fix(typst): clean up latent bugs in CSS translator

While writing tests for #14460, found and fixed five latent bugs in
src/resources/filters/modules/typst_css.lua:

- parse_color: brand-color reference path (var(--brand-NAME)) crashed
  when NAME contained digits. The capture class [%a--]* excluded %d, so
  e.g. var(--brand-red-50) failed to match and fell into a broken error
  branch that concatenated an undefined `v` and `return null`. Widened
  the class to [%w-] and fixed the error branch to use the actual color
  string and return nil.

- output_color: implicit global `zero` (missing `local`) leaked from the
  no-color-with-opacity path. Made it local.

- translate_font_weight: passed `null` (an undefined global -> nil) to
  output_warning, silently bypassing any user-supplied warnings
  collector. Changed to forward `warnings`.

- consume_width / consume_style: `fbeg, fend = ...` without `local`
  leaked them as globals on every call. Added `local`.

Each fix is covered by a regression test in tests/unit-lua/typst-css.test.lua.

Author: gordonwoodhull

news/changelog-1.10.md

@@ -16,7 +16,7 @@ All changes included in 1.10:
 ### `typst`
 
 - ([#14261](https://github.com/quarto-dev/quarto-cli/issues/14261)): Fix theorem/example block titles containing inline code producing invalid Typst markup when syntax highlighting is applied.
-- ([#14460](https://github.com/quarto-dev/quarto-cli/issues/14460)): Fix CSS `border` and `border-color` declarations losing tokens that precede an `rgb()`/`rgba()` color (e.g. `border: 0px solid rgb(255, 0, 0)` rendering as a 2.25pt border instead of being suppressed).
+- ([#14460](https://github.com/quarto-dev/quarto-cli/issues/14460)): Fix CSS `border` and `border-color` declarations losing tokens that precede an `rgb()`/`rgba()` color (e.g. `border: 0px solid rgb(255, 0, 0)` rendering as a 2.25pt border instead of being suppressed). Also fixes `var(--brand-NAME)` references crashing the Typst CSS translator when `NAME` contained digits (e.g. `--brand-red-50`).
 
 ### `revealjs`
 

src/resources/filters/modules/typst_css.lua

@@ -305,12 +305,14 @@ local function parse_color(color, warnings)
   elseif color:find '^rgb%(' or color:find '^rgba%(' then
     return parse_rgb(color)
   elseif color:find '^var%(%-%-brand%-' then
-    local colorName = color:match '^var%(%-%-brand%-([%a--]*)%)'
+    -- [%w-] (alphanumerics + hyphen) so names like `red-50` parse. Bare
+    -- [%a--] excluded digits, breaking any brand name with a number.
+    local colorName = color:match '^var%(%-%-brand%-([%w-]*)%)'
     if not colorName then
-      output_warning(warnings, 'invalid brand color reference ' .. v)
-      return null
+      output_warning(warnings, 'invalid brand color reference ' .. color)
+      return nil
     end
-    return colorName and {
+    return {
       type = 'brand',
       value = colorName
     }
@@ -332,7 +334,7 @@ local function output_color(color, opacity, warnings)
   quarto.log.debug('output_color input', color, opacity)
   if opacity then
     if not color then
-      zero = {
+      local zero = {
         unit = 'int',
         value = 0
       }
@@ -627,10 +629,10 @@ local function translate_font_weight(w, warnings)
   if tcontains(same_weights, w) then
     return w
   end
-  if tcontains(dashed_weights, w) then  
+  if tcontains(dashed_weights, w) then
     return w:gsub('-', '')
   else
-    output_warning(null, 'invalid font weight ' .. tostring(w))
+    output_warning(warnings, 'invalid font weight ' .. tostring(w))
     return nil
   end
 end
@@ -716,14 +718,14 @@ local function translate_border(v, warnings)
 end
 
 local function consume_width(s, start, warnings)
-    fbeg, fend = s:find('%S+', start)
-    local term = s:sub(fbeg, fend)
-    local thickness = translate_border_width(term, warnings)
-    return thickness, fend + 1
+  local fbeg, fend = s:find('%S+', start)
+  local term = s:sub(fbeg, fend)
+  local thickness = translate_border_width(term, warnings)
+  return thickness, fend + 1
 end
 
 local function consume_style(s, start, warnings)
-  fbeg, fend = s:find('%S+', start)
+  local fbeg, fend = s:find('%S+', start)
   local term = s:sub(fbeg, fend)
   local dash = translate_border_style(term, warnings)
   return dash, fend + 1

tests/unit-lua/typst-css.test.lua

@@ -150,4 +150,80 @@ function TestTranslateLength:testPassthroughPt()
   lu.assertEquals(typst_css.translate_length('12pt', new_warnings()), '12pt')
 end
 
