feat(presets): add error parsers for built-in presets (#9)

Problem: none of the four presets defined an error_parser, so the
diagnostic infrastructure went unused out of the box.

Solution: add parsers for typst (file:line:col short format), latexmk
(pdflatex file-line-error + summary), and pandoc (parse errors, YAML
exceptions, generic errors). Enable machine-parseable output flags in
typst and latex args. Pandoc parser is shared between markdown and
github presets.

lua/preview/presets.lua

@@ -1,15 +1,108 @@
 local M = {}
 
+---@param stderr string
+---@return preview.Diagnostic[]
+local function parse_typst(stderr)
+  local diagnostics = {}
+  for line in stderr:gmatch('[^\r\n]+') do
+    local file, lnum, col, severity, msg = line:match('^(.+):(%d+):(%d+): (%w+): (.+)$')
+    if lnum then
+      local sev = vim.diagnostic.severity.ERROR
+      if severity == 'warning' then
+        sev = vim.diagnostic.severity.WARN
+      end
+      table.insert(diagnostics, {
+        lnum = tonumber(lnum) - 1,
+        col = tonumber(col) - 1,
+        message = msg,
+        severity = sev,
+        source = file,
+      })
+    end
+  end
+  return diagnostics
+end
+
+---@param stderr string
+---@return preview.Diagnostic[]
+local function parse_latexmk(stderr)
+  local diagnostics = {}
+  for line in stderr:gmatch('[^\r\n]+') do
+    local _, lnum, msg = line:match('^%.?/?(.+%.tex):(%d+): (.+)$')
+    if lnum then
+      table.insert(diagnostics, {
+        lnum = tonumber(lnum) - 1,
+        col = 0,
+        message = msg,
+        severity = vim.diagnostic.severity.ERROR,
+      })
+    else
+      local rule_msg = line:match('^%s+(%S.+gave return code %d+)$')
+      if rule_msg then
+        table.insert(diagnostics, {
+          lnum = 0,
+          col = 0,
+          message = rule_msg,
+          severity = vim.diagnostic.severity.ERROR,
+        })
+      end
+    end
+  end
+  return diagnostics
+end
+
+---@param stderr string
+---@return preview.Diagnostic[]
+local function parse_pandoc(stderr)
+  local diagnostics = {}
+  for line in stderr:gmatch('[^\r\n]+') do
+    local lnum, col, msg = line:match('Error at .+ %(line (%d+), column (%d+)%): (.+)$')
+    if lnum then
+      table.insert(diagnostics, {
+        lnum = tonumber(lnum) - 1,
+        col = tonumber(col) - 1,
+        message = msg,
+        severity = vim.diagnostic.severity.ERROR,
+      })
+    else
+      local ylnum, ycol, ymsg =
+        line:match('YAML parse exception at line (%d+), column (%d+)[,:]%s*(.+)$')
+      if ylnum then
+        table.insert(diagnostics, {
+          lnum = tonumber(ylnum) - 1,
+          col = tonumber(ycol) - 1,
+          message = ymsg,
+          severity = vim.diagnostic.severity.ERROR,
+        })
+      else
+        local errmsg = line:match('^pandoc: (.+)$')
+        if errmsg and not errmsg:match('^Error at') then
+          table.insert(diagnostics, {
+            lnum = 0,
+            col = 0,
+            message = errmsg,
+            severity = vim.diagnostic.severity.ERROR,
+          })
+        end
+      end
+    end
+  end
+  return diagnostics
+end
+
 ---@type preview.ProviderConfig
 M.typst = {
   ft = 'typst',
   cmd = { 'typst', 'compile' },
   args = function(ctx)
-    return { ctx.file }
+    return { '--diagnostic-format', 'short', ctx.file }
   end,
   output = function(ctx)
     return (ctx.file:gsub('%.typ$', '.pdf'))
   end,
+  error_parser = function(stderr)
+    return parse_typst(stderr)
+  end,
   open = true,
 }
 
@@ -18,11 +111,19 @@ M.latex = {
   ft = 'tex',
   cmd = { 'latexmk' },
   args = function(ctx)
-    return { '-pdf', '-interaction=nonstopmode', ctx.file }
+    return {
+      '-pdf',
+      '-interaction=nonstopmode',
+      '-pdflatex=pdflatex -file-line-error -interaction=nonstopmode %O %S',
+      ctx.file,
+    }
   end,
   output = function(ctx)
     return (ctx.file:gsub('%.tex$', '.pdf'))
   end,
+  error_parser = function(stderr)
+    return parse_latexmk(stderr)
+  end,
   clean = function(ctx)
     return { 'latexmk', '-c', ctx.file }
   end,
@@ -40,6 +141,9 @@ M.markdown = {
   output = function(ctx)
     return (ctx.file:gsub('%.md$', '.html'))
   end,
+  error_parser = function(stderr)
+    return parse_pandoc(stderr)
+  end,
   clean = function(ctx)
     return { 'rm', '-f', (ctx.file:gsub('%.md$', '.html')) }
   end,
@@ -67,6 +171,9 @@ M.github = {
   output = function(ctx)
     return (ctx.file:gsub('%.md$', '.html'))
   end,
+  error_parser = function(stderr)
+    return parse_pandoc(stderr)
+  end,
   clean = function(ctx)
     return { 'rm', '-f', (ctx.file:gsub('%.md$', '.html')) }
   end,