common.mak: add compdb Makefile target

Add a new Makefile target 'compdb' to create the compilation database
'compile_commands.json' [1]. This file can then be used by the language
server 'clangd' [2], which is a possible backend for the so called
'Language Server Protocol' (LSP) [3] used by many IDEs and editors.

In addition, add this file to `.gitignore`.

[1] https://clang.llvm.org/docs/JSONCompilationDatabase.html
[2] https://clangd.llvm.org/
[3] https://microsoft.github.io/language-server-protocol/

Reviewed-by: Jan Höppner <hoeppner@linux.ibm.com>
Signed-off-by: Marc Hartmayer <mhartmay@linux.ibm.com>
Signed-off-by: Jan Höppner <hoeppner@linux.ibm.com>

common.mak

@@ -360,6 +360,7 @@ help:
 	@echo '  all      Build all tools (default target)'
 	@echo '  install  Install tools'
 	@echo '  clean    Delete all generated files'
+	@echo '  compdb   Generate compile_commands.json for clangd'
 	@echo ''
 	@echo 'OPTIONS'
 	@echo '  D=1      	 Build with debugging option "-Og"'
@@ -375,6 +376,27 @@ help:
 	@echo '  # make C=1 CHECK=smatch'
 .PHONY: help
 
+
+# 'compile_commands.json' generation
+#
+# Create the compilation database 'compile_commands.json'. See
+# https://clang.llvm.org/docs/JSONCompilationDatabase.html for details.
+#
+.PHONY: compdb
+compdb:
+	$(MAKE) clean
+ifneq ($(shell command -v compiledb),)
+	compiledb $(MAKE)
+else ifneq ($(shell command -v bear),)
+  ifeq ($(shell bear --help|grep -- '-- ...'),)
+	bear $(MAKE)
+  else
+	bear -- $(MAKE)
+  endif
+else
+	$(error Please install either 'compiledb' or 'bear')
+endif
+
 # Automatic dependency generation
 #
 # Create ".o.d" dependency files with the -MM compile option for all ".c" and