rst: single backticks now render correctly in both rst2html and github (#17028)

* rst: `` => `
* support default-role in rst2html
* update docstyle regarding single vs double backticks

lib/packages/docutils/rst.nim

@@ -1978,6 +1978,10 @@ proc dirAdmonition(p: var RstParser, d: string): PRstNode =
   result.kind = rnAdmonition
   result.text = d
 
+proc dirDefaultRole(p: var RstParser): PRstNode =
+  result = parseDirective(p, {hasArg}, nil)
+  result.kind = rnDefaultRole
+
 proc dirRawAux(p: var RstParser, result: var PRstNode, kind: RstNodeKind,
                contentParser: SectionParser) =
   var filename = getFieldValue(result, "file")
@@ -2037,6 +2041,7 @@ proc selectDir(p: var RstParser, d: string): PRstNode =
   of "tip": result = dirAdmonition(p, d)
   of "title": result = dirTitle(p)
   of "warning": result = dirAdmonition(p, d)
+  of "default-role": result = dirDefaultRole(p)
   else:
     rstMessage(p, meInvalidDirective, d)
 

lib/packages/docutils/rstast.nim

@@ -65,6 +65,7 @@ type
     rnInlineTarget,           # "_`target`"
     rnSubstitutionReferences, # "|"
     rnSmiley,                 # some smiley
+    rnDefaultRole,            # .. default-role:: code
     rnLeaf                    # a leaf; the node's text field contains the
                               # leaf val
 

lib/packages/docutils/rstgen.nim

@@ -1293,6 +1293,7 @@ proc renderRstToOut(d: PDoc, n: PRstNode, result: var string) =
   of rnSmiley: renderSmiley(d, n, result)
   of rnLeaf: result.add(esc(d.target, n.text))
   of rnContents: d.hasToc = true
+  of rnDefaultRole: discard
   of rnTitle:
     d.meta[metaTitle] = ""
     renderRstToOut(d, n.sons[0], d.meta[metaTitle])