[makefile] 10x speed up checking/fixing (#7403)

* [makefile] check/fix only modified since branching files

* fix phonies

* parametrize dirs

* have only one source for dirs to check

* look ma, no autoformatters here

Makefile

-.PHONY: quality_checks quality style fixup test test-examples docs
+.PHONY: modified_only_fixup extra_quality_checks quality style fixup fix-copies test test-examples docs
+
+
+check_dirs := examples templates tests src utils
+
+# get modified files since the branch was made
+fork_point_sha := $(shell git merge-base --fork-point master)
+joined_dirs    := $(shell echo $(check_dirs) | tr " " "|")
+modified_files := $(shell git diff --name-only $(fork_point_sha) | egrep '^($(joined_dirs))')
+#$(info modified files are: $(modified_files))
+
+modified_only_fixup:
+	@if [ -n "$(modified_files)" ]; then \
+		echo "Checking/fixing $(modified_files)"; \
+		black $(modified_files); \
+		isort $(modified_files); \
+		flake8 $(modified_files); \
+	else \
+		echo "No relevant files were modified"; \
+	fi
 
 # Check that source code meets quality standards
 
-quality_checks:
-	flake8 examples templates tests src utils
+extra_quality_checks:
 	python utils/check_copies.py
 	python utils/check_repo.py
 
+# this target runs checks on all files
 quality:
-	black --check examples templates tests src utils
-	isort --check-only examples templates tests src utils
-	${MAKE} quality_checks
+	black --check $(check_dirs)
+	isort --check-only $(check_dirs)
+	flake8 $(check_dirs)
+	${MAKE} extra_quality_checks
 
 # Format source code automatically and check is there are any problems left that need manual fixing
 
 style:
-	black examples templates tests src utils
-	isort examples templates tests src utils
+	black $(check_dirs)
+	isort $(check_dirs)
+
+# Super fast fix and check target that only works on relevant modified files since the branch was made
 
-fixup: style quality_checks
+fixup: modified_only_fixup extra_quality_checks
 
 # Make marked copies of snippets of codes conform to the original