Fix Regex#inspect with non-literal-compatible options (#14575)

spec/std/regex_spec.cr

@@ -449,15 +449,29 @@ describe "Regex" do
   end
 
   describe "#inspect" do
-    it "with options" do
-      /foo/.inspect.should eq("/foo/")
-      /foo/im.inspect.should eq("/foo/im")
-      /foo/imx.inspect.should eq("/foo/imx")
+    context "with literal-compatible options" do
+      it "prints flags" do
+        /foo/.inspect.should eq("/foo/")
+        /foo/im.inspect.should eq("/foo/im")
+        /foo/imx.inspect.should eq("/foo/imx")
+      end
+
+      it "escapes" do
+        %r(/).inspect.should eq("/\\//")
+        %r(\/).inspect.should eq("/\\//")
+      end
     end
 
-    it "escapes" do
-      %r(/).inspect.should eq("/\\//")
-      %r(\/).inspect.should eq("/\\//")
+    context "with non-literal-compatible options" do
+      it "prints flags" do
+        Regex.new("foo", :anchored).inspect.should eq %(Regex.new("foo", Regex::Options::ANCHORED))
+        Regex.new("foo", :no_utf_check).inspect.should eq %(Regex.new("foo", Regex::Options::NO_UTF8_CHECK))
+        Regex.new("foo", Regex::CompileOptions[IGNORE_CASE, ANCHORED]).inspect.should eq %(Regex.new("foo", Regex::Options[IGNORE_CASE, ANCHORED]))
+      end
+
+      it "escapes" do
+        Regex.new(%("), :anchored).inspect.should eq %(Regex.new("\\"", Regex::Options::ANCHORED))
+      end
     end
   end
 

src/regex.cr

@@ -590,14 +590,36 @@ class Regex
     nil
   end
 
-  # Convert to `String` in literal format. Returns the source as a `String` in
-  # Regex literal format, delimited in forward slashes (`/`), with any
-  # optional flags included.
+  # Prints to *io* an unambiguous string representation of this regular expression object.
   #
+  # Uses the regex literal syntax with basic option flags if sufficient (i.e. no
+  # other options than `IGNORE_CASE`, `MULTILINE`, or `EXTENDED` are set).
+  # Otherwise the syntax presents a `Regex.new` call.
   # ```
-  # /ab+c/ix.inspect # => "/ab+c/ix"
+  # /ab+c/ix.inspect                     # => "/ab+c/ix"
+  # Regex.new("ab+c", :anchored).inspect # => Regex.new("ab+c", Regex::Options::ANCHORED)
   # ```
   def inspect(io : IO) : Nil
+    if (options & ~CompileOptions[IGNORE_CASE, MULTILINE, EXTENDED]).none?
+      inspect_literal(io)
+    else
+      inspect_extensive(io)
+    end
+  end
+
+  # Convert to `String` in literal format. Returns the source as a `String` in
+  # Regex literal format, delimited in forward slashes (`/`), with option flags
+  # included.
+  #
+  # Only `IGNORE_CASE`, `MULTILINE`, and `EXTENDED` options can be represented.
+  # Any other option value is ignored. Use `#inspect` instead for an unambiguous
+  # and correct representation.
+  #
+  # ```
+  # /ab+c/ix.inspect_literal                     # => "/ab+c/ix"
+  # Regex.new("ab+c", :anchored).inspect_literal # => "/ab+c/"
+  # ```
+  private def inspect_literal(io : IO) : Nil
     io << '/'
     Regex.append_source(source, io)
     io << '/'
@@ -606,6 +628,22 @@ class Regex
     io << 'x' if options.extended?
   end
 
+  # Prints to *io* an extensive string representation of this regular expression object.
+  # The result is unambiguous and mirrors a Crystal expression to recreate an equivalent
+  # instance.
+  #
+  # ```
+  # /ab+c/ix.inspect_literal                     # => Regex.new("ab+c", Regex::Options[IGNORE_CASE, EXTENDED])
+  # Regex.new("ab+c", :anchored).inspect_literal # => Regex.new("ab+c", Regex::Options::ANCHORED)
+  # ```
+  private def inspect_extensive(io : IO) : Nil
+    io << "Regex.new("
+    source.inspect(io)
+    io << ", "
+    options.inspect(io)
+    io << ")"
+  end
+
   # Match at character index. Matches a regular expression against `String`
   # *str*. Starts at the character index given by *pos* if given, otherwise at
   # the start of *str*. Returns a `Regex::MatchData` if *str* matched, otherwise