Travis: Add static check for Python black formatting

Also install and use pygmentize to visualize clang-format and black
diffs.

.travis.yml

@@ -129,9 +129,6 @@ matrix:
 
 before_install:
   - eval "${MATRIX_EVAL}"
-  - if [ "$STATIC_CHECKS" = "yes" ]; then
-      unset SCONS_CACHE;
-    fi
 
 install:
   - if [ "$TRAVIS_OS_NAME" = "linux" ]; then
@@ -150,6 +147,10 @@ install:
       ./emsdk/emsdk install latest;
       ./emsdk/emsdk activate latest;
     fi
+  - if [ "$STATIC_CHECKS" = "yes" ]; then
+      unset SCONS_CACHE;
+      pip3 install --user black pygments;
+    fi
 
 before_script:
   - if [ "$PLATFORM" = "android" ]; then
@@ -160,6 +161,7 @@ before_script:
 script:
   - if [ "$STATIC_CHECKS" = "yes" ]; then
       sh ./misc/travis/clang-format.sh &&
+      sh ./misc/travis/black-format.sh &&
       doc/tools/makerst.py --dry-run doc/classes modules;
     else
       scons -j2 CC=$CC CXX=$CXX platform=$PLATFORM tools=$TOOLS target=$TARGET $OPTIONS $EXTRA_ARGS &&

misc/travis/black-format.sh

@@ -0,0 +1,48 @@
+#!/bin/sh
+
+BLACK=black
+BLACK_OPTIONS="-l 120"
+
+if [ "$TRAVIS_PULL_REQUEST" != "false" ]; then
+    # Travis only clones the PR branch and uses its HEAD commit as detached HEAD,
+    # so it's problematic when we want an exact commit range for format checks.
+    # We fetch upstream to ensure that we have the proper references to resolve.
+    # Ideally we would use $TRAVIS_COMMIT_RANGE but it doesn't play well with PR
+    # updates, as it only includes changes since the previous state of the PR.
+    if [ -z "$(git remote | grep upstream)" ]; then
+      git remote add upstream https://github.com/godotengine/godot \
+          --no-tags -f -t $TRAVIS_BRANCH
+    fi
+    RANGE="upstream/$TRAVIS_BRANCH HEAD"
+else
+    # Test only the last commit, since $TRAVIS_COMMIT_RANGE wouldn't support
+    # force pushes.
+    RANGE=HEAD
+fi
+
+FILES=$(git diff-tree --no-commit-id --name-only -r $RANGE | grep -v thirdparty/| grep -E "(SConstruct|SCsub|\.py)$")
+echo "Checking files:\n$FILES"
+
+# create a random filename to store our generated patch
+prefix="static-check-black"
+suffix="$(date +%s)"
+patch="/tmp/$prefix-$suffix.patch"
+
+for file in $FILES; do
+    "$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 formatting rules.\n"
+    rm -f "$patch"
+    exit 0
+fi
+
+# a patch has been created, notify the user and exit
+printf "\n*** The following differences were found between the code to commit "
+printf "and the black formatting rules:\n\n"
+pygmentize -l diff "$patch"
+printf "\n*** Aborting, please fix your commit(s) with 'git commit --amend' or 'git rebase -i <hash>'\n"
+exit 1

misc/travis/clang-format.sh

@@ -8,8 +8,10 @@ if [ "$TRAVIS_PULL_REQUEST" != "false" ]; then
     # We fetch upstream to ensure that we have the proper references to resolve.
     # Ideally we would use $TRAVIS_COMMIT_RANGE but it doesn't play well with PR
     # updates, as it only includes changes since the previous state of the PR.
-    git remote add upstream https://github.com/godotengine/godot \
+    if [ -z "$(git remote | grep upstream)" ]; then
-        --no-tags -f -t $TRAVIS_BRANCH
+      git remote add upstream https://github.com/godotengine/godot \
+          --no-tags -f -t $TRAVIS_BRANCH
+    fi
     RANGE="upstream/$TRAVIS_BRANCH HEAD"
 else
     # Test only the last commit, since $TRAVIS_COMMIT_RANGE wouldn't support
@@ -41,6 +43,6 @@ fi
 # a patch has been created, notify the user and exit
 printf "\n*** The following differences were found between the code to commit "
 printf "and the clang-format rules:\n\n"
-cat "$patch"
+pygmentize -l diff "$patch"
 printf "\n*** Aborting, please fix your commit(s) with 'git commit --amend' or 'git rebase -i <hash>'\n"
 exit 1