Make the spec suite compatible with --enable-frozen-string-literal

Extracted from: ruby/ruby#10235

Ref: https://bugs.ruby-lang.org/issues/20205

Ruby will gradually move towards enabling frozen string literals
by default. Making the ruby spec suite compatible is a good first
step.

Co-authored-by: Benoit Daloze <eregontp@gmail.com>

.github/workflows/ci.yml

@@ -10,6 +10,12 @@ jobs:
       matrix:
         os: [ ubuntu, macos, windows ]
         ruby: [ 3.0.6, 3.1.4, 3.2.2, 3.3.0 ]
+        rubyopt: [""]
+        include:
+          - os: ubuntu
+            ruby: 3.3.0
+            rubyopt: "--enable-frozen-string-literal"
+
     runs-on: ${{ matrix.os }}-latest
     steps:
     - name: git config autocrlf
@@ -28,6 +34,7 @@ jobs:
       if: matrix.os == 'ubuntu'
       env:
         CHECK_LEAKS: true
+        RUBYOPT: "${{ matrix.rubyopt }}"
       run: ../mspec/bin/mspec -j --timeout 30
 
     - name: Run specs (macOS)

core/argf/readpartial_spec.rb

@@ -29,7 +29,7 @@
 
   it "clears output buffer even if EOFError is raised because @argf is at end" do
     begin
-      output = "to be cleared"
+      output = +"to be cleared"
 
       argf [@file1_name] do
         @argf.read

core/argf/shared/getc.rb

@@ -9,7 +9,7 @@
 
   it "reads each char of files" do
     argf [@file1, @file2] do
-      chars = ""
+      chars = +""
       @chars.size.times { chars << @argf.send(@method) }
       chars.should == @chars
     end

core/argf/shared/read.rb

@@ -15,15 +15,15 @@
 
   it "treats second argument as an output buffer" do
     argf [@file1_name] do
-      buffer = ""
+      buffer = +""
       @argf.send(@method, @file1.size, buffer)
       buffer.should == @file1
     end
   end
 
   it "clears output buffer before appending to it" do
     argf [@file1_name] do
-      buffer = "to be cleared"
+      buffer = +"to be cleared"
       @argf.send(@method, @file1.size, buffer)
       buffer.should == @file1
     end

core/array/fill_spec.rb

@@ -21,7 +21,7 @@
 
   it "does not replicate the filler" do
     ary = [1, 2, 3, 4]
-    str = "x"
+    str = +"x"
     ary.fill(str).should == [str, str, str, str]
     str << "y"
     ary.should == [str, str, str, str]

core/array/fixtures/encoded_strings.rb

@@ -2,36 +2,36 @@
 module ArraySpecs
   def self.array_with_usascii_and_7bit_utf8_strings
     [
-      'foo'.force_encoding('US-ASCII'),
+      'foo'.dup.force_encoding('US-ASCII'),
       'bar'
     ]
   end
 
   def self.array_with_usascii_and_utf8_strings
     [
-      'foo'.force_encoding('US-ASCII'),
+      'foo'.dup.force_encoding('US-ASCII'),
       'báz'
     ]
   end
 
   def self.array_with_7bit_utf8_and_usascii_strings
     [
       'bar',
-      'foo'.force_encoding('US-ASCII')
+      'foo'.dup.force_encoding('US-ASCII')
     ]
   end
 
   def self.array_with_utf8_and_usascii_strings
     [
       'báz',
       'bar',
-      'foo'.force_encoding('US-ASCII')
+      'foo'.dup.force_encoding('US-ASCII')
     ]
   end
 
   def self.array_with_usascii_and_utf8_strings
     [
-      'foo'.force_encoding('US-ASCII'),
+      'foo'.dup.force_encoding('US-ASCII'),
       'bar',
       'báz'
     ]
@@ -41,7 +41,7 @@ def self.array_with_utf8_and_7bit_binary_strings
     [
       'bar',
       'báz',
-      'foo'.force_encoding('BINARY')
+      'foo'.dup.force_encoding('BINARY')
     ]
   end
 
@@ -55,14 +55,14 @@ def self.array_with_utf8_and_binary_strings
 
   def self.array_with_usascii_and_7bit_binary_strings
     [
-      'bar'.force_encoding('US-ASCII'),
-      'foo'.force_encoding('BINARY')
+      'bar'.dup.force_encoding('US-ASCII'),
+      'foo'.dup.force_encoding('BINARY')
     ]
   end
 
   def self.array_with_usascii_and_binary_strings
     [
-      'bar'.force_encoding('US-ASCII'),
+      'bar'.dup.force_encoding('US-ASCII'),
       [255].pack('C').force_encoding('BINARY')
     ]
   end

core/array/pack/buffer_spec.rb

@@ -13,13 +13,13 @@
   it "adds result at the end of buffer content" do
     n = [ 65, 66, 67 ] # result without buffer is "ABC"
 
-    buffer = ""
+    buffer = +""
     n.pack("ccc", buffer: buffer).should == "ABC"
 
-    buffer = "123"
+    buffer = +"123"
     n.pack("ccc", buffer: buffer).should == "123ABC"
 
-    buffer = "12345"
+    buffer = +"12345"
     n.pack("ccc", buffer: buffer).should == "12345ABC"
   end
 
