Incompatibilities with --enable-frozen-string-literal

[strayer]

Slim has various issues with frozen string literals. Some are pretty easy to fix:

diff --git a/lib/slim/embedded.rb b/lib/slim/embedded.rb
index 316809c..adb6e57 100644
--- a/lib/slim/embedded.rb
+++ b/lib/slim/embedded.rb
@@ -8,7 +8,7 @@ module Slim
     end
 
     def on_slim_interpolate(text)
-      @collected << text
+      @collected += text
       nil
     end
   end
@@ -36,12 +36,12 @@ module Slim
     end
 
     def on_static(text)
-      @collected << text
+      @collected += text
       nil
     end
 
     def on_slim_output(escape, text, content)
-      @collected << @tag
+      @collected += @tag
       @protect << [:slim, :output, escape, text, content]
       nil
     end
diff --git a/lib/slim/parser.rb b/lib/slim/parser.rb
index 810779c..6f68cd4 100644
--- a/lib/slim/parser.rb
+++ b/lib/slim/parser.rb
@@ -84,7 +84,7 @@ module Slim
       @code_attr_re = /#{@attr_name}\s*=(=?)\s*/
 
       splat_prefix = Regexp.escape(options[:splat_prefix])
-      splat_regexp_source = '\A\s*' << splat_prefix << '(?=[^\s]+)'
+      splat_regexp_source = '\A\s*' + splat_prefix + '(?=[^\s]+)'
       @splat_attrs_regexp = Regexp.new(splat_regexp_source)
     end
 
@@ -478,7 +478,7 @@ module Slim
 
       until @line.empty? || (count == 0 && @line =~ end_re)
         if @line =~ /\A[,\\]\Z/
-          code << @line << "\n"
+          code += @line + "\n"
           expect_next_line
         else
           if count > 0
@@ -491,7 +491,7 @@ module Slim
             count = 1
             delimiter, close_delimiter = $&, @code_attr_delims[$&]
           end
-          code << @line.slice!(0)
+          code += @line.slice!(0)
         end
       end
       syntax_error!("Expected closing delimiter #{close_delimiter}") if count != 0
@@ -503,7 +503,7 @@ module Slim
 
       until count == 0 && @line[0] == quote[0]
         if @line =~ /\A(\\)?\Z/
-          value << ($1 ? ' ' : "\n")
+          value += ($1 ? ' ' : "\n")
           expect_next_line
         else
           if @line[0] == ?{
@@ -511,7 +511,7 @@ module Slim
           elsif @line[0] == ?}
             count -= 1
           end
-          value << @line.slice!(0)
+          value += @line.slice!(0)
         end
       end
 
diff --git a/test/core/test_encoding.rb b/test/core/test_encoding.rb
index b69ce5f..14fc99c 100644
--- a/test/core/test_encoding.rb
+++ b/test/core/test_encoding.rb
@@ -9,13 +9,13 @@ class TestSlimEncoding < TestSlim
 
   def test_binary
     source = "| \xFF\xFF"
-    source.force_encoding(Encoding::BINARY)
+    source = source.dup.force_encoding(Encoding::BINARY)
 
     result = "\xFF\xFF"
-    result.force_encoding(Encoding::BINARY)
+    result = result.dup.force_encoding(Encoding::BINARY)
 
     out = render(source, default_encoding: 'binary')
-    out.force_encoding(Encoding::BINARY)
+    out = out.dup.force_encoding(Encoding::BINARY)
 
     assert_equal result, out
   end

Note: there are possible performance improvements with using "".dup instead of +=, see Friendly Frozen String Literals for reference. Just wanted to start working on this issue and see quick results.

