Add option to scripts-dev/lint.sh to only lint files changed since the last git commit

CONTRIBUTING.md

@@ -63,6 +63,10 @@ run-time:
 ./scripts-dev/lint.sh path/to/file1.py path/to/file2.py path/to/folder
 ```
 
+You can also provided the `-d` option, which will lint the files that have been
+changed since the last git commit. This will often be significantly faster than
+linting the whole codebase.
+
 Before pushing new changes, ensure they don't produce linting errors. Commit any
 files that were corrected.
 

changelog.d/8472.feature

@@ -0,0 +1 @@
+Add `-d` option to `./scripts-dev/lint.sh` to lint files that have changed since the last git commit.

scripts-dev/lint.sh

@@ -1,4 +1,4 @@
-#!/bin/sh
+#!/bin/bash
 #
 # Runs linting scripts over the local Synapse checkout
 # isort - sorts import statements
@@ -7,15 +7,79 @@
 
 set -e
 
-if [ $# -ge 1 ]
-then
-  files=$*
-else
-  files="synapse tests scripts-dev scripts contrib synctl"
+usage() {
+  echo
+  echo "Usage: $0 [-h] [-d] [paths...]"
+  echo
+  echo "-d"
+  echo "  Lint files that have changed since the last git commit."
+  echo
+  echo "  If paths are provided and this option is set, both provided paths and those"
+  echo "  that have changed since the last commit will be linted."
+  echo
+  echo "  If no paths are provided and this option is not set, all files will be linted."
+  echo
+  echo "  Note that paths will be excluded if they both have a file extension, and it is not 'py'."
+  echo "-h"
+  echo "  Display this help text."
+}
+
+USING_DIFF=0
+files=()
+
+while getopts ":dh" opt; do
+  case $opt in
+    d)
+      USING_DIFF=1
+
+      # Check both staged and non-staged changes
+      for path in $(git diff HEAD --name-only); do
+        filename=$(basename "$path")
+        file_extension="${filename##*.}"
+
+        # If an extension is present, and it's something other than 'py',
+        # then ignore this file
+        if [[ -n ${file_extension+x} && $file_extension != "py" ]]; then
+          continue
+        fi
+
+        # Append this path to our list of files to lint
+        files+=("$path")
+      done
+      ;;
+    h)
+      usage
+      exit
+      ;;
+    \?)
+      echo "ERROR: Invalid option: -$OPTARG" >&2
+      usage
+      exit
+      ;;
+  esac
+done
+
+# Strip any options from the command line arguments now that
+# we've finished processing them
+shift "$((OPTIND-1))"
+
+# Append any remaining arguments as files to lint
+files+=("$@")
+
+# If we were not asked to lint changed files, and no paths were found as a result,
+# then lint everything!
+if [[ $USING_DIFF -eq 0 && -z ${files+x} ]]; then
+  # Lint all source code files and directories
+  files=("synapse" "tests" "scripts-dev" "scripts" "contrib" "synctl")
 fi
 
-echo "Linting these locations: $files"
-isort $files
-python3 -m black $files
+echo "Linting these paths: ${files[*]}"
+echo
+
+# Print out the commands being run
+set -x
+
+isort "${files[@]}"
+python3 -m black "${files[@]}"
 ./scripts-dev/config-lint.sh
-flake8 $files
+flake8 "${files[@]}"