Rebuild the PLT file when the Erlang/OTP version has changed

plugins/dialyzer.mk

@@ -42,11 +42,17 @@ define filter_opts.erl
 	halt().
 endef
 
+# DIALYZER_PLT is a variable understood directly by Dialyzer.
+#
+# We append the path to erts at the end of the PLT. This works
+# because the PLT file is in the external term format and the
+# function binary_to_term/1 ignores any trailing data.
 $(DIALYZER_PLT): deps app
 	$(eval DEPS_LOG := $(shell test -f $(ERLANG_MK_TMP)/deps.log && \
 		while read p; do test -d $$p/ebin && echo $$p/ebin; done <$(ERLANG_MK_TMP)/deps.log))
 	$(verbose) dialyzer --build_plt $(DIALYZER_PLT_OPTS) --apps \
 		erts kernel stdlib $(PLT_APPS) $(OTP_DEPS) $(LOCAL_DEPS) $(DEPS_LOG) || test $$? -eq 2
+	$(verbose) $(ERL) -eval 'io:format("~n~s~n", [code:lib_dir(erts)]), halt().' >> $@
 
 plt: $(DIALYZER_PLT)
 
@@ -55,6 +61,11 @@ distclean-plt:
 
 ifneq ($(wildcard $(DIALYZER_PLT)),)
 dialyze: $(if $(filter --src,$(DIALYZER_DIRS)),,deps app)
+	$(verbose) if ! tail -n1 $(DIALYZER_PLT) | \
+		grep -q "^`$(ERL) -eval 'io:format("~s", [code:lib_dir(erts)]), halt().'`$$"; then \
+		rm $(DIALYZER_PLT); \
+		$(MAKE) plt; \
+	fi
 else
 dialyze: $(DIALYZER_PLT)
 endif