[Pandoc Writer] Misc. Improvements

* New `html_attributes()` func. to convert pandoc
  attributes to PML HTML Attributes by prefixing
  `html_` to their key. Unfortunately can't be used
  due PMLC 3.1.0 bug (see: pml-lang/pml-companion#91)
* Adapt `Span()` element, but temporarily ignore any
  HTML attributes due to current PMLC bug.
* Implement `SingleQuoted()` and `DoubleQuoted()` by
  emitting literal curly quotes characters.
* Tweak `Link()` and stop escaping the value of `text`
  attribute, since it would vanquish any inline styles
  (although it seems that no styles are supported).

pandoc/filters-lua/pml-writer/pml-writer.lua

@@ -1,4 +1,4 @@
--- "pml-writer.lua" v0.0.11 | 2022/11/03             | PML 3.1.0 | pandoc 2.19.2
+-- "pml-writer.lua" v0.0.12 | 2022/11/03             | PML 3.1.0 | pandoc 2.19.2
 -- =============================================================================
 -- ** WARNING ** This PML writer is being built on top of the sample writer that
 --               ships with pandoc; generated via:
@@ -154,6 +154,23 @@ local function pml_node_verbatim(s)
   return '[verbatim ' .. s .. ']'
 end
 
+-- Helper function to convert an attributes table into
+-- an HTML attribute string that can be injected into PML nodes.
+-- @WIP: html_attributes()
+local function html_attributes(attr)
+  -- @NOTE: A bug in PML 3.1.0 causes multiple 'html_*' attributes to crash,
+  --        so this function can't be used safely until next PMLC release.
+  --        See: pml-lang/pml-companion#91
+  local attr_table = {}
+  for x,y in pairs(attr) do
+    if y and y ~= '' then
+      -- @TODO: Use dedicated quoted attributes escaping function
+      table.insert(attr_table, ' html_' .. x .. '="' .. escape(y,true) .. '"')
+    end
+  end
+  return table.concat(attr_table)
+end
+
 
 -- *****************************************************************************
 --
@@ -219,7 +236,10 @@ function Link(s, tgt, tit, attr)
     return escape(s)
   end
   -- @TODO: Add a dedicated URL escape function:
-  return '[link url=' .. tgt .. ' text="' .. escape(s) .. '"]'
+  -- @NOTE: Removed escaping of 'text' value since it might contain
+  --        styled contents, although these don't seem to work in PML:
+  return '[link url=' .. tgt .. ' text="' .. s .. '"]'
+--return '[link url=' .. tgt .. ' text="' .. escape(s) .. '"]'
 --[[
   return '<a href="' .. escape(tgt,true) .. '" title="' ..
          escape(tit,true) .. '"' .. attributes(attr) .. '>' .. s .. '</a>'
@@ -254,14 +274,12 @@ function DisplayMath(s)
   return '\\[' .. escape(s) .. '\\]'
 end
 
--- @TBD: SingleQuoted()
 function SingleQuoted(s)
-  return '&lsquo;' .. s .. '&rsquo;'
+  return '‘' .. s .. '’'
 end
 
--- @TBD: DoubleQuoted()
 function DoubleQuoted(s)
-  return '&ldquo;' .. s .. '&rdquo;'
+  return '“' .. s .. '”'
 end
 
 -- @TBD: Note()
@@ -277,9 +295,13 @@ function Note(s)
             '"><sup>' .. num .. '</sup></a>'
 end
 
--- @TBD: Span()
+-- @WIP: Span()
 function Span(s, attr)
-  return '<span' .. attributes(attr) .. '>' .. s .. '</span>'
+  -- @TODO: A bug in PML 3.1.0 causes multiple 'html_*' attributes to crash,
+  --        so we temporarily need to suppress html attributes until fixed.
+  --        See: pml-lang/pml-companion#91
+  return '[span ' .. s .. ']'
+  -- return '[span (' .. html_attributes(attr) .. ' ) ' .. s .. ']'
 end
 
 -- @WIP: RawInline()

pandoc/filters-lua/pml-writer/tests/STATUS.md

@@ -20,8 +20,10 @@ Overall progress of the pandoc filter, pending tasks and known issues.
     - [Metadata](#metadata)
     - [TOC Settings](#toc-settings)
 - [Known Issues](#known-issues)
+    - [Links Text](#links-text)
     - [Headings Conversion](#headings-conversion)
     - [List Start Number](#list-start-number)
+    - [HTML Attributes](#html-attributes)
 - [Code Improvements and Sanitation](#code-improvements-and-sanitation)
 
