From 83fc988bec374d6beb197e6dde9aef20b6f52b8d Mon Sep 17 00:00:00 2001
From: Andrea Bedini <andrea@andreabedini.com>
Date: Mon, 18 Mar 2024 23:57:15 +0800
Subject: [PATCH] Create compile-commands.json with Make

---
 .gitignore                 |  1 +
 mk/compilation-database.mk | 11 +++++++++++
 mk/lib.mk                  |  8 ++++++++
 mk/patterns.mk             | 36 +++++++++++++++++++++++++++++++++---
 mk/tracing.mk              |  2 ++
 5 files changed, 55 insertions(+), 3 deletions(-)
 create mode 100644 mk/compilation-database.mk

diff --git a/.gitignore b/.gitignore
index 7bf77adf4..01fafa5a9 100644
--- a/.gitignore
+++ b/.gitignore
@@ -142,6 +142,7 @@ GTAGS
 
 # auto-generated compilation database
 compile_commands.json
+*.compile_commands.json
 
 nix-rust/target
 
diff --git a/mk/compilation-database.mk b/mk/compilation-database.mk
new file mode 100644
index 000000000..f69dc0de0
--- /dev/null
+++ b/mk/compilation-database.mk
@@ -0,0 +1,11 @@
+compile-commands-json-files :=
+
+define write-compile-commands
+  _srcs := $$(sort $$(foreach src, $$($(1)_SOURCES), $$(src)))
+
+  $(1)_COMPILE_COMMANDS_JSON := $$(addprefix $(buildprefix), $$(addsuffix .compile_commands.json, $$(basename $$(_srcs))))
+
+  compile-commands-json-files += $$($(1)_COMPILE_COMMANDS_JSON)
+
+  clean-files += $$($(1)_COMPILE_COMMANDS_JSON)
+endef
diff --git a/mk/lib.mk b/mk/lib.mk
index fe0add1c9..a002d823f 100644
--- a/mk/lib.mk
+++ b/mk/lib.mk
@@ -68,6 +68,7 @@ include mk/patterns.mk
 include mk/templates.mk
 include mk/cxx-big-literal.mk
 include mk/tests.mk
+include mk/compilation-database.mk
 
 
 # Include all sub-Makefiles.
@@ -97,6 +98,13 @@ $(foreach test-group, $(install-tests-groups), \
     $(eval $(call run-test,$(test),$(install_test_init))) \
     $(eval $(test-group).test-group: $(test).test)))
 
+# Compilation database.
+$(foreach lib, $(libraries), $(eval $(call write-compile-commands,$(lib))))
+$(foreach prog, $(programs), $(eval $(call write-compile-commands,$(prog))))
+
+compile_commands.json: $(compile-commands-json-files)
+	@jq --slurp '.' $^ >$@
+
 # Include makefiles requiring built programs.
 $(foreach mf, $(makefiles-late), $(eval $(call include-sub-makefile,$(mf))))
 
diff --git a/mk/patterns.mk b/mk/patterns.mk
index c81150260..4caa2039e 100644
--- a/mk/patterns.mk
+++ b/mk/patterns.mk
@@ -1,11 +1,41 @@
+
+# These are the complete command lines we use to compile C and C++ files.
+# - $< is the source file.
+# - $1 is the object file to create.
+CC_CMD=$(CC) -o $1 -c $< $(CPPFLAGS) $(GLOBAL_CFLAGS) $(CFLAGS) $($1_CFLAGS) -MMD -MF $(call filename-to-dep,$1) -MP
+CXX_CMD=$(CXX) -o $1 -c $< $(CPPFLAGS) $(GLOBAL_CXXFLAGS_PCH) $(GLOBAL_CXXFLAGS) $(CXXFLAGS) $($1_CXXFLAGS) $(ERROR_SWITCH_ENUM) -MMD -MF $(call filename-to-dep,$1) -MP
+
+# We use COMPILE_COMMANDS_JSON_CMD to turn a compilation command (like CC_CMD
+# or CXX_CMD above) into a comple_commands.json file. We rely on bash native
+# word splitting to define the positional arguments.
+# - $< is the source file being compiled.
+COMPILE_COMMANDS_JSON_CMD=jq --null-input '{ directory: $$ENV.PWD, file: "$<", arguments: $$ARGS.positional }' --args --
+
+
 $(buildprefix)%.o: %.cc
 	@mkdir -p "$(dir $@)"
-	$(trace-cxx) $(CXX) -o $@ -c $< $(CPPFLAGS) $(GLOBAL_CXXFLAGS_PCH) $(GLOBAL_CXXFLAGS) $(CXXFLAGS) $($@_CXXFLAGS) $(ERROR_SWITCH_ENUM) -MMD -MF $(call filename-to-dep, $@) -MP
+	$(trace-cxx) $(call CXX_CMD,$@)
 
 $(buildprefix)%.o: %.cpp
 	@mkdir -p "$(dir $@)"
-	$(trace-cxx) $(CXX) -o $@ -c $< $(CPPFLAGS) $(GLOBAL_CXXFLAGS_PCH) $(GLOBAL_CXXFLAGS) $(CXXFLAGS) $($@_CXXFLAGS) $(ERROR_SWITCH_ENUM) -MMD -MF $(call filename-to-dep, $@) -MP
+	$(trace-cxx) $(call CXX_CMD,$@)
 
 $(buildprefix)%.o: %.c
 	@mkdir -p "$(dir $@)"
-	$(trace-cc) $(CC) -o $@ -c $< $(CPPFLAGS) $(GLOBAL_CFLAGS) $(CFLAGS) $($@_CFLAGS) -MMD -MF $(call filename-to-dep, $@) -MP
+	$(trace-cc) $(call CC_CMD,$@)
+
+# In the following we need to replace the .compile_commands.json extension in $@ with .o
+# to make the object file. This is needed because CC_CMD and CXX_CMD do further expansions
+# based on the object file name (i.e. *_CXXFLAGS and filename-to-dep).
+
+$(buildprefix)%.compile_commands.json: %.cc
+	@mkdir -p "$(dir $@)"
+	$(trace-jq) $(COMPILE_COMMANDS_JSON_CMD) $(call CXX_CMD,$(@:.compile_commands.json=.o)) > $@
+
+$(buildprefix)%.compile_commands.json: %.cpp
+	@mkdir -p "$(dir $@)"
+	$(trace-jq) $(COMPILE_COMMANDS_JSON_CMD) $(call CXX_CMD,$(@:.compile_commands.json=.o)) > $@
+
+$(buildprefix)%.compile_commands.json: %.c
+	@mkdir -p "$(dir $@)"
+	$(trace-jq) $(COMPILE_COMMANDS_JSON_CMD) $(call CC_CMD,$(@:.compile_commands.json=.o)) > $@
diff --git a/mk/tracing.mk b/mk/tracing.mk
index 1fc5573d7..09db1e617 100644
--- a/mk/tracing.mk
+++ b/mk/tracing.mk
@@ -10,6 +10,8 @@ ifeq ($(V), 0)
   trace-install = @echo "  INST  " $@;
   trace-mkdir   = @echo "  MKDIR " $@;
   trace-test    = @echo "  TEST  " $@;
+  trace-sh      = @echo "  SH    " $@;
+  trace-jq      = @echo "  JQ    " $@;
 
   suppress  = @