EEP-23: Allow variables in fun M:F/A

Currently, the external fun syntax "fun M:F/A" only supports
literals. That is, "fun lists:reverse/1" is allowed but not
"fun M:F/A".

In many real-life situations, some or all of M, F, A are
not known until run-time, and one is forced to either use
the undocumented erlang:make_fun/3 BIF or to use a
"tuple fun" (which is deprecated).

EEP-23 suggests that the parser (erl_parse) should immediately
transform "fun M:F/A" to "erlang:make_fun(M, F, A)". We have
not followed that approach in this implementation, because we
want the abstract code to mirror the source code as closely
as possible, and we also consider erlang:make_fun/3 to
be an implementation detail that we might want to remove in
the future.

Instead, we will change the abstract format for "fun M:F/A" (in a way
that is not backwards compatible), and while we are at it, we will
move the translation from "fun M:F/A" to "erlang:make_fun(M, F, A)"
from sys_pre_expand down to the v3_core pass. We will also update
the debugger and xref to use the new format.

We did consider making the abstract format backward compatible if
no variables were used in the fun, but decided against it. Keeping
it backward compatible would mean that there would be different
abstract formats for the no-variable and variable case, and tools
would have to handle both formats, probably forever.

Reference: http://www.erlang.org/eeps/eep-0023.html

4 files changed, 118 insertions, 12 deletions

diff --git a/lib/tools/src/xref_reader.erl b/lib/tools/src/xref_reader.erl
index d22f0df164..92f0c45c7b 100644
--- a/lib/tools/src/xref_reader.erl
+++ b/lib/tools/src/xref_reader.erl
@@ -158,15 +158,20 @@ expr({'try',_Line,Es,Scs,Ccs,As}, S) ->
     S2 = clauses(Scs, S1),
     S3 = clauses(Ccs, S2),
     expr(As, S3);
-expr({call, Line,
-      {remote, _, {atom,_,erlang}, {atom,_,make_fun}},
-      [{atom,_,Mod}, {atom,_,Fun}, {integer,_,Arity}]}, S) ->
-    %% Added in R10B-6. M:F/A.
-    expr({'fun', Line, {function, Mod, Fun, Arity}}, S);
-expr({'fun', Line, {function, Mod, Name, Arity}}, S) ->
-    %% Added in R10B-6. M:F/A.
+expr({'fun', Line, {function, {atom,_,Mod},
+		    {atom,_,Name},
+		    {integer,_,Arity}}}, S) ->
+    %% New format in R15. M:F/A (literals).
     As = lists:duplicate(Arity, {atom, Line, foo}),
     external_call(Mod, Name, As, Line, false, S);
+expr({'fun', Line, {function, Mod, Name, {integer,_,Arity}}}, S) ->
+    %% New format in R15. M:F/A (one or more variables).
+    As = lists:duplicate(Arity, {atom, Line, foo}),
+    external_call(erlang, apply, [Mod, Name, list2term(As)], Line, true, S);
+expr({'fun', Line, {function, Mod, Name, _Arity}}, S) ->
+    %% New format in R15. M:F/A (one or more variables).
+    As = {var, Line, '_'},
+    external_call(erlang, apply, [Mod, Name, As], Line, true, S);
 expr({'fun', Line, {function, Name, Arity}, _Extra}, S) ->
     %% Added in R8.
     handle_call(local, S#xrefr.module, Name, Arity, Line, S);
@@ -286,10 +291,10 @@ check_funarg(W, ArgsList, Line, S) ->
     expr(ArgsList, S1).
 
 funarg({'fun', _, _Clauses, _Extra}, _S) -> true;
-funarg({var, _, Var}, S) -> member(Var, S#xrefr.funvars);
-funarg({call,_,{remote,_,{atom,_,erlang},{atom,_,make_fun}},_MFA}, _S) ->
-    %% R10B-6. M:F/A.
+funarg({'fun', _, {function,_,_,_}}, _S) ->
+    %% New abstract format for fun M:F/A in R15.
     true;
+funarg({var, _, Var}, S) -> member(Var, S#xrefr.funvars);
 funarg(_, _S) -> false.
 
 fun_args(apply2, [FunArg, Args]) -> {FunArg, Args};
diff --git a/lib/tools/test/xref_SUITE.erl b/lib/tools/test/xref_SUITE.erl
index 2f83ab4995..e0876381ca 100644
--- a/lib/tools/test/xref_SUITE.erl
+++ b/lib/tools/test/xref_SUITE.erl
@@ -46,7 +46,8 @@
 -export([
 	 add/1, default/1, info/1, lib/1, read/1, read2/1, remove/1,
 	 replace/1, update/1, deprecated/1, trycatch/1,
-         abstract_modules/1, fun_mfa/1, qlc/1]).
+         abstract_modules/1, fun_mfa/1, fun_mfa_r14/1,
+	 fun_mfa_vars/1, qlc/1]).
 
 -export([
 	 analyze/1, basic/1, md/1, q/1, variables/1, unused_locals/1]).
@@ -82,7 +83,7 @@ groups() ->
      {files, [],
       [add, default, info, lib, read, read2, remove, replace,
        update, deprecated, trycatch, abstract_modules, fun_mfa,
-       qlc]},
+       fun_mfa_r14, fun_mfa_vars, qlc]},
      {analyses, [],
       [analyze, basic, md, q, variables, unused_locals]},
      {misc, [], [format_error, otp_7423, otp_7831]}].
@@ -1771,6 +1772,88 @@ fun_mfa(Conf) when is_list(Conf) ->
     ?line ok = file:delete(Beam),
     ok.
 
