core_pp: Correct printing of map literals

A map key in a pattern would be incorrectly pretty-printed.
As an example, the pattern in:

  x() ->
    #{ #{ a => 3 } := 42 } = X.

would be pretty-printed as:

    <~{~<~{~<'a',3>}~,42>}~

instead of:

    <~{~<~{::<'a',3>}~,42>}~

When this problem has been corrected, the workaround for it in
cerl:ann_c_map/3 can be removed. The workaround was not harmless,
as it would cause the following map update to incorrectly succeed:

  (#{})#{a:=1}

3 files changed, 14 insertions, 14 deletions

diff --git a/lib/compiler/src/cerl.erl b/lib/compiler/src/cerl.erl
index 96c8e02542..705c87539e 100644
--- a/lib/compiler/src/cerl.erl
+++ b/lib/compiler/src/cerl.erl
@@ -1617,18 +1617,6 @@ ann_c_map(As, Es) ->
 
 -spec ann_c_map([term()], c_map() | c_literal(), [c_map_pair()]) -> c_map() | c_literal().
 
-ann_c_map(As,#c_literal{val=Mval}=M,Es) when is_map(Mval), map_size(Mval) =:= 0 ->
-    Pairs = [[Ck,Cv]||#c_map_pair{key=Ck,val=Cv}<-Es],
-    IsLit = lists:foldl(fun(Pair,Res) ->
-		Res andalso is_lit_list(Pair)
-	end, true, Pairs),
-    Fun = fun(Pair) -> [K,V] = lit_list_vals(Pair), {K,V} end,
-    case IsLit of
-	false ->
-	    #c_map{arg=M, es=Es, anno=As };
-	true ->
-	    #c_literal{anno=As, val=maps:from_list(lists:map(Fun, Pairs))}
-	end;
 ann_c_map(As,#c_literal{val=M},Es) when is_map(M) ->
     fold_map_pairs(As,Es,M);
 ann_c_map(As,M,Es) ->
diff --git a/lib/compiler/src/core_pp.erl b/lib/compiler/src/core_pp.erl
index 03801a9b6d..01922c3fdf 100644
--- a/lib/compiler/src/core_pp.erl
+++ b/lib/compiler/src/core_pp.erl
@@ -184,12 +184,12 @@ format_1(#c_map{arg=Var,es=Es}, Ctxt) ->
     ];
 format_1(#c_map_pair{op=#c_literal{val=assoc},key=K,val=V}, Ctxt) ->
     ["::<",
-     format_hseq([K,V], ",", add_indent(Ctxt, 1), fun format/2),
+     format_map_pair(K, V, Ctxt),
      ">"
     ];
 format_1(#c_map_pair{op=#c_literal{val=exact},key=K,val=V}, Ctxt) ->
     ["~<",
-     format_hseq([K,V], ",", add_indent(Ctxt, 1), fun format/2),
+     format_map_pair(K, V, Ctxt),
      ">"
     ];
 format_1(#c_cons{hd=H,tl=T}, Ctxt) ->
@@ -448,6 +448,12 @@ format_list_tail(#c_cons{anno=[],hd=H,tl=T}, Ctxt) ->
 format_list_tail(Tail, Ctxt) ->
     ["|",format(Tail, add_indent(Ctxt, 1)),"]"].
 
+format_map_pair(K, V, Ctxt0) ->
+    Ctxt1 = add_indent(Ctxt0, 1),
+    Txt = format(K, set_class(Ctxt1, expr)),
+    Ctxt2 = add_indent(Ctxt0, width(Txt, Ctxt1)),
+    [Txt,",",format(V, Ctxt2)].
+
 indent(Ctxt) -> indent(Ctxt#ctxt.indent, Ctxt).
 
 indent(N, _) when N =< 0 -> "";
diff --git a/lib/compiler/test/map_SUITE.erl b/lib/compiler/test/map_SUITE.erl
index dbac61765b..bc5ae803c6 100644
--- a/lib/compiler/test/map_SUITE.erl
+++ b/lib/compiler/test/map_SUITE.erl
@@ -319,6 +319,12 @@ t_update_exact(Config) when is_list(Config) ->
     {'EXIT',{badarg,_}} = (catch M0#{42=>v1,42.0:=v2,42:=v3}),
     {'EXIT',{badarg,_}} = (catch <<>>#{nonexisting:=val}),
     {'EXIT',{badarg,_}} = (catch M0#{<<0:257>> := val}), %% limitation
+
+    %% A workaround for a bug allowed an empty map to be updated.
+    {'EXIT',{badarg,_}} = (catch (id(#{}))#{a:=1}),
+    {'EXIT',{badarg,_}} = (catch #{}#{a:=1}),
+    Empty = #{},
+    {'EXIT',{badarg,_}} = (catch Empty#{a:=1}),
     ok.
 
 t_update_values(Config) when is_list(Config) ->