Snapshot -- imprecise error message with union of maps

Summary: An example where error messages choose a bad candidate with a union of maps.

Reviewed By: sopotc

Differential Revision: D69980767

fbshipit-source-id: 5b018000056cb33744b5cf4f859a41a1d1b0c519

Author: VLanvin

crates/elp/src/resources/test/eqwalizer_tests/check/error_messages.pretty

@@ -0,0 +1,28 @@
+error: incompatible_types (See https://fb.me/eqwalizer_errors#incompatible_types)
+   ┌─ check/src/error_messages.erl:16:22
+   │
+16 │ map_candidates(M) -> M.
+   │                      ^
+   │                      │
+   │                      M.
+Expression has type:   #{bar := atom(), baz := atom()}
+Context expected type: foo_map() | #{foo => atom()}
+   │                      
+
+Because in the expression's type:
+  Here the type is:     #{baz := ...}
+  Context expects type: #{...}
+  The expected map has no corresponding key for: baz.
+
+------------------------------ Detailed message ------------------------------
+
+  #{bar := atom(), baz := atom()} is not compatible with foo_map() | #{foo => atom()}
+  because
+  #{bar := atom(), baz := atom()} is not compatible with foo_map()
+  because
+  #{bar := atom(), baz := atom()} is not compatible with #{bar => atom(), baz => number(), other => atom(), other2 => atom(), other3 => atom(), other4 => atom(), other5 => atom()}
+  because
+  at key `baz`:
+  #{bar := atom(), baz := atom()} is not compatible with #{bar => atom(), baz => number(), other => atom(), other2 => atom(), other3 => atom(), other4 => atom(), other5 => atom()}
+
+1 ERROR

test_projects/eqwalizer_tests/check/src/error_messages.erl

@@ -0,0 +1,16 @@
+-module(error_messages).
+
+-compile([export_all, nowarn_export_all]).
+
+-type foo_map() :: #{
+    bar => atom(),
+    baz => integer(),
+    other => atom(),
+    other2 => atom(),
+    other3 => atom(),
+    other4 => atom(),
+    other5 => atom()}.
+
+-spec map_candidates(#{bar := atom(), baz := atom()}) ->
+    foo_map() | #{foo => atom()}.
+map_candidates(M) -> M.