userdiff: extend Scheme support for other Lisp dialects

Common Lisp, Emacs Lisp, and other dialects have some top-level forms,
most importantly 'defun', that are not matched by the current Scheme
pattern.  Also, it is common in these dialects, when defining user
macros intended as top-level forms, to prefix their names with "def"
instead of "define"; such forms are also not currently matched.  Some
such forms don't even begin with "def".

On the other hand, it is an established formatting convention in the
Lisp community that only top-level forms start at the left margin.  So
matching any unindented line starting with an open parenthesis is an
acceptable heuristic; false positives will be rare.

However, there are also cases where notionally top-level forms are
grouped together within some containing form.  At least in the Common
Lisp community, it is conventional to indent these by two spaces, or
sometimes one.  But matching just an open parenthesis indented by two
spaces would be too broad; so the pattern added by this commit
requires an indented form to start with "(def".  It is believed that
this strikes a good balance between potential false positives and
false negatives.

This commit disjoins a regexp employing these heuristics to the
existing Scheme regexp, so it will still match everything that it did
previously.

Author: slburson

userdiff.c

@@ -249,14 +249,6 @@ PATTERNS("kotlin",
 	 "|[.][0-9][0-9_]*([Ee][-+]?[0-9]+)?[fFlLuU]?"
 	 /* unary and binary operators */
 	 "|[-+*/<>%&^|=!]==?|--|\\+\\+|<<=|>>=|&&|\\|\\||->|\\.\\*|!!|[?:.][.:]"),
-PATTERNS("lisp",
-	 /* Either an unindented left paren, or a slightly indented line
-	  * starting with "(def" */
-	 "^((\\(|:space:{1,2}\\(def).*)$",
-	 /* Common Lisp symbol syntax allows arbitrary strings between vertical bars */
-	 "\\|([^\\\\]|\\\\\\\\|\\\\\\|)*\\|"
-	 /* All other words are delimited by spaces or parentheses/brackets/braces */
-	 "|([^][(){} \t])+"),
 PATTERNS("markdown",
 	 "^ {0,3}#{1,6}[ \t].*",
 	 /* -- */
@@ -352,14 +344,21 @@ PATTERNS("rust",
 	 "|[0-9][0-9_a-fA-Fiosuxz]*(\\.([0-9]*[eE][+-]?)?[0-9_fF]*)?"
 	 "|[-+*\\/<>%&^|=!:]=|<<=?|>>=?|&&|\\|\\||->|=>|\\.{2}=|\\.{3}|::"),
 PATTERNS("scheme",
-	 "^[\t ]*(\\(((define|def(struct|syntax|class|method|rules|record|proto|alias)?)[-*/ \t]|(library|module|struct|class)[*+ \t]).*)$",
+	 /* A possibly indented left paren followed by a Scheme keyword. */
+	 "^[\t ]*(\\(((define|def(struct|syntax|class|method|rules|record|proto|alias)?)[-*/ \t]|(library|module|struct|class)[*+ \t]).*)$\n"
+	 /*
+	  * For other Lisp dialects: either an unindented left paren, or a
+	  * slightly indented line starting with "(def".
+	  */
+	 "^((\\(| {1,2}\\([Dd][Ee][Ff]).*)$",
 	 /*
-	  * R7RS valid identifiers include any sequence enclosed
-	  * within vertical lines having no backslashes
+	  * The union of R7RS and Common Lisp symbol syntax: allows arbitrary
+	  * strings between vertical bars, including escaped backslashes and
+	  * vertical bars.
 	  */
-	 "\\|([^\\\\]*)\\|"
+	 "\\|([^\\\\]|\\\\\\\\|\\\\\\|)*\\|"
 	 /* All other words should be delimited by spaces or parentheses */
-	 "|([^][)(}{[ \t])+"),
+	 "|([^][)(}{ \t])+"),
 PATTERNS("tex", "^(\\\\((sub)*section|chapter|part)\\*{0,1}\\{.*)$",
 	 "\\\\[a-zA-Z@]+|\\\\.|([a-zA-Z0-9]|[^\x01-\x7f])+"),
 { .name = "default", .binary = -1 },