Respect escaped command substitution

ruby/shell/repl.rb

@@ -113,12 +113,7 @@ module Shell
           state = :unquoted if c == "\""
 
         when :double_quoted_escape
-          case c
+          command << "\\"
-          when "\"", "\\", "$", "`"
-            # no-op
-          else
-            command << "\\" # POSIX behaviour, backslash remains
-          end
           command << c
           state = :double_quoted
 

ruby/shell/word_expander.rb

@@ -6,6 +6,7 @@ module Shell
     ENV_VAR_REGEX = /\$(?:\{([^}]+)\}|(\w+)\b)/
     DEFAULT_VAR_REGEX = /\A(\w+):-([\s\S]*)\z/
     ESCAPED_DOLLAR = "\u0001"
+    ESCAPED_BACKTICK = "\u0002"
 
     # Splits the given line into multiple words, performing the following transformations:
     #
@@ -18,7 +19,9 @@ module Shell
       substituted_line = expand_command_substitution(protected_line)
       shellsplit(substituted_line)
         .map do |word|
-          expand_variables(word).tr(ESCAPED_DOLLAR, "$")
+          expand_variables(word)
+            .tr(ESCAPED_DOLLAR, "$")
+            .tr(ESCAPED_BACKTICK, "`")
           # TODO: expand globs
         end
     end
@@ -138,6 +141,23 @@ module Shell
               output << c
               i += 1
             end
+          when "\\"
+            if i + 1 < line.length
+              escaped = line[i + 1]
+              if escaped == "$"
+                output << ESCAPED_DOLLAR
+                i += 2
+              elsif escaped == "`"
+                output << ESCAPED_BACKTICK
+                i += 2
+              else
+                output << c
+                i += 1
+              end
+            else
+              output << c
+              i += 1
+            end
           else
             output << c
             i += 1
@@ -154,6 +174,20 @@ module Shell
             output << c
             state = :unquoted
             i += 1
+          when "\\"
+            if i + 1 < line.length
+              escaped = line[i + 1]
+              if escaped == "$" || escaped == "`" || escaped == "\\" || escaped == "\""
+                output << (escaped == "$" ? ESCAPED_DOLLAR : (escaped == "`" ? ESCAPED_BACKTICK : escaped))
+              else
+                output << "\\"
+                output << escaped
+              end
+              i += 2
+            else
+              output << c
+              i += 1
+            end
           when "`"
             cmd, i = read_backtick(line, i + 1)
             output << run_command_substitution(cmd)
@@ -263,5 +297,6 @@ module Shell
       end
       output
     end
+
   end
 end

ruby/test/shell_test.rb

@@ -99,13 +99,11 @@ class ShellTest < Minitest::Test
   end
 
   def test_does_not_expand_escaped_command_substitution_dollar_paren_in_double_quotes
-    skip "escape handling for command substitution in double quotes is limited"
+    assert_equal "$(echo hi)", %x(#{A1_PATH} -c 'echo "\\$(echo hi)"').chomp
-    assert_equal "$(echo hi)", `#{A1_PATH} -c 'echo "\\$(echo hi)"'`.chomp
   end
 
   def test_does_not_expand_escaped_command_substitution_backticks_in_double_quotes
-    skip "escape handling for command substitution in double quotes is limited"
+    assert_equal "`echo hi`", %x(#{A1_PATH} -c 'echo "\\`echo hi\\`"').chomp
-    assert_equal "`echo hi`", %x(#{A1_PATH} -c "echo \"\\`echo hi\\`\"").chomp
   end
 
   #################################