Lua: add a `clone()` method to all AST elements (#5572)

Closes: #5568

5 files changed, 112 insertions, 1 deletions

diff --git a/data/pandoc.lua b/data/pandoc.lua
index 859ecedc4..97e75efca 100644
--- a/data/pandoc.lua
+++ b/data/pandoc.lua
@@ -28,6 +28,7 @@ local M = {}
 M.List = require 'pandoc.List'
 M.mediabag = require 'pandoc.mediabag'
 M.system = require 'pandoc.system'
+M.types = require 'pandoc.types'
 M.utils = require 'pandoc.utils'
 M.text = require 'text'
 
@@ -280,6 +281,7 @@ end
 -- @tparam      {Block,...} blocks      document content
 -- @tparam[opt] Meta        meta        document meta data
 M.Pandoc = AstElement:make_subtype'Pandoc'
+M.Pandoc.behavior.clone = M.types.clone.Pandoc
 function M.Pandoc:new (blocks, meta)
   return {
     blocks = ensureList(blocks),
@@ -299,6 +301,7 @@ M.Doc = M.Pandoc
 -- @function Meta
 -- @tparam meta table table containing document meta information
 M.Meta = AstElement:make_subtype'Meta'
+M.Meta.behavior.clone = M.types.clone.Meta
 function M.Meta:new (meta) return meta end
 
 
@@ -306,6 +309,7 @@ function M.Meta:new (meta) return meta end
 -- MetaValue
 -- @section MetaValue
 M.MetaValue = AstElement:make_subtype('MetaValue')
+M.MetaValue.behavior.clone = M.types.clone.MetaValue
 
 --- Meta blocks
 -- @function MetaBlocks
@@ -369,6 +373,7 @@ end
 
 --- Block elements
 M.Block = AstElement:make_subtype'Block'
+M.Block.behavior.clone = M.types.clone.Block
 
 --- Creates a block quote element
 -- @function BlockQuote
@@ -542,6 +547,7 @@ M.Table = M.Block:create_constructor(
 
 --- Inline element class
 M.Inline = AstElement:make_subtype'Inline'
+M.Inline.behavior.clone = M.types.clone.Inline
 
 --- Creates a Cite inline element
 -- @function Cite
@@ -898,6 +904,7 @@ function M.Attr:new (identifier, classes, attributes)
   attributes = setmetatable(to_alist(attributes or {}), AttributeList)
   return {identifier, classes, attributes}
 end
+M.Attr.behavior.clone = M.types.clone.Attr
 M.Attr.behavior._field_names = {identifier = 1, classes = 2, attributes = 3}
 M.Attr.behavior.__eq = utils.equals
 M.Attr.behavior.__index = function(t, k)
@@ -922,6 +929,7 @@ end
 
 -- Citation
 M.Citation = AstElement:make_subtype'Citation'
+M.Citation.behavior.clone = M.types.clone.Citation
 
 --- Creates a single citation.
 -- @function Citation
@@ -944,6 +952,7 @@ end
 
 -- ListAttributes
 M.ListAttributes = AstElement:make_subtype 'ListAttributes'
+M.ListAttributes.behavior.clone = M.types.clone.ListAttributes
 
 --- Creates a set of list attributes.
 -- @function ListAttributes
diff --git a/doc/lua-filters.md b/doc/lua-filters.md
index 3ac2a62d2..dadc9a2fc 100644
--- a/doc/lua-filters.md
+++ b/doc/lua-filters.md
@@ -644,6 +644,20 @@ This section describes the types of objects available to Lua
 filters. See the [pandoc module](#module-pandoc}) for functions
 to create these objects.
 
+## Shared Properties
+
+### `clone`
+
+`clone ()`
+
+All instances of the types listed here, with the exception of
+read-only objects, can be cloned via the `clone()` method.
+
+Usage:
+
+    local emph = pandoc.Emph {pandoc.Str 'important'}
+    local cloned_emph = emph:clone()  -- note the colon
+
 ## Pandoc {#type-ref-pandoc}
 
 Pandoc document
@@ -1247,6 +1261,7 @@ Object equality is determined via
 :   delimiter of list numbers; one of `DefaultDelim`, `Period`,
     `OneParen`, and `TwoParens` (string)
 
+
 ## Hierarchical Element {#type-ref-Element}
 
 Hierarchical elements can be either *Sec* (sections) or *Blk*
diff --git a/src/Text/Pandoc/Lua/Marshaling/AST.hs b/src/Text/Pandoc/Lua/Marshaling/AST.hs
index f18754ac2..7b428b5f0 100644
--- a/src/Text/Pandoc/Lua/Marshaling/AST.hs
+++ b/src/Text/Pandoc/Lua/Marshaling/AST.hs
@@ -14,7 +14,10 @@
 