+-- Bug A: output_color creates `zero` as an implicit global on the no-color
+-- path because the local keyword is missing.
+TestOutputColorGlobalLeak = {}
+
+function TestOutputColorGlobalLeak:setUp()
+  -- Make sure no prior test poisoned this global.
+  rawset(_G, 'zero', nil)
+end
+
+function TestOutputColorGlobalLeak:testNoColorWithOpacityDoesNotLeakGlobal()
+  typst_css.output_color(nil, { unit = 'percent', value = 50 }, new_warnings())
+  lu.assertNil(rawget(_G, 'zero'),
+    'output_color leaked an implicit global "zero"')
+end
+
+-- Bug B+C: parse_color of a brand reference whose name contains digits
+-- (e.g. `--brand-red-50`) currently crashes because:
+--   (B) the [%a--]* class only allows alphas + hyphens, so the capture fails
+--       and the function falls into the error branch
+--   (C) the error branch concatenates a never-defined `v` and returns
+--       `null` (also undefined)
+TestParseColorBrand = {}
+
+function TestParseColorBrand:testBrandNameWithDigitsParses()
+  local c = typst_css.parse_color('var(--brand-red-50)', new_warnings())
+  lu.assertNotIsNil(c)
+  lu.assertEquals(c.type, 'brand')
+  lu.assertEquals(c.value, 'red-50')
+end
+
+function TestParseColorBrand:testMalformedBrandRefReturnsNilNoCrash()
+  -- Anything matching the var(--brand- prefix but failing the name capture
+  -- must not throw a Lua error; it should warn and return nil.
+  local warnings = new_warnings()
+  local ok, c = pcall(typst_css.parse_color, 'var(--brand-!!)', warnings)
+  lu.assertTrue(ok,
+    'parse_color crashed on a malformed brand ref: ' .. tostring(c))
+  lu.assertNil(c)
+end
+
+-- Bug D: translate_font_weight passes `null` (an undefined global -> nil)
+-- to output_warning instead of `warnings`, so the user-supplied warnings
+-- collector is silently bypassed.
+TestTranslateFontWeight = {}
+
+function TestTranslateFontWeight:testInvalidWeightWarnsToCollector()
+  local warnings = new_warnings()
+  local result = typst_css.translate_font_weight('not-a-weight', warnings)
+  lu.assertNil(result)
+  lu.assertEquals(#warnings, 1,
+    'expected the invalid-weight warning to land in the collector, ' ..
+    'but the collector saw ' .. #warnings .. ' warning(s)')
+end
+
+-- Bug E: consume_width and consume_style write `fbeg, fend = ...` without
+-- `local`, leaking them as globals. (consume_color and translate_border
+-- correctly declare them local.)
+TestConsumeNoGlobalLeak = {}
+
+function TestConsumeNoGlobalLeak:setUp()
+  rawset(_G, 'fbeg', nil)
+  rawset(_G, 'fend', nil)
+end
+
+function TestConsumeNoGlobalLeak:testConsumeWidthDoesNotLeak()
+  typst_css.consume_width('2px', 1, new_warnings())
+  lu.assertNil(rawget(_G, 'fbeg'), 'consume_width leaked global "fbeg"')
+  lu.assertNil(rawget(_G, 'fend'), 'consume_width leaked global "fend"')
+end
+
+function TestConsumeNoGlobalLeak:testConsumeStyleDoesNotLeak()
+  typst_css.consume_style('solid', 1, new_warnings())
+  lu.assertNil(rawget(_G, 'fbeg'), 'consume_style leaked global "fbeg"')
+  lu.assertNil(rawget(_G, 'fend'), 'consume_style leaked global "fend"')
+end
+
 os.exit(lu.LuaUnit.run())