 <!-- /MarkdownTOC -->
@@ -41,7 +43,7 @@ Status of pandoc AST nodes conversion functions, by function names to ease sourc
 - [ ] `DefinitionList()` &rarr; no PML equivalent!
 - [ ] `DisplayMath()`
 - [ ] `Div()`
-- [ ] `DoubleQuoted()`
+- [x] `DoubleQuoted()` &rarr; via literal `“` and `”` curly quote characters.
 - [x] `Emph()`
 - [x] `Header()` — works, but only if doc has Level 1 internal headings.
 - [x] `HorizontalRule()` &rarr; `[html` + `<hr/>`
@@ -56,11 +58,11 @@ Status of pandoc AST nodes conversion functions, by function names to ease sourc
 - [ ] `Plain()`
 - [x] `RawBlock()` — only HTML contents are preserved.
 - [x] `RawInline()` &rarr; `[verbatim` — only HTML contents are preserved.
-- [ ] `SingleQuoted()`
+- [x] `SingleQuoted()` &rarr; via literal `‘` and `’` curly quote characters.
 - [x] `SmallCaps()` &rarr; `[span (html_style=`
 - [x] `SoftBreak()` &rarr; `\n`
 - [x] `Space()`
-- [ ] `Span()`
+- [ ] `Span()` &rarr; `[span` — WIP, but HTML Attributes are suppressed to due PMLC bug (See: [Issue #91]).
 - [x] `Str()`
 - [x] `Strikeout()`
 - [x] `Strong()`
@@ -109,6 +111,16 @@ Some of pandoc TOC settings should be portable to PML via `[doc [options` sub-no
 
 Problems that need addressing and which we are already aware of.
 
+## Links Text
+
+When rendering links as `[link` nodes, if we escape the contents of the `text` attributes it will also escape any formatting nodes therein, so I temporarily skipped escaping altogether, in order to preserve the tags.
+
+But I noticed that the resulting PML code is not being styled, and I'm not sure if it's because the `[link` node doesn't support further styling. In any case, since pandoc supports styles in links text, I'll have to address the problem, by either:
+
+- correctly styling link text according to PML rules,
+- stripping away the styles, or
+- rendering the links as raw HTML (when styled only?)
+
 ## Headings Conversion
 
 When converting from pandoc markdown, the filter expects all in-document headings to be Level 1. If the author considers the document `title` (metadata) as the Level-1 entry, and uses Level 2 headings only withing the document (i.e. `##`) then the filter will produce an extra closing bracket at the document end, resulting in an error.
@@ -117,8 +129,13 @@ I need to find a way to track when there's a discrepancy between expected and ac
 
 ## List Start Number
 
-The code that handles the list `start` attribute has been implemented in the filter, but it had to be circumvented because `html_start` crashes PMLC 3.1.0 due to a bug. (See: [Issue #91](https://github.com/pml-lang/pml-companion/issues/91))
+The code that handles the list `start` attribute has been implemented in the filter, but it had to be circumvented because `html_start` crashes PMLC 3.1.0 due to a bug. (See: [Issue #91])
 
+## HTML Attributes
+
+Currently, due to the PMLC 3.1.0 bug mentioned in [Issue #91], which crashes PMLC when a node has multiple HTML attributes, we had to temporary suppress emitting HTML attributes in the output. This is affecting:
+
+- `Span()` and [text highlighting via `.mark`](https://pandoc.org/MANUAL.html#highlighting)
 
 # Code Improvements and Sanitation
 
@@ -149,4 +166,8 @@ The Lua writer code could still be optimized, and there are aspects of the conve
 
 [node escaping rules]: https://www.pml-lang.dev/docs/user_manual/index.html#node_escape_characters "PML User Manual » Escape Characters » Nodes"
 
