[GR-18163] Fix StringIO#initialize and preserve initial string's encoding

PullRequest: truffleruby/4306

Author: andrykonchin

CHANGELOG.md

@@ -34,6 +34,7 @@ Compatibility:
 * Fix `RangeError` message to match CRuby for `Integer#chr` called with invalid codepoint argument (#2795, @andrykonchin).
 * Joni has been updated from 2.1.44 to 2.2.1 (@andrykonchin).
 * Fix `Hash#to_h` called with a block and pass key and value to the block as separate arguments (#3607, @andrykonchin).
+* Fix `StringIO#initialize` and preserve initial string's encoding when mode is `w` so the initial string is truncated (#3599, @andrykonchin).
 
 Performance:
 

lib/truffle/stringio.rb

@@ -166,6 +166,14 @@ def initialize(string = nil, mode = nil, **options)
       mode_from_string(string.frozen? ? 'r' : 'r+')
     end
 
+    if @writable && @__data__.string.frozen?
+      raise Errno::EACCES, 'Permission denied'
+    end
+
+    if @truncate
+      @__data__.string.replace(''.force_encoding(@__data__.string.encoding))
+    end
+
     self
   end
 
@@ -672,43 +680,37 @@ def yaml_initialize(type, val)
   end
 
   private def mode_from_string(mode)
-    @append = truncate = false
+    @append = @truncate = false
 
     if mode[0] == ?r
       @readable = true
       @writable = mode[-1] == ?+ ? true : false
     end
 
     if mode[0] == ?w
-      @writable = truncate = true
+      @writable = @truncate = true
       @readable = mode[-1] == ?+ ? true : false
     end
 
     if mode[0] == ?a
       @append = @writable = true
       @readable = mode[-1] == ?+ ? true : false
     end
-
-    d = @__data__ # no sync, only called from initialize
-    raise Errno::EACCES, 'Permission denied' if @writable && d.string.frozen?
-    d.string.replace('') if truncate
   end
 
   private def mode_from_integer(mode)
-    @readable = @writable = @append = false
-    d = @__data__ # no sync, only called from initialize
+    @readable = @writable = @append = @truncate = false
 
     if mode == 0 or mode & IO::RDWR != 0
       @readable = true
     end
 
     if mode & (IO::WRONLY | IO::RDWR) != 0
-      raise Errno::EACCES, 'Permission denied' if d.string.frozen?
       @writable = true
     end
 
     @append = true if (mode & IO::APPEND) != 0
-    d.string.replace('') if (mode & IO::TRUNC) != 0
+    @truncate = true if (mode & IO::TRUNC) != 0
   end
 
   private def getline(arg_error, sep, limit, chomp = false)

spec/ruby/library/stringio/initialize_spec.rb

@@ -130,6 +130,26 @@
     -> { @io.send(:initialize, str, "w") }.should raise_error(Errno::EACCES)
     -> { @io.send(:initialize, str, "a") }.should raise_error(Errno::EACCES)
   end
+
+  it "truncates all the content if passed w mode" do
+    io = StringIO.allocate
+    source = +"example".encode(Encoding::ISO_8859_1);
+
+    io.send(:initialize, source, "w")
+
+    io.string.should.empty?
+    io.string.encoding.should == Encoding::ISO_8859_1
+  end
+
+  it "truncates all the content if passed IO::TRUNC mode" do
+    io = StringIO.allocate
+    source = +"example".encode(Encoding::ISO_8859_1);
+
+    io.send(:initialize, source, IO::TRUNC)
+
+    io.string.should.empty?
+    io.string.encoding.should == Encoding::ISO_8859_1
+  end
 end
 
 describe "StringIO#initialize when passed [Object]" do
@@ -172,7 +192,7 @@
 # NOTE: Synchronise with core/io/new_spec.rb (core/io/shared/new.rb)
 describe "StringIO#initialize when passed keyword arguments" do
   it "sets the mode based on the passed :mode option" do
-    io = StringIO.new("example", "r")
+    io = StringIO.new("example", mode: "r")
     io.closed_read?.should be_false
     io.closed_write?.should be_true
   end