[EEP 78] Implement erl_eval for multi map-comprehensions

lib/stdlib/src/erl_eval.erl

@@ -1253,30 +1253,37 @@ eval_bc1(E, [], Bs, Lf, Ef, FUVs, Acc) ->
     {value,V,_} = expr(E, Bs, Lf, Ef, none, FUVs),
     <<Acc/bitstring,V/bitstring>>.
 
-%% eval_mc(Expr, [Qualifier], Bindings, LocalFunctionHandler,
+%% eval_mc(ExprOrExprs, [Qualifier], Bindings, LocalFunctionHandler,
 %%         ExternalFuncHandler, RetBindings) ->
 %%	{value,Value,Bindings} | Value
 
-eval_mc(E, Qs, Bs, Lf, Ef, RBs, FUVs) ->
-    L = eval_mc1(E, Qs, Bs, Lf, Ef, FUVs, []),
+eval_mc(Es, Qs, Bs, Lf, Ef, RBs, FUVs) when is_list(Es) ->
+    L = eval_mc1(Es, Qs, Bs, Lf, Ef, FUVs, []),
     Map = maps:from_list(reverse(L)),
-    ret_expr(Map, Bs, RBs).
+    ret_expr(Map, Bs, RBs);
+eval_mc(E, Qs, Bs, Lf, Ef, RBs, FUVs) ->
+    eval_mc([E], Qs, Bs, Lf, Ef, RBs, FUVs).
 
-eval_mc1(E, [{zip, Anno, Gens}|Qs], Bs0, Lf, Ef, FUVs, Acc0) ->
+eval_mc1(Es, [{zip, Anno, Gens}|Qs], Bs0, Lf, Ef, FUVs, Acc0) ->
     {VarList, Bs1} = convert_gen_values(Gens, [], Bs0, Lf, Ef, FUVs),
-    eval_zip(E, [{zip, Anno, VarList}|Qs], Bs1, Lf, Ef, FUVs, Acc0, fun eval_mc1/7);
-eval_mc1(E, [Q|Qs], Bs0, Lf, Ef, FUVs, Acc0) ->
+    eval_zip(Es, [{zip, Anno, VarList}|Qs], Bs1, Lf, Ef, FUVs, Acc0, fun eval_mc1/7);
+eval_mc1(Es, [Q|Qs], Bs0, Lf, Ef, FUVs, Acc0) ->
     case is_generator(Q) of
         true ->
-            CF = fun(Bs, Acc) -> eval_mc1(E, Qs, Bs, Lf, Ef, FUVs, Acc) end,
+            CF = fun(Bs, Acc) -> eval_mc1(Es, Qs, Bs, Lf, Ef, FUVs, Acc) end,
             eval_generator(Q, Bs0, Lf, Ef, FUVs, Acc0, CF);
         false ->
-            CF = fun(Bs) -> eval_mc1(E, Qs, Bs, Lf, Ef, FUVs, Acc0) end,
+            CF = fun(Bs) -> eval_mc1(Es, Qs, Bs, Lf, Ef, FUVs, Acc0) end,
             eval_filter(Q, Bs0, Lf, Ef, CF, FUVs, Acc0)
     end;
-eval_mc1({map_field_assoc,Lfa,K0,V0}, [], Bs, Lf, Ef, FUVs, Acc) ->
-    {value,KV,_} = expr({tuple,Lfa,[K0,V0]}, Bs, Lf, Ef, none, FUVs),
-    [KV|Acc].
+eval_mc1(Es, [], Bs, Lf, Ef, FUVs, Acc) ->
+    eval_mc2(Es, Bs, Lf, Ef, FUVs, Acc).
+
+eval_mc2([{map_field_assoc,_,K0,V0}|Es], Bs, Lf, Ef, FUVs, Acc) ->
+    {[K,V],_} = expr_list([K0,V0], Bs, Lf, Ef, FUVs),
+    eval_mc2(Es, Bs, Lf, Ef, FUVs, [{K,V}|Acc]);
+eval_mc2([], _Bs, _Lf, _Ef, _FUVs, Acc) ->
+    Acc.
 
 eval_zip(E, [{zip, Anno, VarList}|Qs], Bs0, Lf, Ef, FUVs, Acc0, Fun) ->
     Gens = case check_bad_generators(VarList, {Bs0, Lf, Ef}, []) of

lib/stdlib/src/erl_lint.erl

@@ -402,6 +402,8 @@ format_error_1(update_literal) ->
     ~"expression updates a literal";
 format_error_1(illegal_zip_generator) ->
     ~"only generators are allowed in a zip generator.";
+format_error_1(illegal_map_exact_in_comprehension) ->
+    ~"illegal map association, did you mean to use `=>`?";
 %% --- patterns and guards ---
 format_error_1(illegal_map_assoc_in_pattern) -> ~"illegal pattern, did you mean to use `:=`?";
 format_error_1(illegal_pattern) -> ~"illegal pattern";
@@ -4060,6 +4062,9 @@ comprehension_exprs(E, Vt, St) ->
 
 comprehension_expr({map_field_assoc,_,K,V}, Vt0, St0) ->
     expr_list([K,V], Vt0, St0);
+comprehension_expr({map_field_exact,A,K,V}, Vt0, St0) ->
+    St = add_error(A, illegal_map_exact_in_comprehension, St0),
+    expr_list([K,V], Vt0, St);
 comprehension_expr(E, Vt, St) ->
     expr(E, Vt, St).
 

lib/stdlib/test/erl_eval_SUITE.erl

@@ -33,6 +33,7 @@
          zbc/1,
          zmc/1,
          multi_lc/1,
+         multi_mc/1,
          simple_cases/1,
          unary_plus/1,
          apply_atom/1,
@@ -105,7 +106,7 @@ all() ->
      funs, custom_stacktrace, try_catch, eval_expr_5, zero_width,
      eep37, eep43, otp_15035, otp_16439, otp_14708, otp_16545, otp_16865,
      eep49, binary_and_map_aliases, eep58, strict_generators, binary_skip,
-     zlc, zbc, zmc, multi_lc].
+     zlc, zbc, zmc, multi_lc, multi_mc].
 
 groups() ->
     [].
@@ -447,6 +448,16 @@ multi_lc(Config) when is_list(Config) ->
           "[1, 2 || _ <- [1, 2]].",
           [1, 2, 1, 2]).
 
+multi_mc(Config) when is_list(Config) ->
+    check(fun() -> #{A => B || X <- [1, 5], {A, B} <- [{X, X+1}, {X+2, X+3}]} end,
+        "#{X => X+1, X+2 => X+3 || X <- [1, 5]}.",
+        #{1 => 2, 3 => 4, 5 => 6, 7 => 8}),
+    check(fun() -> #{A => B || X <- [1, 5], {A, B} <- [{X, X+1}, {X, X+3}]} end,
+        "#{X => X+1, X => X+3 || X <- [1, 5]}.",
+        #{1 => 4, 5 => 8}),
+    error_check("#{1 := 2 || _ <- []}.", illegal_map_exact_in_comprehension),
+    error_check("#{1 => 2, 3 := 4 || _ <- []}.", illegal_map_exact_in_comprehension).
+
 %% Simple cases, just to cover some code.
 simple_cases(Config) when is_list(Config) ->
     check(fun() -> A = $C end, "A = $C.", $C),