Slightly rewrite Oniguruma indentation rules

Author: FichteFoll

Package/Sublime Text Syntax Definition/Oniguruma RegExp Indentation Rules.tmPreferences

@@ -8,68 +8,64 @@
     <dict>
         <key>comment</key>
         <string>
-            Indent any unclosed groups - open  parens that don't have a corresponding closing paren on the same line.
-            Unindent any closed groups - close parens that don't have a corresponding opening paren on the same line.
-            Also apply to the `expect-regexp` meta scope, because otherwise a line like `- match: (?=\))` in a `.sublime-syntax` file would not have these rules applied to it because the `source.regexp` scope (correctly) doesn't cover the newline.
+            Indent any unclosed groups
+            (open paren that doesn't have a corresponding closing paren on the same line).
+
+            Unindent when a closing paren is the first non-whitespace character on a line.
+
+            Also apply to the `expect-regexp` meta scope,
+            because otherwise a line like `- match: (?=\))` in a `.sublime-syntax` file
+            would not have these rules applied to it
+            because the `source.regexp` scope (correctly) doesn't cover the newline.
+
             Parens inside comments (whether YAML or Regex) are ignored.
         </string>
         <key>indentParens</key>
         <false/>
         <key>increaseIndentPattern</key>
-        <string><![CDATA[(?x)^
+        <string><![CDATA[(?x)
+            # define sub-expressions
             (?<not_paren>
-                (?:
-                    [^\\()]++              # anything that isn't a slash or a paren
-                |   \\(?>                  # this is the "known_char_escape" variable from the syntax definition
-                        [tnrfae]
-                    |   [0-7]{3}
-                    |   x \h\h
-                    |   x \{ \h{1,8} \}
-                    |   c \d+
-                    |   C- \d+
-                    |   M- \d+
-                    |   M-\\C- \d+
-                    )
-                |   \\.                    # a single escape character
+                [^\\()]++              # anything that isn't a slash or a paren
+            |   \\(?>                  # this is the "known_char_escape" variable from the syntax definition
+                    [tnrfae]
+                |   [0-7]{3}
+                |   x \h\h
+                |   x \{ \h{1,8} \}
+                |   c \d+
+                |   C- \d+
+                |   M- \d+
+                |   M-\\C- \d+
+                )
+            |   \\.                    # a single escape character
+            ){0}
+            (?<group>
+                \(                     # an open paren
+                (                      # followed by either
+                    \g<not_paren>      # ... anything that's not a group-related paren
+                |   \g<group> # ... or a parens group (recursive)
                 )*+
-            )
-            (?<balanced_paren>(?:
-                \(                         # an open paren
-                \g<not_paren>              # followed by anything that's not a group-related paren
-                \g<balanced_paren>         # followed by any number of nested parens
-                \g<not_paren>              # followed by anything that's not a group-related paren
-                \)                         # a closing paren
-            )*+)
-            \g<not_paren>                  # followed by anything that's not a group-related paren
-            \(                             # followed by an unbalanced open paren
+                \)                     # a closing paren
+            ){0}
+            (?<balanced_pattern>
+                (
+                    \g<not_paren>      # anything that's not a group-related paren
+                |   \g<group>          # or a parens group (recursive)
+                )*+
+            ){0}
+
+            # now the actual match
+            ^                      # start at the beginning of the line
+            \g<balanced_pattern>   # the longest sequence of groups and non-group characters
+            \(                     # followed by an unbalanced open paren
         ]]></string>
         <key>decreaseIndentPattern</key>
-        <string><![CDATA[(?x)^
-            (?<not_paren>
-                (?:
-                    [^\\()]++              # anything that isn't a slash or a paren
-                |   \\(?>                  # this is the "known_char_escape" variable from the syntax definition
-                        [tnrfae]
-                    |   [0-7]{3}
-                    |   x \h\h
-                    |   x \{ \h{1,8} \}
-                    |   c \d+
-                    |   C- \d+
-                    |   M- \d+
-                    |   M-\\C- \d+
-                    )
-                |   \\.                    # a single escape character
-                )*+
-            )
-            (?<balanced_paren>(?:
-                \(                         # an open paren
-                \g<not_paren>              # followed by anything that's not a group-related paren
-                \g<balanced_paren>         # followed by any number of nested parens
-                \g<not_paren>              # followed by anything that's not a group-related paren
-                \)                         # a closing paren
-            )*+)
-            \g<not_paren>                  # followed by anything that's not a group-related paren
-            \)                             # followed by an unbalanced close paren
+        <string><![CDATA[(?x)
+            # decrease indentation (while typing)
+            # if a closing paren is the first non-whitespace character on a line
+            ^
+            \s*
+            \)
         ]]></string>
     </dict>
 </dict>