[GR-18163] Accept string pattern for StringScanner headonly searches.

PullRequest: truffleruby/2880

Author: aardvark179

CHANGELOG.md

@@ -34,6 +34,7 @@ Compatibility:
 * Add support for tracing allocations from C functions (#2403, @chrisseaton).
 * Implement `rb_str_catf`.
 * Search the executable in the passed env `PATH` for subprocesses (#2419).
+* Accept a string as the pattern argument to `StringScanner#scan` and `StringScanner#check` (#2423).
 
 Performance:
 

lib/truffle/strscan.rb

@@ -309,7 +309,11 @@ def peep(len)
   end
 
   private def scan_check_args(pattern, headonly)
-    unless pattern.kind_of? Regexp
+    case pattern
+    when String
+      raise TypeError, "bad pattern argument: #{pattern.inspect}" unless headonly
+    when Regexp
+    else
       raise TypeError, "bad pattern argument: #{pattern.inspect}"
     end
     raise ArgumentError, 'uninitialized StringScanner object' unless @string
@@ -321,7 +325,11 @@ def peep(len)
   private def scan_internal(pattern, advance_pos, getstr, headonly)
     scan_check_args(pattern, headonly)
 
-    md = Truffle::RegexpOperations.match_in_region pattern, @string, pos, @string.bytesize, headonly, pos
+    if Primitive.object_kind_of?(pattern, String)
+      md = scan_internal_string_pattern(pattern, headonly)
+    else
+      md = Truffle::RegexpOperations.match_in_region pattern, @string, pos, @string.bytesize, headonly, pos
+    end
     if md
       Primitive.matchdata_fixup_positions(md, pos)
       @match = md
@@ -331,6 +339,14 @@ def peep(len)
     end
   end
 
+  private def scan_internal_string_pattern(pattern, headonly)
+    if @string.byteslice(pos..).start_with?(pattern)
+      Primitive.matchdata_create_single_group(pattern, @string.dup, 0, pattern.bytesize)
+    else
+      nil
+    end
+  end
+
   private def scan_internal_set_pos_and_str(advance_pos, getstr, md)
     fin = Primitive.match_data_byte_end(md, 0)
 

spec/ruby/library/stringscanner/check_spec.rb

@@ -13,4 +13,15 @@
     @s.check(/is/).should == nil
     @s.matched.should == nil
   end
+
+  ruby_version_is "2.7" do
+    it "treats String as the pattern itself" do
+      @s.check("This").should == "This"
+      @s.matched.should == "This"
+      @s.pos.should == 0
+      @s.check(/is/).should == nil
+      @s.matched.should == nil
+    end
+  end
+
 end

spec/tags/library/stringscanner/scan_tags.txt

@@ -1,3 +1,2 @@
-fails:StringScanner#scan treats String as the pattern itself
 fails:StringScanner#scan with fixed_anchor: true treats ^ as matching from the beginning of line
 fails:StringScanner#scan with fixed_anchor: true treats \A as matching from the beginning of string

test/mri/excludes/TestStringScanner.rb

@@ -9,4 +9,3 @@
 exclude :test_matched, "needs investigation"
 exclude :test_post_match, "needs investigation"
 exclude :test_pre_match, "needs investigation"
-exclude :test_scan_string, "needs investigation"