- builder.rb: fix hash value omission considering some local vars as constants (#1064)

A constant always start in uppercase but a local will not always
start with lowercase. `_foo` and `💎` are both valid local variables.

Author: Earlopain

lib/parser/builders/default.rb

@@ -524,10 +524,10 @@ def pair_label(key_t)
 
       label = value(key_t)
       value =
-        if label =~ /\A[[:lower:]]/
-          n(:ident, [ label.to_sym ], Source::Map::Variable.new(value_l))
-        else
+        if label =~ /\A[[:upper:]]/
           n(:const, [ nil, label.to_sym ], Source::Map::Constant.new(nil, value_l, value_l))
+        else
+          n(:ident, [ label.to_sym ], Source::Map::Variable.new(value_l))
         end
       pair_keyword(key_t, accessible(value))
     end

test/test_parser.rb

@@ -10241,6 +10241,30 @@ def test_hash_pair_value_omission
         | ~~~~~ expression (pair)},
       SINCE_3_1)
 
+    assert_parses(
+      s(:begin,
+        s(:lvasgn, :foo,
+          s(:int, 1)),
+        s(:hash,
+          s(:pair,
+            s(:sym, :foo),
+            s(:lvar, :foo)))),
+      %q{foo = 1; {foo:}},
+      %q{},
+      SINCE_3_1)
+
+    assert_parses(
+      s(:begin,
+        s(:lvasgn, :_foo,
+          s(:int, 1)),
+        s(:hash,
+          s(:pair,
+            s(:sym, :_foo),
+            s(:lvar, :_foo)))),
+      %q{_foo = 1; {_foo:}},
+      %q{},
+      SINCE_3_1)
+
     assert_parses(
       s(:hash,
         s(:pair, s(:sym, :BAR), s(:const, nil, :BAR))),