+%% Same as the previous test case, except that we use a BEAM file
+%% that was compiled by an R14 compiler to test backward compatibility.
+fun_mfa_r14(Conf) when is_list(Conf) ->
+    Dir = ?config(data_dir, Conf),
+    MFile = fname(Dir, "fun_mfa_r14"),
+
+    A = fun_mfa_r14,
+    {ok, _} = xref:start(s),
+    {ok, A} = xref:add_module(s, MFile, {warnings,false}),
+    {ok, [{{{A,t,0},{'$M_EXPR','$F_EXPR',0}},[7]},
+	  {{{A,t,0},{A,t,0}},[6]},
+	  {{{A,t1,0},{'$M_EXPR','$F_EXPR',0}},[11]},
+	  {{{A,t1,0},{A,t,0}},[10]},
+	  {{{A,t2,0},{A,t,0}},[14]},
+	  {{{A,t3,0},{A,t3,0}},[17]}]} =
+        xref:q(s, "(Lin) E"),
+
+    ok = check_state(s),
+    xref:stop(s),
+
+    ok.
+
+%% fun M:F/A with varibles.
+fun_mfa_vars(Conf) when is_list(Conf) ->
+    Dir = ?copydir,
+    File = fname(Dir, "fun_mfa_vars.erl"),
+    MFile = fname(Dir, "fun_mfa_vars"),
+    Beam = fname(Dir, "fun_mfa_vars.beam"),
+    Test = <<"-module(fun_mfa_vars).
+
+              -export([t/1, t1/1, t2/3]).
+
+              t(Mod) ->
+                  F = fun Mod:bar/2,
+                  (F)(a, b).
+
+              t1(Name) ->
+                  F = fun ?MODULE:Name/1,
+                  (F)(a).
+
+              t2(Mod, Name, Arity) ->
+                  F = fun Mod:Name/Arity,
+                  (F)(a).
+
+              t3(Arity) ->
+                  F = fun ?MODULE:t/Arity,
+                  (F)(1, 2, 3).
+
+              t4(Mod, Name) ->
+                  F = fun Mod:Name/3,
+                  (F)(a, b, c).
+
+              t5(Mod, Arity) ->
+                  F = fun Mod:t/Arity,
+                  (F)().
+             ">>,
+
+    ok = file:write_file(File, Test),
+    A = fun_mfa_vars,
+    {ok, A} = compile:file(File, [report,debug_info,{outdir,Dir}]),
+    {ok, _} = xref:start(s),
+    {ok, A} = xref:add_module(s, MFile, {warnings,false}),
+    {ok, [{{{A,t,1},{'$M_EXPR','$F_EXPR',2}},[7]},
+	  {{{A,t,1},{'$M_EXPR',bar,2}},[6]},
+	  {{{A,t1,1},{'$M_EXPR','$F_EXPR',1}},[11]},
+	  {{{A,t1,1},{A,'$F_EXPR',1}},[10]},
+	  {{{A,t2,3},{'$M_EXPR','$F_EXPR',-1}},[14]},
+	  {{{A,t2,3},{'$M_EXPR','$F_EXPR',1}},[15]},
+	  {{{A,t3,1},{'$M_EXPR','$F_EXPR',3}},[19]},
+	  {{{A,t3,1},{fun_mfa_vars,t,-1}},[18]},
+	  {{{A,t4,2},{'$M_EXPR','$F_EXPR',3}},[22,23]},
+	  {{{A,t5,2},{'$M_EXPR','$F_EXPR',0}},[27]},
+	  {{{A,t5,2},{'$M_EXPR',t,-1}},[26]}]} =
+	xref:q(s, "(Lin) E"),
+
+    ok = check_state(s),
+    xref:stop(s),
+
+    ok = file:delete(File),
+    ok = file:delete(Beam),
+    ok.
+
 qlc(suite) -> [];
 qlc(doc) -> ["OTP-5195: A bug fix when using qlc:q/1,2."];
 qlc(Conf) when is_list(Conf) ->
diff --git a/lib/tools/test/xref_SUITE_data/fun_mfa_r14.beam b/lib/tools/test/xref_SUITE_data/fun_mfa_r14.beam
new file mode 100644
index 0000000000..4645525690
--- /dev/null
+++ b/lib/tools/test/xref_SUITE_data/fun_mfa_r14.beam
diff --git a/lib/tools/test/xref_SUITE_data/fun_mfa_r14.erl b/lib/tools/test/xref_SUITE_data/fun_mfa_r14.erl
new file mode 100644
index 0000000000..293bd83a8b
--- /dev/null
+++ b/lib/tools/test/xref_SUITE_data/fun_mfa_r14.erl
@@ -0,0 +1,18 @@
+-module(fun_mfa_r14).
+
+-export([t/0, t1/0, t2/0, t3/0]).
+
+t() ->
+    F = fun ?MODULE:t/0,
+    (F)().
+
+t1() ->
+    F = fun t/0,
+    (F)().
+
+t2() ->
+    fun ?MODULE:t/0().
+
+t3() ->
+    fun t3/0().
+