1 files changed, 50 insertions, 0 deletions
diff --git a/spec/ruby/language/regexp/subexpression_call_spec.rb b/spec/ruby/language/regexp/subexpression_call_spec.rb
new file mode 100644
index 0000000000..16b64cb327
--- /dev/null
+++ b/spec/ruby/language/regexp/subexpression_call_spec.rb
@@ -0,0 +1,50 @@
+require_relative '../../spec_helper'
+require_relative '../fixtures/classes'
+
+describe "Regexps with subexpression calls" do
+  it "allows numeric subexpression calls" do
+    /(a)\g<1>/.match("aa").to_a.should == [ "aa", "a" ]
+  end
+
+  it "treats subexpression calls as distinct from simple back-references" do
+    # Back-references only match a string which is equal to the original captured string.
+    /(?<three_digits>[0-9]{3})-\k<three_digits>/.match("123-123")[0].should == "123-123"
+    /(?<three_digits>[0-9]{3})-\k<three_digits>/.match("123-456").should == nil
+    # However, subexpression calls reuse the previous expression and can match a different
+    # string.
+    /(?<three_digits>[0-9]{3})-\g<three_digits>/.match("123-456")[0].should == "123-456"
+  end
+
+  it "allows recursive subexpression calls" do
+    # This pattern matches well-nested parenthesized expression.
+    parens = /^ (?<parens>  (?: \( \g<parens> \) | [^()] )*  ) $/x
+    parens.match("((a)(b))c(d)")[0].should == "((a)(b))c(d)"
+    parens.match("((a)(b)c(d)").should == nil
+  end
+
+  it "allows access to back-references from the current level" do
+    # Using \\k<first_char-0> accesses the last value captured in first_char
+    # on the current stack level.
+    mirror = /^ (?<mirror> (?: (?<first_char>.) \g<mirror> \k<first_char-0> )? ) $/x
+    mirror.match("abccba")[0].should == "abccba"
+    mirror.match("abccbd").should == nil
+
+    # OTOH, using \\k<first_char> accesses the last value captured in first_char,
+    # regardless of the stack level. Therefore, it can't be used to implement
+    # the mirror language.
+    broken_mirror = /^ (?<mirror> (?: (?<first_char>.) \g<mirror> \k<first_char> )? ) $/x
+    broken_mirror.match("abccba").should == nil
+    # This matches because the 'c' is captured in first_char and that value is
+    # then used for all subsequent back-references, regardless of nesting.
+    broken_mirror.match("abcccc")[0].should == "abcccc"
+  end
+
+  it "allows + and - in group names and referential constructs that don't use levels, i.e. subexpression calls" do
+    /(?<a+>a)\g<a+>/.match("aa").to_a.should == [ "aa", "a" ]
+    /(?<a+b>a)\g<a+b>/.match("aa").to_a.should == [ "aa", "a" ]
+    /(?<a+1>a)\g<a+1>/.match("aa").to_a.should == [ "aa", "a" ]
+    /(?<a->a)\g<a->/.match("aa").to_a.should == [ "aa", "a" ]
+    /(?<a-b>a)\g<a-b>/.match("aa").to_a.should == [ "aa", "a" ]
+    /(?<a-1>a)\g<a-1>/.match("aa").to_a.should == [ "aa", "a" ]
+  end
+end