Hash#inspect with colon style

hash.c

@@ -3405,20 +3405,65 @@ rb_hash_to_a(VALUE hash)
     return ary;
 }
 
+static bool
+symbol_key_needs_quote(VALUE str)
+{
+    long len = RSTRING_LEN(str);
+    if (len == 0 || !rb_str_symname_p(str)) return true;
+    const char *s = RSTRING_PTR(str);
+    char first = s[0];
+    if (first == '@' || first == '$' || first == '!') return true;
+    if (!at_char_boundary(s, s + len - 1, RSTRING_END(str), rb_enc_get(str))) return false;
+    switch (s[len - 1]) {
+        case '+':
+        case '-':
+        case '*':
+        case '/':
+        case '`':
+        case '%':
+        case '^':
+        case '&':
+        case '|':
+        case ']':
+        case '<':
+        case '=':
+        case '>':
+        case '~':
+        case '@':
+            return true;
+        default:
+            return false;
+    }
+}
+
 static int
 inspect_i(VALUE key, VALUE value, VALUE str)
 {
     VALUE str2;
 
-    str2 = rb_inspect(key);
+    bool is_symbol = SYMBOL_P(key);
+    bool quote = false;
+    if (is_symbol) {
+        str2 = rb_sym2str(key);
+        quote = symbol_key_needs_quote(str2);
+    }
+    else {
+        str2 = rb_inspect(key);
+    }
     if (RSTRING_LEN(str) > 1) {
         rb_str_buf_cat_ascii(str, ", ");
     }
     else {
         rb_enc_copy(str, str2);
     }
-    rb_str_buf_append(str, str2);
-    rb_str_buf_cat_ascii(str, "=>");
+    if (quote) {
+        rb_str_buf_append(str, rb_str_inspect(str2));
+    }
+    else {
+        rb_str_buf_append(str, str2);
+    }
+
+    rb_str_buf_cat_ascii(str, is_symbol ? ": " : " => ");
     str2 = rb_inspect(value);
     rb_str_buf_append(str, str2);
 

test/ruby/test_hash.rb

@@ -869,6 +869,33 @@ class TestHash < Test::Unit::TestCase
     $, = nil
   end
 
+  def test_inspect
+    no_quote = '{a: 1, a!: 1, a?: 1}'
+    quote0 = '{"": 1}'
+    quote1 = '{"0": 1, "!": 1, "%": 1, "&": 1, "*": 1, "+": 1, "-": 1, "/": 1, "<": 1, ">": 1, "^": 1, "`": 1, "|": 1, "~": 1}'
+    quote2 = '{"@a": 1, "$a": 1, "+@": 1, "a=": 1, "[]": 1}'
+    quote3 = '{"a\"b": 1, "@@a": 1, "<=>": 1, "===": 1, "[]=": 1}'
+    assert_equal(no_quote, eval(no_quote).inspect)
+    assert_equal(quote0, eval(quote0).inspect)
+    assert_equal(quote1, eval(quote1).inspect)
+    assert_equal(quote2, eval(quote2).inspect)
+    assert_equal(quote3, eval(quote3).inspect)
+    begin
+      enc = Encoding.default_external
+      Encoding.default_external = Encoding::ASCII
+      utf8_ascii_hash = '{"\\u3042": 1}'
+      assert_equal(eval(utf8_ascii_hash).inspect, utf8_ascii_hash)
+      Encoding.default_external = Encoding::UTF_8
+      utf8_hash = "{\u3042: 1}"
+      assert_equal(eval(utf8_hash).inspect, utf8_hash)
+      Encoding.default_external = Encoding::Windows_31J
+      sjis_hash = "{\x87]: 1}".force_encoding('sjis')
+      assert_equal(eval(sjis_hash).inspect, sjis_hash)
+    ensure
+      Encoding.default_external = enc
+    end
+  end
+
   def test_update
     h1 = @cls[ 1 => 2, 2 => 3, 3 => 4 ]
     h2 = @cls[ 2 => 'two', 4 => 'four' ]