Add typer target

This patch adds a typer target to the Makefile. It makes it
easier for developers to start adding specs to the codebase. It
also as a build_plt target with the built-in applications typer
needs to analyze rebar.

This also includes the Erlang version in the generated PLT file.
typer and dialyzer targets use this file. Finally, the distclean
target removed the versioned PLT file.

Makefile

@@ -2,6 +2,9 @@
 
 REBAR=$(PWD)/rebar
 RETEST=$(PWD)/deps/retest/retest
+OTPVSNCMD='io:fwrite("~s",[rebar_utils:otp_release()]), halt().'
+OTPVSN = $(shell erl -pa ebin/ -noshell -eval $(OTPVSNCMD))
+PLT_FILENAME=~/.dialyzer_rebar_$(OTPVSN)_plt
 
 all:
 	./bootstrap
@@ -13,6 +16,7 @@ clean:
 distclean: clean
 	@rm -f dialyzer_warnings
 	@rm -rf deps
+	@rm -f ~/.dialyzer_rebar_*_plt
 
 debug:
 	@./bootstrap debug
@@ -22,12 +26,35 @@ check: debug xref dialyzer deps test
 xref:
 	@./rebar xref
 
+build_plt:
+	-dialyzer --build_plt --output_plt $(PLT_FILENAME) --apps \
+		erts \
+		kernel \
+		stdlib \
+		crypto \
+		compiler \
+		asn1 \
+		eunit \
+		tools \
+		ssl \
+		edoc \
+		reltool \
+		snmp \
+		sasl
+	-dialyzer --add_to_plt --output_plt $(PLT_FILENAME) --apps diameter
+
 dialyzer: dialyzer_warnings
 	@diff -U0 dialyzer_reference dialyzer_warnings
 
 dialyzer_warnings:
-	-@dialyzer -q -nn -n ebin -Wunmatched_returns -Werror_handling \
+	-@dialyzer --plt $(PLT_FILENAME) -q -nn -n ebin \
-		-Wrace_conditions > dialyzer_warnings
+		-Wunmatched_returns \
+		-Werror_handling \
+		-Wrace_conditions \
+		> dialyzer_warnings
+
+typer:
+	typer -r --plt $(PLT_FILENAME) ./src -I ./include
 
 binary: VSN = $(shell ./rebar -V)
 binary: clean all