File 7691-Improve-illegal-pattern-error-for-accidental-map-ass.patch of Package erlang

From 6db7d96589b97842044bd79f1db4d0efbc60086a Mon Sep 17 00:00:00 2001
From: Johannes Christ <jc@jchri.st>
Date: Sat, 25 May 2024 08:17:42 +0200
Subject: [PATCH] Improve illegal pattern error for accidental map associations

Given a module such as this:

    -module(test).
    -export([pattern/1]).

    pattern(#{foo => bar}) -> ok.

We presently report an error as:

    test.erl:4:15: illegal pattern
    %    4| pattern(#{foo => bar}) -> ok.
    %     |               ^

Since we have information in `erl_lint` on the bad pattern being a map
field update, we can be a bit more helpful by extending the error with a
hint instructing the user that `:=` is most likely wanted instead:

    test.erl:4:15: illegal pattern, did you mean to use `:=`?
    %    4| pattern(#{foo => bar}) -> ok.
    %     |               ^
---
 lib/stdlib/src/erl_lint.erl        | 3 ++-
 lib/stdlib/test/erl_lint_SUITE.erl | 4 ++--
 2 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/lib/stdlib/src/erl_lint.erl b/lib/stdlib/src/erl_lint.erl
index 20f3162cd8..d8825d677a 100644
--- a/lib/stdlib/src/erl_lint.erl
+++ b/lib/stdlib/src/erl_lint.erl
@@ -327,6 +327,7 @@ format_error({too_many_arguments,Arity}) ->
 format_error(update_literal) ->
     "expression updates a literal";
 %% --- patterns and guards ---
+format_error(illegal_map_assoc_in_pattern) -> "illegal pattern, did you mean to use `:=`?";
 format_error(illegal_pattern) -> "illegal pattern";
 format_error(illegal_map_key) -> "illegal map key in pattern";
 format_error(illegal_bin_pattern) ->
@@ -2047,7 +2048,7 @@ is_pattern_expr_1(_Other) -> false.
 
 pattern_map(Ps, Vt0, Old, St0) ->
     foldl(fun({map_field_assoc,A,_,_}, {Psvt,Psnew,St1}) ->
-                  {Psvt,Psnew,add_error(A, illegal_pattern, St1)};
+                  {Psvt,Psnew,add_error(A, illegal_map_assoc_in_pattern, St1)};
              ({map_field_exact,_A,K,V}, {Psvt,Psnew,St1}) ->
                   St2 = St1#lint{gexpr_context=map_key},
                   {Kvt, St3} = gexpr(K, Vt0, St2),
diff --git a/lib/stdlib/test/erl_lint_SUITE.erl b/lib/stdlib/test/erl_lint_SUITE.erl
index 5c36031ed4..ffeb7c2e11 100644
--- a/lib/stdlib/test/erl_lint_SUITE.erl
+++ b/lib/stdlib/test/erl_lint_SUITE.erl
@@ -4070,7 +4070,7 @@ maps(Config) ->
              {{4,24},erl_lint,illegal_map_construction},
              {{8,36},erl_lint,illegal_map_construction}],
             [{{5,20},erl_lint,update_literal}]}},
-          {illegal_pattern,
+          {illegal_map_assoc_in_pattern,
            <<"t(#{ a := A,
                    c => d,
                    e := F,
@@ -4082,7 +4082,7 @@ maps(Config) ->
                   {A,F}.
             ">>,
            [],
-           {errors,[{{2,22},erl_lint,illegal_pattern},
+           {errors,[{{2,22},erl_lint,illegal_map_assoc_in_pattern},
                     {{7,28},erl_lint,illegal_pattern}],
             []}},
           {error_in_illegal_map_construction,
-- 
2.35.3