build: add compile-commands target

It generates a `compile_commands.json` suitable for clangd.
This is almost mandatory to have a command like this one for NixOs
users as tool like bear are not able to intercept correctly the
clang calls due to the usage of a wrapper.

Ticket: #7669

Makefile.am

@@ -18,6 +18,8 @@ DIST_SUBDIRS = $(SUBDIRS) examples/lib/simple examples/lib/custom
 
 CLEANFILES = stamp-h[0-9]*
 
+DISTCLEANFILES = compile_commands.json
+
 install-data-am:
 	@echo "Run 'make install-conf' if you want to install initial configuration files. Or 'make install-full' to install configuration and rules";
 
@@ -71,3 +73,16 @@ install-library:
 
 install-headers:
 	cd src && $(MAKE) $@
+
+compile-commands:
+if HAVE_CLANG
+	$(MAKE) -C src clean
+	TMP_DIR=$$(mktemp -d --suffix=.suricata-compile-commands) && \
+	$(MAKE) EXTRA_CFLAGS="-MJ $$TMP_DIR/\$$*.json" && \
+	echo '[' > $(top_builddir)/compile_commands.json && \
+	cat $$TMP_DIR/*.json >> $(top_builddir)/compile_commands.json && \
+	echo ']' >> $(top_builddir)/compile_commands.json && \
+	rm -rf $$TMP_DIR
+else
+	@echo "clang compile_commands.json generation not supported with current compiler"
+endif

configure.ac

@@ -64,6 +64,8 @@
             ;;
     esac
 
+    AM_CONDITIONAL([HAVE_CLANG], [test "x$compiler" == "xclang"])
+
     # Checks for programs.
     AC_PROG_AWK
     AC_PROG_CC