Delete existing out-edges before adding new ones in modify_erlcinfo

When the source file changes it could happen that some of its
dependecies get removed.  In that case we should remove these
former dependencies from the graph, so that they don't influence
recompilation of the source file anymore.

inttest/erlc_dep_graph/erlc_dep_graph_rt.erl

@@ -40,7 +40,7 @@ files() ->
 run(_Dir) ->
     compile_all(ok, ""),
     check_beams_ok(),
-    check_beams_untouched(),
+    check_beams_untouched(filelib:wildcard("ebin/*.beam")),
     modify_and_recompile_ok("src/lisp.erl", "ebin/lisp.beam"),
 
     clean_all_ok(),
@@ -48,14 +48,27 @@ run(_Dir) ->
     compile_all(ok, ""),
     modify_and_recompile_ok("extra_include/extra.hrl", "ebin/java.beam"),
 
+    Java = "src/java.erl",
+    {ok, OrigContent} = file:read_file(Java),
+    %% Remove header file inclusion
+    {ok, _} = file:copy("src/java.erl.no_extra", Java),
+    %% Ensure recompilation
+    touch([Java]),
+    compile_all(ok, ""),
+    %% Modify that header file
+    touch(["extra_include/extra.hrl"]),
+    %% Ensure we don't have to recompile anything
+    check_beams_untouched(["ebin/java.beam"]),
+    %% Clean up
+    ok = file:write_file(Java, OrigContent),
+
     ok.
 
 check_beams_ok() ->
     F = fun(BeamFile) -> ?assert(filelib:is_regular(BeamFile)) end,
     with_erl_beams(F).
 
-check_beams_untouched() ->
-    Beams = filelib:wildcard("ebin/*.beam"),
+check_beams_untouched(Beams) ->
     compile_all_and_assert_mtimes(Beams, fun erlang:'=:='/2).
 
 modify_and_recompile_ok(TouchFile, CheckFile) ->

inttest/erlc_dep_graph/src/java.erl.no_extra

@@ -0,0 +1,10 @@
+%% -*- mode: erlang;erlang-indent-level: 4;indent-tabs-mode: nil -*-
+%% ex: ts=4 sw=4 ft=erlang et
+-module(java).
+
+-export([factory/0]).
+
+-include("lambda.hrl").
+
+factory() ->
+	?FUN.

src/rebar_erlc_compiler.erl

@@ -448,6 +448,7 @@ modify_erlcinfo(G, Source, Dirs) ->
     ok = file:close(Fd),
     LastUpdated = {date(), time()},
     digraph:add_vertex(G, Source, LastUpdated),
+    digraph:del_edges(G, digraph:out_edges(G, Source)),
     lists:foreach(
       fun(Incl) ->
               update_erlcinfo(G, Dirs, Incl),