new feature: comment/uncomment current line or selected lines

This allows for commenting or uncommenting a line or a bunch of lines
with a single keystroke (default binding: M-3).  The characters used
for commenting/uncommenting are specified by the active syntax file.
Reviewed-by: Benno Schulenberg <bensberg@justemail.net>
Signed-off-by: Mike Scalora <mike@scalora.org>

configure.ac

@@ -84,6 +84,22 @@ else
     fi
 fi
 
+AC_ARG_ENABLE(comment,
+AS_HELP_STRING([--disable-comment], [Disable comment/uncomment functions]))
+if test "x$enable_tiny" = xyes; then
+    if test "x$enable_comment" = xyes; then
+	AC_MSG_ERROR([--enable-comment cannot work with --enable-tiny])
+    else
+	# Disabling nanorc silently disables comment support.
+	enable_comment=no
+    fi
+fi
+if test "x$disable_comment" != xyes; then
+    if test "x$enable_comment" != xno; then
+	AC_DEFINE(ENABLE_COMMENT, 1, [Define this to disable the comment/uncomment functionality.])
+    fi
+fi
+
 AC_ARG_ENABLE(extra,
 AS_HELP_STRING([--disable-extra], [Disable extra features, currently only easter eggs]))
 if test "x$enable_extra" = xno; then

doc/man/nanorc.5

@@ -302,6 +302,16 @@ syntax should be used for that file.  This
 functionality only works when \fBlibmagic\fP is installed on the
 system and will be silently ignored otherwise.
 .TP
+.BI comment " string"
+Use the given string for commenting and uncommenting lines.  A vertical bar or
+pipe character (|) designates bracket-style comments; for example, "/*|*/" for
+CSS files.  The characters before the pipe are prepended to the line and the
+characters after the pipe are appended at the end of the line.  If no pipe
+character is present, the entire string is prepended; for example, "#" for
+Python files.  If empty double quotes are specified, the comment/uncomment
+function is disabled; for example, "" for JSON.  Double quotes or backslashes
+may be escaped with a backslash; for example, ".\\"" for man page source.
+.TP
 .B color \fIfgcolor\fR,\fIbgcolor\fR """\fIregex\fR""" ...
 Display all pieces of text that match
 the extended regular expression \fIregex\fP with foreground color
@@ -336,7 +346,7 @@ to \fBicolor\fP.
 .BI extendsyntax " str directive " \fR[ "arg " \fR...]
 Extend the syntax previously defined as \fIstr\fP to include
 new information.  This allows you to add a new \fBcolor\fP, \fBicolor\fP,
-\fBheader\fP, \fBmagic\fP, \fBlinter\fP, or \fBformatter\fP directive
+\fBheader\fP, \fBmagic\fP, \fBcomment\fP, \fBlinter\fP, or \fBformatter\fP directive
 to an already defined syntax -- useful when you want to
 slightly improve a syntax defined in one of the system-installed
 files (which are normally not writable)
@@ -455,6 +465,10 @@ Indents (shifts to the right) the currently marked text.
 .B unindent
 Unindents (shifts to the left) the currently marked text.
 .TP
+.B comment
+Comments or uncomments the current line or marked lines, using the comment
+style specified in the active syntax.
+.TP
 .B left
 Goes left one position (in the editor or browser).
 .TP

doc/syntax/asm.nanorc

@@ -2,6 +2,7 @@
 
 syntax "asm" "\.(S|s|asm)$"
 magic "[Aa]ssembl(y|er)"
+comment "//"
 
 color red "\<[A-Z_]{2,}\>"
 color brightgreen "\.(data|subsection|text)"

doc/syntax/autoconf.nanorc

 ## Here is an example for Autoconf.
 
 syntax "autoconf" "\.(ac|m4)$"
+comment "#"
 
 # Keywords:
 color yellow "\<(if|test|then|elif|else|fi|for|in|do|done)\>"

doc/syntax/awk.nanorc

@@ -2,6 +2,7 @@
 
 syntax "awk" "\.awk$"
 magic "awk.*script text"
+comment "#"
 
