Configuration option to enable/disable highlighting of discard macro

Disabled by default because we are currently unable to correctly
highlight stacked discard reader macros.

Related: #17

README.md

@@ -36,6 +36,8 @@ regions, such as rainbow parenphesis plugins.)
 
 ### Syntax options
 
+#### `g:clojure_syntax_keywords`
+
 Syntax highlighting of public vars in `clojure.core` is provided by default,
 but additional symbols can be highlighted by adding them to the
 `g:clojure_syntax_keywords` variable.
@@ -58,6 +60,14 @@ will not be highlighted by default.  This is useful for namespaces that have
 set `(:refer-clojure :only [])`.
 
 
+#### `g:clojure_discard_macro`
+
+Set this variable to `1` to enable highlighting of the
+"[discard reader macro](https://clojure.org/guides/weird_characters#_discard)".
+Due to limitations in Vim's syntax rules we cannot correctly highlight stacked
+discard macros (e.g. `#_#_`).
+
+
 ### Indent options
 
 Clojure indentation differs somewhat from traditional Lisps, due in part to

doc/clojure.txt

@@ -115,9 +115,11 @@ clojure-mode.el:
 
 CLOJURE							*ft-clojure-syntax*
 
+						*g:clojure_syntax_keywords*
+
 Syntax highlighting of public vars in "clojure.core" is provided by default,
 but additional symbols can be highlighted by adding them to the
-*g:clojure_syntax_keywords* variable.  The value should be a |Dictionary| of
+|g:clojure_syntax_keywords| variable.  The value should be a |Dictionary| of
 syntax group names, each containing a |List| of identifiers.
 >
 	let g:clojure_syntax_keywords = {
@@ -135,11 +137,26 @@ By setting the *b:clojure_syntax_without_core_keywords* variable, vars from
 "clojure.core" will not be highlighted by default.  This is useful for
 namespaces that have set `(:refer-clojure :only [])`
 
-Setting *g:clojure_fold* to `1` will enable the folding of Clojure code.  Any
+
+							*g:clojure_fold*
+
+Setting |g:clojure_fold| to `1` will enable the folding of Clojure code.  Any
 list, vector or map that extends over more than one line can be folded using
 the standard Vim |fold-commands|.
 
 
+							*g:clojure_discard*
+
+Set this variable to `1` to enable basic highlighting of Clojure's "discard
+reader macro".
+>
+	#_(defn foo [x]
+	    (println x))
+<
+Note that this option will not correctly highlight stacked discard macros
+(e.g. `#_#_`).
+
+
 ABOUT							*clojure-about*
 
 This document and associated runtime files are maintained at:

syntax/clojure.vim

@@ -136,16 +136,17 @@ syntax match clojureComment "#!.*$"
 syntax match clojureComment ","
 
 " Comment out discarded forms.  <https://clojure.org/guides/weird_characters#_discard>
-" TODO: stacking support and/or option to enable/disable this.
-syntax region clojureDiscard matchgroup=clojureDiscard start=/#_[ ,\t\n`'~]*/   end=/[, \t\n()\[\]{}";]/me=e-1
-syntax region clojureDiscard matchgroup=clojureDiscard start=/#_[ ,\t\n`'~]*"/  skip=/\\[\\"]/ end=/"/
-syntax region clojureDiscard matchgroup=clojureDiscard start=/#_[ ,\t\n`'~]*(/  end=/)/  contains=clojureDiscardForm
-syntax region clojureDiscard matchgroup=clojureDiscard start=/#_[ ,\t\n`'~]*\[/ end=/\]/ contains=clojureDiscardForm
-syntax region clojureDiscard matchgroup=clojureDiscard start=/#_[ ,\t\n`'~]*{/  end=/}/  contains=clojureDiscardForm
-
-syntax region clojureDiscardForm start="("  end=")"  contained contains=clojureDiscardForm
-syntax region clojureDiscardForm start="{"  end="}"  contained contains=clojureDiscardForm
-syntax region clojureDiscardForm start="\[" end="\]" contained contains=clojureDiscardForm
+if exists('g:clojure_discard_macro') && g:clojure_discard_macro
+	syntax region clojureDiscard matchgroup=clojureDiscard start=/#_[ ,\t\n`'~]*/   end=/[, \t\n()\[\]{}";]/me=e-1
+	syntax region clojureDiscard matchgroup=clojureDiscard start=/#_[ ,\t\n`'~]*"/  skip=/\\[\\"]/ end=/"/
+	syntax region clojureDiscard matchgroup=clojureDiscard start=/#_[ ,\t\n`'~]*(/  end=/)/  contains=clojureDiscardForm
+	syntax region clojureDiscard matchgroup=clojureDiscard start=/#_[ ,\t\n`'~]*\[/ end=/\]/ contains=clojureDiscardForm
+	syntax region clojureDiscard matchgroup=clojureDiscard start=/#_[ ,\t\n`'~]*{/  end=/}/  contains=clojureDiscardForm
+
+	syntax region clojureDiscardForm start="("  end=")"  contained contains=clojureDiscardForm
+	syntax region clojureDiscardForm start="{"  end="}"  contained contains=clojureDiscardForm
+	syntax region clojureDiscardForm start="\[" end="\]" contained contains=clojureDiscardForm
+endif
 
 " -*- TOP CLUSTER -*-
 " Generated from https://github.com/clojure-vim/clojure.vim/blob/%%RELEASE_TAG%%/clj/src/vim_clojure_static/generate.clj