But then some cryptic issues happen within tilt, which I couldn't yet figure out:

254) Error:
TestSlimCodeEvaluation#test_render_with_call_to_set_custom_attributes:
FrozenError: can't modify frozen String: ""
    (__TEMPLATE__):2:in `__tilt_1880'
    /Users/strayer/.asdf/installs/ruby/2.7.0/lib/ruby/gems/2.7.0/gems/tilt-2.0.10/lib/tilt/template.rb:170:in `call'
    /Users/strayer/.asdf/installs/ruby/2.7.0/lib/ruby/gems/2.7.0/gems/tilt-2.0.10/lib/tilt/template.rb:170:in `evaluate'
    /Users/strayer/.asdf/installs/ruby/2.7.0/lib/ruby/gems/2.7.0/gems/tilt-2.0.10/lib/tilt/template.rb:109:in `render'
    /Users/strayer/.../slim/test/core/helper.rb:22:in `render'
    /Users/strayer/.../slim/test/core/helper.rb:45:in `assert_html'
    /Users/strayer/.../slim/test/core/test_code_evaluation.rb:18:in `test_render_with_call_to_set_custom_attributes'

Any idea how to tackle this? I'd love to investigate this further and provide a PR, but I am really at a loss what happens here.

[tainoe]

The error in that test is caused by Temple, not Slim.
Temple should be fixed like this:

diff --git a/lib/temple/generators/string_buffer.rb b/lib/temple/generators/string_buffer.rb
index c22646c..673a991 100644
--- a/lib/temple/generators/string_buffer.rb
+++ b/lib/temple/generators/string_buffer.rb
@@ -10,7 +10,7 @@ module Temple
     # @api public
     class StringBuffer < ArrayBuffer
       def create_buffer
-        "#{buffer} = ''"
+        "#{buffer} = ''.dup"
       end

       def return_buffer

And codes you suggested did not work even in no --enable-frozen-string-literal environment.
Fixing variable initialization is more compatible like this:

diff --git a/lib/slim/embedded.rb b/lib/slim/embedded.rb
index 316809c..9dd7ec3 100644
--- a/lib/slim/embedded.rb
+++ b/lib/slim/embedded.rb
@@ -2,7 +2,7 @@ module Slim
   # @api private
   class TextCollector < Filter
     def call(exp)
-      @collected = ''
+      @collected = ''.dup
       super(exp)
       @collected
     end
@@ -30,7 +30,7 @@ module Slim
   # @api private
   class OutputProtector < Filter
     def call(exp)
-      @protect, @collected, @tag = [], '', "%#{object_id.abs.to_s(36)}%"
+      @protect, @collected, @tag = [], ''.dup, "%#{object_id.abs.to_s(36)}%"
       super(exp)
       @collected
     end
diff --git a/lib/slim/parser.rb b/lib/slim/parser.rb
index 810779c..3c449dc 100644
--- a/lib/slim/parser.rb
+++ b/lib/slim/parser.rb
@@ -84,7 +84,7 @@ module Slim
       @code_attr_re = /#{@attr_name}\s*=(=?)\s*/

       splat_prefix = Regexp.escape(options[:splat_prefix])
-      splat_regexp_source = '\A\s*' << splat_prefix << '(?=[^\s]+)'
+      splat_regexp_source = '\A\s*' + splat_prefix + '(?=[^\s]+)'
       @splat_attrs_regexp = Regexp.new(splat_regexp_source)
     end

@@ -471,7 +471,7 @@ module Slim
     end

     def parse_ruby_code(outer_delimiter)
-      code, count, delimiter, close_delimiter = '', 0, nil, nil
+      code, count, delimiter, close_delimiter = ''.dup, 0, nil, nil

       # Attribute ends with space or attribute delimiter
       end_re = /\A[\s#{Regexp.escape outer_delimiter.to_s}]/
@@ -499,7 +499,7 @@ module Slim
     end

     def parse_quoted_attribute(quote)
-      value, count = '', 0
+      value, count = ''.dup, 0

       until count == 0 && @line[0] == quote[0]
         if @line =~ /\A(\\)?\Z/

[minad]

If I understood correctly Ruby is moving to frozen literals by default? We should make this change slowly by adding frozen_string_literal headers to every file in Slim and Temple. PRs welcome!

[minad]

Implemented in Temple and Slim. See e1b66cc and judofyr/temple@0173e5e. Please confirm that it works for you.