 # Records.
 icolor brightred "\$[0-9A-Z_!@#$*?-]+"

doc/syntax/c.nanorc

@@ -2,6 +2,7 @@
 
 syntax "c" "\.(c(c|pp|xx|\+\+)?|C)$" "\.(h(h|pp|xx)?|H)$" "\.ii?$"
 magic "(ASCII|UTF-8 Unicode) C(\+\+)? program text"
+comment "//"
 
 color brightred "\<[A-Z_][0-9A-Z_]+\>"
 color green "\<(float|double|bool|char|int|short|long|sizeof|enum|void|auto|static|const|struct|union|typedef|extern|(un)?signed|inline)\>"

doc/syntax/cmake.nanorc

 ## Syntax highlighting for CMake files.
 
 syntax "cmake" "(CMakeLists\.txt|\.cmake)$"
+comment "#"
 
 icolor green "^[[:space:]]*[A-Z0-9_]+"
 icolor brightyellow "^[[:space:]]*(include|include_directories|include_external_msproject)\>"

doc/syntax/css.nanorc

 ## Here is an example for CSS files.
 
 syntax "css" "\.css$"
+comment "/*|*/"
 
 color brightred     "."
 color brightyellow  start="\{" end="\}"

doc/syntax/debian.nanorc

 ## Here is an example for apt's sources.list.
 
 syntax "sources.list" "sources\.list(~|\.old|\.save)?$" "sources\.list\.d/.*\.list(~|\.old|\.save)?$"
+comment "#"
 
 # Coloring the deb lines, working from tail to head.  First the
 # components -- well, everything, and thus also the components.

doc/syntax/default.nanorc

@@ -2,6 +2,7 @@
 ## for files that do not match any other syntax.
 
 syntax "default"
+comment "#"
 
 # Spaces in front of tabs.
 color ,red " +	+"

doc/syntax/elisp.nanorc

 ## Here is an example for Emacs Lisp.
 
 syntax "elisp" "\.el$"
+comment ";"
 
 # Basic functions/macros
 color brightcyan "\<(if|when|unless|cond|and|or|lambda|let|progn|while|dolist|dotimes)\>"

doc/syntax/fortran.nanorc

 ## Here is an example for Fortran 90/95.
 
 syntax "fortran" "\.(f|f90|f95)$"
+comment "!"
 
 color red "\<[0-9]+\>"
 

doc/syntax/gentoo.nanorc

 ## Here is an example for Gentoo ebuilds/eclasses.
 
 syntax "ebuild" "\.e(build|class)$"
+comment "#"
 
 ## All the standard portage functions
 color brightgreen "(^|\<default_)src_(unpack|prepare|configure|compile|install|test)\>"

doc/syntax/go.nanorc

 ## Here is an example for Go.
 
 syntax "go" "\.go$"
+comment "//"
 
 # Set up a formatter since spelling is probably useless...
 formatter gofmt -w

doc/syntax/groff.nanorc

 ## Here is an example for groff.
 
 syntax "groff" "\.m[ems]$" "\.rof" "\.tmac$" "^tmac."
+comment ".\""
 
 # The argument of .ds or .nr
 color cyan "^\.(ds|nr) [^[:space:]]*"

doc/syntax/guile.nanorc

@@ -3,6 +3,7 @@
 syntax "guile" "\.scm$"
 header "^#!.*guile"
 magic "guile"
+comment ";"
 
 # Basic scheme functions
 color green "\<(do|if|lambda|let(rec)?|map|unless|when)\>"

doc/syntax/html.nanorc

@@ -2,7 +2,10 @@
 
 syntax "html" "\.html?$"
 magic "HTML document text"
+comment "<!--|-->"
 
 color cyan start="<" end=">"
 color red "&[^;[:space:]]*;"
 color green ""(\\.|[^"])*""
+
+color yellow start="<!--" end="-->"

doc/syntax/java.nanorc

@@ -2,6 +2,7 @@
 
 syntax "java" "\.java$"
 magic "Java "
+comment "//"
 
 color green "\<(boolean|byte|char|double|float|int|long|new|short|this|transient|void)\>"
 color red "\<(break|case|catch|continue|default|do|else|finally|for|if|return|switch|throw|try|while)\>"

doc/syntax/javascript.nanorc

 ## Here is an example for Javascript.
 
 syntax "javascript" "\.js$"
+comment "//"
 
 color brightred "\<[A-Z_][0-9A-Z_]+\>"
 color green "\<(const|function|let|this|typeof|var|void)\>"

doc/syntax/json.nanorc

@@ -5,6 +5,8 @@
 # License:  GPLv3 or newer
 
 syntax "json" "\.json$"
+# No comments are permitted in JSON.
+comment ""
 
 # Numbers (used as value).
 color green ":[[:space:]]*\-?(0|[1-9][0-9]*)(\.[0-9]+)?([Ee]?[-+]?[0-9]+)?"