@@ -31,19 +31,19 @@
   context "offset (@) is specified" do
     it 'keeps buffer content if it is longer than offset' do
       n = [ 65, 66, 67 ]
-      buffer = "123456"
+      buffer = +"123456"
       n.pack("@3ccc", buffer: buffer).should == "123ABC"
     end
 
     it "fills the gap with \\0 if buffer content is shorter than offset" do
       n = [ 65, 66, 67 ]
-      buffer = "123"
+      buffer = +"123"
       n.pack("@6ccc", buffer: buffer).should == "123\0\0\0ABC"
     end
 
     it 'does not keep buffer content if it is longer than offset + result' do
       n = [ 65, 66, 67 ]
-      buffer = "1234567890"
+      buffer = +"1234567890"
       n.pack("@3ccc", buffer: buffer).should == "123ABC"
     end
   end

core/array/pack/shared/string.rb

@@ -40,7 +40,7 @@
     f = pack_format("*")
     [ [["\u{3042 3044 3046 3048}", 0x2000B].pack(f+"U"),       Encoding::BINARY],
       [["abcde\xd1", "\xFF\xFe\x81\x82"].pack(f+"u"),          Encoding::BINARY],
-      [["a".force_encoding("ascii"), "\xFF\xFe\x81\x82"].pack(f+"u"), Encoding::BINARY],
+      [["a".dup.force_encoding("ascii"), "\xFF\xFe\x81\x82"].pack(f+"u"), Encoding::BINARY],
       # under discussion [ruby-dev:37294]
       [["\u{3042 3044 3046 3048}", 1].pack(f+"N"),             Encoding::BINARY]
     ].should be_computed_by(:encoding)

core/array/shared/inspect.rb

@@ -19,7 +19,7 @@
   end
 
   it "does not call #to_s on a String returned from #inspect" do
-    str = "abc"
+    str = +"abc"
     str.should_not_receive(:to_s)
 
     [str].send(@method).should == '["abc"]'
@@ -98,8 +98,8 @@
     end
 
     it "does not raise if inspected result is not default external encoding" do
-      utf_16be = mock("utf_16be")
-      utf_16be.should_receive(:inspect).and_return(%<"utf_16be \u3042">.encode!(Encoding::UTF_16BE))
+      utf_16be = mock(+"utf_16be")
+      utf_16be.should_receive(:inspect).and_return(%<"utf_16be \u3042">.encode(Encoding::UTF_16BE))
 
       [utf_16be].send(@method).should == '["utf_16be \u3042"]'
     end

core/complex/inspect_spec.rb

@@ -17,7 +17,8 @@
 
   it "calls #inspect on real and imaginary" do
     real = NumericSpecs::Subclass.new
-    real.should_receive(:inspect).and_return("1")
+    # + because of https://bugs.ruby-lang.org/issues/20337
+    real.should_receive(:inspect).and_return(+"1")
     imaginary = NumericSpecs::Subclass.new
     imaginary.should_receive(:inspect).and_return("2")
     imaginary.should_receive(:<).any_number_of_times.and_return(false)
@@ -26,7 +27,8 @@
 
   it "adds an `*' before the `i' if the last character of the imaginary part is not numeric" do
     real = NumericSpecs::Subclass.new
-    real.should_receive(:inspect).and_return("(1)")
+    # + because of https://bugs.ruby-lang.org/issues/20337
+    real.should_receive(:inspect).and_return(+"(1)")
     imaginary = NumericSpecs::Subclass.new
     imaginary.should_receive(:inspect).and_return("(2)")
     imaginary.should_receive(:<).any_number_of_times.and_return(false)

core/complex/to_s_spec.rb

@@ -45,7 +45,8 @@
 
   it "treats real and imaginary parts as strings" do
     real = NumericSpecs::Subclass.new
-    real.should_receive(:to_s).and_return("1")
+    # + because of https://bugs.ruby-lang.org/issues/20337
+    real.should_receive(:to_s).and_return(+"1")
     imaginary = NumericSpecs::Subclass.new
     imaginary.should_receive(:to_s).and_return("2")
     imaginary.should_receive(:<).any_number_of_times.and_return(false)

core/dir/children_spec.rb

@@ -47,7 +47,7 @@
     encoding = Encoding.find("filesystem")
     encoding = Encoding::BINARY if encoding == Encoding::US_ASCII
     platform_is_not :windows do
-      children.should include("こんにちは.txt".force_encoding(encoding))
+      children.should include("こんにちは.txt".dup.force_encoding(encoding))
     end
     children.first.encoding.should equal(Encoding.find("filesystem"))
   end
@@ -113,7 +113,7 @@
     encoding = Encoding.find("filesystem")
     encoding = Encoding::BINARY if encoding == Encoding::US_ASCII
     platform_is_not :windows do
-      children.should include("こんにちは.txt".force_encoding(encoding))
+      children.should include("こんにちは.txt".dup.force_encoding(encoding))
     end
     children.first.encoding.should equal(Encoding.find("filesystem"))
   end

core/dir/entries_spec.rb

@@ -47,7 +47,7 @@
     encoding = Encoding.find("filesystem")
     encoding = Encoding::BINARY if encoding == Encoding::US_ASCII
     platform_is_not :windows do
-      entries.should include("こんにちは.txt".force_encoding(encoding))
+      entries.should include("こんにちは.txt".dup.force_encoding(encoding))
     end
     entries.first.encoding.should equal(Encoding.find("filesystem"))
   end

core/dir/shared/glob.rb

@@ -12,7 +12,7 @@
   end
 
   it "raises an Encoding::CompatibilityError if the argument encoding is not compatible with US-ASCII" do
-    pattern = "file*".force_encoding Encoding::UTF_16BE
+    pattern = "file*".dup.force_encoding Encoding::UTF_16BE
     -> { Dir.send(@method, pattern) }.should raise_error(Encoding::CompatibilityError)
   end