+<!-- Issues & Discussions -->
+
+[Issue #91]: https://github.com/pml-lang/pml-companion/issues/91 "Issue #91 — Bug in PMLC 3.1.0 causes crash with multiple HTML attributes"
+
 <!-- EOF -->

pandoc/filters-lua/pml-writer/tests/elements/mark.markdown

@@ -0,0 +1,21 @@
+---
+title: 'Span Test'
+subtitle: "Rendering span nodes"
+author: Tristano Ajmone
+date: 2022-11-03
+...
+
+
+To highlight text, use the `mark` class (via `bracketed_spans` ext.):
+
+> Some [highlighted text]{.mark} example.
+
+Or, via the `native_spans` extension, only for HTML output:
+
+> Some <span class="mark">highlighted text</span> example.
+
+**References:**
+
+- [Pandoc Manual » Highlighting](https://pandoc.org/MANUAL.html#highlighting)
+- [`bracketed_spans`](https://pandoc.org/MANUAL.html#extension-bracketed_spans)
+- [`native_spans`](https://pandoc.org/MANUAL.html#extension-native_spans)

pandoc/filters-lua/pml-writer/tests/elements/mark.pml

@@ -0,0 +1,30 @@
+[doc [title Span Test]
+     [subtitle Rendering span nodes]
+
+Tristano Ajmone |
+2022-11-03
+
+
+To highlight text, use the [c mark] class (via [c bracketed_spans] ext.):
+
+[quote
+Some [span highlighted text] example.
+]
+
+Or, via the [c native_spans] extension, only for HTML output:
+
+[quote
+Some [span highlighted text] example.
+]
+
+[b References:]
+
+[list
+[el [link url=https://pandoc.org/MANUAL.html#highlighting text="Pandoc Manual » Highlighting"]]
+[el [link url=https://pandoc.org/MANUAL.html#extension-bracketed_spans text="[c bracketed_spans]"]]
+[el [link url=https://pandoc.org/MANUAL.html#extension-native_spans text="[c native_spans]"]]
+]
+
+
+
+]

pandoc/filters-lua/pml-writer/tests/elements/quotes.markdown

@@ -0,0 +1,11 @@
+---
+title: 'Curly Quotes Test'
+subtitle: "Rendering typographic single- and double-quotes."
+author: Tristano Ajmone
+date: 2022-11-03
+...
+
+
+'single quoted text'
+
+"double quoted text"

pandoc/filters-lua/pml-writer/tests/elements/quotes.pml

@@ -0,0 +1,14 @@
+[doc [title Curly Quotes Test]
+     [subtitle Rendering typographic single- and double-quotes.]
+
+Tristano Ajmone |
+2022-11-03
+
+
+‘single quoted text’
+
+“double quoted text”
+
+
+
+]

pandoc/filters-lua/pml-writer/tests/elements/span.markdown

@@ -0,0 +1,8 @@
+---
+title: 'Span Test'
+subtitle: "Rendering span nodes"
+author: Tristano Ajmone
+date: 2022-11-03
+...
+
+This is [spanned text]{.my_class} with class `my_class`.

pandoc/filters-lua/pml-writer/tests/elements/span.pml

@@ -0,0 +1,12 @@
+[doc [title Span Test]
+     [subtitle Rendering span nodes]
+
+Tristano Ajmone |
+2022-11-03
+
+
+This is [span spanned text] with class [c my_class].
+
+
+
+]

pandoc/filters-lua/pml-writer/tests/features/writers-lang-and-dir.pml

@@ -12,7 +12,7 @@ div contents</div>
 
 and more text.
 
-Next paragraph with a <span>span</span> and a word-thatincludesa<span>span</span>right?
+Next paragraph with a [span span] and a word-thatincludesa[span span]right?
 
 ][ch [title Directionality]
 
@@ -24,9 +24,9 @@ rtl div contents</div>
 and more text.
 
 <div dir="ltr">
-and a ltr div. with a <span dir="rtl">rtl span</span>.</div>
+and a ltr div. with a [span rtl span].</div>
 
-Next paragraph with a <span dir="rtl">rtl span</span> and a word-that-includesa<span dir="ltr">ltrspan</span>right?
+Next paragraph with a [span rtl span] and a word-that-includesa[span ltrspan]right?
 
 ][ch [title Languages]
 
@@ -37,9 +37,9 @@ German div contents</div>
 
 and more text.
 
-Next paragraph with a <span lang="en-GB">British span</span> and a word-that-includesa<span lang="de-CH">Swiss German span</span>right?
+Next paragraph with a [span British span] and a word-that-includesa[span Swiss German span]right?
 
-Some <span lang="es">Spanish text</span>.
+Some [span Spanish text].
 
 ][ch [title Combined]
 
@@ -50,7 +50,7 @@ French rtl div contents</div>
 
 and more text.
 
-Next paragraph with a <span lang="en-GB" dir="ltr">British ltr span</span> and a word-that-includesa<span lang="de-CH" dir="ltr">Swiss German ltr span</span>right?
+Next paragraph with a [span British ltr span] and a word-that-includesa[span Swiss German ltr span]right?
 
 
 ]