They are executed in the order in which they are listed.
 #HOOKS="pre-commit-compile pre-commit-uncrustify"
-HOOKS="pre-commit-clang-format pre-commit-makerst"
+HOOKS="pre-commit-clang-format pre-commit-black pre-commit-makerst"
 ###########################################################
 # There should be no need to change anything below this line.
 
diff --git a/misc/hooks/pre-commit-black b/misc/hooks/pre-commit-black
new file mode 100755
index 0000000000..3dd0a13330
--- /dev/null
+++ b/misc/hooks/pre-commit-black
@@ -0,0 +1,128 @@
+#!/usr/bin/env bash
+
+# git pre-commit hook that runs a black stylecheck.
+# Based on pre-commit-clang-format.
+
+##################################################################
+# SETTINGS
+# Set path to black binary.
+BLACK=`which black`
+BLACK_OPTIONS="-l 120"
+
+# Remove any older patches from previous commits. Set to true or false.
+DELETE_OLD_PATCHES=false
+
+# File types to parse.
+FILE_NAMES="SConstruct SCsub"
+FILE_EXTS="py"
+
+# Use pygmentize instead of cat to parse diff with highlighting.
+# Install it with `pip install pygments` (Linux) or `easy_install Pygments` (Mac)
+# READER="pygmentize -l diff"
+READER=cat
+
+##################################################################
+# There should be no need to change anything below this line.
+
+. "$(dirname -- "$0")/canonicalize_filename.sh"
+
+# exit on error
+set -e
+
+# check whether the given file matches any of the set extensions
+matches_name_or_extension() {
+    local filename=$(basename "$1")
+    local extension=".${filename##*.}"
+
+    for name in $FILE_NAMES; do [[ "$name" == "$filename" ]] && return 0; done
+    for ext in $FILE_EXTS; do [[ "$ext" == "$extension" ]] && return 0; done
+
+    return 1
+}
+
+# necessary check for initial commit
+if git rev-parse --verify HEAD >/dev/null 2>&1 ; then
+    against=HEAD
+else
+    # Initial commit: diff against an empty tree object
+    against=4b825dc642cb6eb9a060e54bf8d69288fbee4904
+fi
+
+if [ ! -x "$BLACK" ] ; then
+    printf "Error: black executable not found.\n"
+    printf "Set the correct path in $(canonicalize_filename "$0").\n"
+    exit 1
+fi
+
+# create a random filename to store our generated patch
+prefix="pre-commit-black"
+suffix="$(date +%s)"
+patch="/tmp/$prefix-$suffix.patch"
+
+# clean up any older black patches
+$DELETE_OLD_PATCHES && rm -f /tmp/$prefix*.patch
+
+# create one patch containing all changes to the files
+git diff-index --cached --diff-filter=ACMR --name-only $against -- | while read file;
+do
+    # ignore thirdparty files
+    if grep -q "thirdparty" <<< $file; then
+        continue;
+    fi
+
+    # ignore file if not one of the names or extensions we handle
+    if ! matches_name_or_extension "$file"; then
+        continue;
+    fi
+
+    # format our file with black, create a patch with diff and append it to our $patch
+    # The sed call is necessary to transform the patch from
+    #    --- $file timestamp
+    #    +++ $file timestamp
+    # to both lines working on the same file and having a/ and b/ prefix.
+    # Else it can not be applied with 'git apply'.
+    "$BLACK" "$BLACK_OPTIONS" --diff "$file" | \
+        sed -e "1s|--- |--- a/|" -e "2s|+++ |+++ b/|" >> "$patch"
+done
+
+# if no patch has been generated all is ok, clean up the file stub and exit
+if [ ! -s "$patch" ] ; then
+    printf "Files in this commit comply with the black formatter rules.\n"
+    rm -f "$patch"
+    exit 0
+fi
+
+# a patch has been created, notify the user and exit
+printf "\nThe following differences were found between the code to commit "
+printf "and the black formatter rules:\n\n"
+$READER "$patch"
+printf "\n"
+
+# Allows us to read user input below, assigns stdin to keyboard
+exec < /dev/tty
+
+while true; do
+    read -p "Do you want to apply that patch (Y - Apply, N - Do not apply, S - Apply and stage files)? [Y/N/S] " yn
+    case $yn in
+        [Yy] ) git apply $patch;
+        printf "The patch was applied. You can now stage the changes and commit again.\n\n";
+        break
+        ;;
+        [Nn] ) printf "\nYou can apply these changes with:\n  git apply $patch\n";
+        printf "(may need to be called from the root directory of your repository)\n";
+        printf "Aborting commit. Apply changes and commit again or skip checking with";
+        printf " --no-verify (not recommended).\n\n";
+        break
+        ;;
+        [Ss] ) git apply $patch;
+        git diff-index --cached --diff-filter=ACMR --name-only $against -- | while read file;
+        do git add $file;
+        done
+        printf "The patch was applied and the changed files staged. You can now commit.\n\n";
+        break
+        ;;
+        * ) echo "Please answer yes or no."
+        ;;
+    esac
+done
+exit 1 # we don't commit in any case
diff --git a/misc/hooks/pre-commit-clang-format b/misc/hooks/pre-commit-clang-format
index e309233a8b..f3689890df 100755
--- a/misc/hooks/pre-commit-clang-format
+++ b/misc/hooks/pre-commit-clang-format
@@ -15,22 +15,18 @@
 
 ##################################################################
 # SETTINGS
-# Set path to clang-format binary
-# CLANG_FORMAT="/usr/bin/clang-format"
+# Set path to clang-format binary.
 CLANG_FORMAT=`which clang-format`
 
 # Remove any older patches from previous commits. Set to true or false.
-# DELETE_OLD_PATCHES=false
 DELETE_OLD_PATCHES=false
 
 # Only parse files with the extensions in FILE_EXTS. Set to true or false.
 # If false every changed file in the commit will be parsed with clang-format.
 # If true only files matching one of the extensions are parsed with clang-format.
-# PARSE_EXTS=true
 PARSE_EXTS=true
 
 # File types to parse. Only effective when PARSE_EXTS is true.
-# FILE_EXTS=".c .h .cpp .hpp"
 FILE_EXTS=".c .h .cpp .hpp .cc .hh .cxx .m .mm .inc .java .glsl"
 
 # Use pygmentize instead of cat to parse diff with highlighting.