 Marshaling/unmarshaling instances for document AST elements.
 -}
-module Text.Pandoc.Lua.Marshaling.AST () where
+module Text.Pandoc.Lua.Marshaling.AST
+  ( LuaAttr (..)
+  , LuaListAttributes (..)
+  ) where
 
 import Prelude
 import Control.Applicative ((<|>))
diff --git a/src/Text/Pandoc/Lua/Module/Types.hs b/src/Text/Pandoc/Lua/Module/Types.hs
index 641bde7d6..fdc63cd99 100644
--- a/src/Text/Pandoc/Lua/Module/Types.hs
+++ b/src/Text/Pandoc/Lua/Module/Types.hs
@@ -15,8 +15,11 @@ module Text.Pandoc.Lua.Module.Types
 import Prelude
 import Data.Version (Version)
 import Foreign.Lua (Lua, NumResults)
+import Text.Pandoc.Definition
+import Text.Pandoc.Lua.Marshaling.AST (LuaAttr, LuaListAttributes)
 import Text.Pandoc.Lua.Marshaling.Version ()
 import Text.Pandoc.Lua.Util (addFunction)
+import Text.Pandoc.Shared (Element (..))
 
 import qualified Foreign.Lua as Lua
 
@@ -25,4 +28,47 @@ pushModule :: Lua NumResults
 pushModule = do
   Lua.newtable
   addFunction "Version" (return :: Version -> Lua Version)
+  pushCloneTable
+  Lua.setfield (Lua.nthFromTop 2) "clone"
   return 1
+
+pushCloneTable :: Lua NumResults
+pushCloneTable = do
+  Lua.newtable
+  addFunction "Attr" cloneAttr
+  addFunction "Block" cloneBlock
+  addFunction "Citation" cloneCitation
+  addFunction "Element" cloneElement
+  addFunction "Inline" cloneInline
+  addFunction "Meta" cloneMeta
+  addFunction "MetaValue" cloneMetaValue
+  addFunction "ListAttributes" cloneListAttributes
+  addFunction "Pandoc" clonePandoc
+  return 1
+
+cloneAttr :: LuaAttr -> Lua LuaAttr
+cloneAttr = return
+
+cloneBlock :: Block -> Lua Block
+cloneBlock = return
+
+cloneCitation :: Citation -> Lua Citation
+cloneCitation = return
+
+cloneElement :: Element -> Lua Element
+cloneElement = return
+
+cloneInline :: Inline -> Lua Inline
+cloneInline = return
+
+cloneListAttributes :: LuaListAttributes -> Lua LuaListAttributes
+cloneListAttributes = return
+
+cloneMeta :: Meta -> Lua Meta
+cloneMeta = return
+
+cloneMetaValue :: MetaValue -> Lua MetaValue
+cloneMetaValue = return
+
+clonePandoc :: Pandoc -> Lua Pandoc
+clonePandoc = return
diff --git a/test/lua/module/pandoc.lua b/test/lua/module/pandoc.lua
index 1c02c8720..ca2168805 100644
--- a/test/lua/module/pandoc.lua
+++ b/test/lua/module/pandoc.lua
@@ -87,6 +87,44 @@ return {
       end)
     },
   },
+
+  group 'clone' {
+    test('clones Attr', function ()
+      local attr = pandoc.Attr('test', {'my-class'}, {foo = 'bar'})
+      local cloned = attr:clone()
+      attr.identifier = ''
+      attr.classes = {}
+      attr.attributes = {}
+      assert.are_same(cloned.identifier, 'test')
+      assert.are_same(cloned.classes, {'my-class'})
+      assert.are_same(cloned.attributes.foo, 'bar')
+    end),
+    test('clones ListAttributes', function ()
+      local la = pandoc.ListAttributes(2, pandoc.DefaultStyle, pandoc.Period)
+      local cloned = la:clone()
+      la.start = 9
+      assert.are_same(cloned.start, 2)
+    end),
+    test('clones Para', function ()
+      local para = pandoc.Para {pandoc.Str 'Hello'}
+      local cloned = para:clone()
+      para.content[1].text = 'bye'
+      assert.are_same(cloned, pandoc.Para {pandoc.Str 'Hello'})
+    end),
+    test('clones Str', function ()
+      local str = pandoc.Str 'Hello'
+      local cloned = str:clone()
+      str.text = 'bye'
+      assert.are_same(cloned.text, 'Hello')
+    end),
+    test('clones Citation', function ()
+      local cite = pandoc.Citation('leibniz', pandoc.AuthorInText)
+      local cloned = cite:clone()
+      cite.id = 'newton'
+      assert.are_same(cloned.id, 'leibniz')
+    end),
+  },
+
   group 'pipe' {
     test('external string processing', function ()
       if os_is_windows() then