feat(core): AST to SIL-like reconstruction helper

core/ast.lua

@@ -0,0 +1,85 @@
+--
+-- SILE AST utilites
+--
+local ast = {}
+
+-- ------------------------------------------------------
+-- AST to SIL: reconstruct a SIL-like output from the AST
+-- ------------------------------------------------------
+
+local function escapeContentString (s)
+  return s:gsub("[%%\\{}]",
+    function(x)
+      return "\\"..x
+    end)
+end
+
+local function escapeParamString (value)
+  local v = tostring(value)
+  return '"' .. v:gsub('"', '\\"') .. '"'
+end
+
+local function optionsToString (options)
+  local out = ""
+  -- options are in an associative table and Lua doesn't guarantee a fixed order.
+  -- To ensure we get a consistent and stable output, rely on alphabetical order.
+  local sortedOpts = {}
+  for k, _ in pairs(options) do table.insert(sortedOpts, k) end
+  table.sort(sortedOpts)
+  if #sortedOpts > 0 then
+    out = out .. "["
+    for iOpt, option in ipairs(sortedOpts) do
+      out = out .. option .. "=" .. escapeParamString(options[option])
+      if iOpt == #sortedOpts then
+        out = out .. "]"
+      else
+        out = out .. ", "
+      end
+    end
+  end
+  return out
+end
+
+-- Environments and commands are the same thing, just a writing convenience.
+local isEnvironment = {
+  document = true,
+}
+
+ast.astToSil = function (content)
+  local out = ""
+  if not content then return out end
+
+  for i = 1, #content do
+    local node = content[i]
+    if type(node) == "string" then
+      out = out .. escapeContentString(node)
+    elseif node.command then
+      if isEnvironment[node.command] then
+        out = out .. "\\begin" .. optionsToString(node.options) .. "{" .. node.command .. "}\n"
+        if (#node >= 1) then
+          out = out .. ast.astToSil(node)
+        end
+        out = out .. "\n\\end{" .. node.command .. "}\n"
+      else
+        out = out .. "\\"  .. node.command .. optionsToString(node.options)
+        if (#node >= 1) then
+          out = out .. "{" .. ast.astToSil(node) .. "}"
+        else
+          out = out .. "{}"
+        end
+      end
+    elseif node.id then
+      -- Due to the way it is implemented, the SILE-inputter may generate such
+      -- nodes in the AST. It's poorly documented, so it's not clear why they
+      -- are even kept there (esp. the id="texlike_stuff" nodes), but anyhow, as
+      -- far concerned for presentation purposes, just recurse into them.
+      out = out .. ast.astToSil(node)
+    else
+      -- Silently recurse into other (nested) tables, i.e. flatten them.
+      out = out .. ast.astToSil(node)
+    end
+  end
+  return out
+end
+
+return ast