tools: add `make format-cpp` to run clang-format on C++ diffs

This patch adds a `make format-cpp` shortcut to the Makefile
that runs clang-format on the C++ diffs, and a
`make format-cpp-build` to install clang-format from
npm.

To format staged changes:

```
$ make format-cpp
```

To format HEAD~1...HEAD (latest commit):

```
$ CLANG_FORMAT_START=`git rev-parse HEAD~1` make format-cpp
```

To format diff between master and current branch head (master...HEAD):

```
$ CLANG_FORMAT_START=master make format-cpp
```

Most of the .clang-format file comes from running

```
$ clang-format --dump-config --style=Google
```

with clang-format built with llvm/trunk 328768 (npm version 1.2.3)

The clang-format version is fixed because different version of
clang-format may format the files differently.

PR-URL: https://github.com/nodejs/node/pull/21997
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Gus Caplan <me@gus.host>
Reviewed-By: Michaël Zasso <targos@protonmail.com>

1 files changed, 27 insertions, 0 deletions

diff --git a/Makefile b/Makefile
index b228cbbf7a0..fc4a094656a 100644
--- a/Makefile
+++ b/Makefile
@@ -1169,6 +1169,33 @@ LINT_CPP_FILES = $(filter-out $(LINT_CPP_EXCLUDE), $(wildcard \
 # and the actual filename is generated so it won't match header guards
 ADDON_DOC_LINT_FLAGS=-whitespace/ending_newline,-build/header_guard
 
+format-cpp-build:
+	cd tools/clang-format && $(call available-node,$(run-npm-install))
+
+format-cpp-clean:
+	$(RM) -r tools/clang-format/node_modules
+
+CLANG_FORMAT_START ?= HEAD
+.PHONY: format-cpp
+# To format staged changes:
+#  $ make format-cpp
+# To format HEAD~1...HEAD (latest commit):
+#  $ CLANG_FORMAT_START=`git rev-parse HEAD~1` make format-cpp
+# To format diff between master and current branch head (master...HEAD):
+#  $ CLANG_FORMAT_START=master make format-cpp
+format-cpp: ## Format C++ diff from $CLANG_FORMAT_START to current changes
+ifneq ("","$(wildcard tools/clang-format/node_modules/)")
+	@echo "Formatting C++ diff from $(CLANG_FORMAT_START).."
+	@$(PYTHON) tools/clang-format/node_modules/.bin/git-clang-format \
+		--binary=tools/clang-format/node_modules/.bin/clang-format \
+		--style=file \
+		$(CLANG_FORMAT_START) -- \
+		$(LINT_CPP_FILES)
+else
+	@echo "clang-format is not installed."
+	@echo "To install (requires internet access) run: $ make format-cpp-build"
+endif
+
 .PHONY: lint-cpp
 # Lints the C++ code with cpplint.py and check-imports.py.
 lint-cpp: tools/.cpplintstamp