Add brace expansion

ruby/shell/word_expander.rb

@@ -18,11 +18,19 @@ module Shell
       protected_line = protect_escaped_dollars(line)
       substituted_line = expand_command_substitution(protected_line)
       shellsplit(substituted_line)
-        .map do |word|
+        .flat_map do |word|
-          expand_variables(word)
+          expanded = expand_variables(word)
             .tr(ESCAPED_DOLLAR, "$")
             .tr(ESCAPED_BACKTICK, "`")
-          # TODO: expand globs
+          expand_braces(expanded)
+        end
+        .flat_map do |word|
+          if word =~ /[*?\[]/
+            glob_words = expand_globs(word)
+            glob_words.empty? ? [word] : glob_words
+          else
+            [word]
+          end
         end
     end
 
@@ -268,6 +276,20 @@ module Shell
       stdout.tr("\n", " ")
     end
 
+    def expand_braces(word)
+      # Simple, non-nested brace expansion: pre{a,b}post -> preapost, prebpost
+      match = word.match(/(.*?)\{([^{}]*)\}(.*)/)
+      return [word] unless match
+
+      prefix = match[1]
+      body = match[2]
+      suffix = match[3]
+      return [word] unless body.include?(",")
+
+      parts = body.split(",", -1)
+      parts.flat_map { |part| expand_braces(prefix + part + suffix) }
+    end
+
     def escaped_replacement(char)
       case char
       when "$"

ruby/test/shell_test.rb

@@ -63,7 +63,6 @@ class ShellTest < Minitest::Test
   end
 
   def test_expands_brace_expansion
-    skip "brace expansion not implemented"
     assert_equal "a b", `#{A1_PATH} -c 'echo {a,b}'`.chomp
   end
 
@@ -99,7 +98,7 @@ class ShellTest < Minitest::Test
   end
 
   def test_does_not_expand_escaped_command_substitution_dollar_paren_in_double_quotes
-    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