Optimise string building with iodata (#478)

lib/livebook/intellisense.ex

@@ -428,8 +428,7 @@ defmodule Livebook.Intellisense do
 
     inner
     |> String.split("\n")
-    |> Enum.map(&("> " <> &1))
-    |> Enum.join("\n")
+    |> Enum.map_intersperse("\n", &["> ", &1])
   end
 
   defp render_unordered_list(content) do

lib/livebook/live_markdown/export.ex

@@ -14,7 +14,7 @@ defmodule Livebook.LiveMarkdown.Export do
   end
 
   defp render_notebook(notebook) do
-    name = "# #{notebook.name}"
+    name = ["# ", notebook.name]
     sections = Enum.map(notebook.sections, &render_section(&1, notebook))
 
     [name | sections]
@@ -23,7 +23,7 @@ defmodule Livebook.LiveMarkdown.Export do
   end
 
   defp render_section(section, notebook) do
-    name = "## #{section.name}"
+    name = ["## ", section.name]
 
     {cells, _} =
       Enum.map_reduce(section.cells, nil, fn cell, prev_cell ->
@@ -61,14 +61,10 @@ defmodule Livebook.LiveMarkdown.Export do
   end
 
   defp render_cell(%Cell.Elixir{} = cell) do
+    delimiter = code_block_delimiter(cell.source)
     code = get_elixir_cell_code(cell)
-    delimiter = code_block_delimiter(code)
 
-    """
-    #{delimiter}elixir
-    #{code}
-    #{delimiter}\
-    """
+    [delimiter, "elixir\n", code, "\n", delimiter]
     |> prepend_metadata(cell.metadata)
   end
 
@@ -141,9 +137,7 @@ defmodule Livebook.LiveMarkdown.Export do
 
   defp format_code(code) do
     try do
-      code
-      |> Code.format_string!()
-      |> IO.iodata_to_binary()
+      Code.format_string!(code)
     rescue
       _ -> code
     end

lib/livebook/live_markdown/markdown_helpers.ex

@@ -161,38 +161,38 @@ defmodule Livebook.LiveMarkdown.MarkdownHelpers do
   @void_elements ~W(area base br col command embed hr img input keygen link meta param source track wbr)
 
   defp render_html(tag, attrs, []) when tag in @void_elements do
-    "<#{tag} #{attrs_to_string(attrs)} />"
+    ["<", tag, " ", attrs_to_string(attrs), " />"]
   end
 
   defp render_html(tag, attrs, lines) do
-    inner = Enum.join(lines, "\n")
-    "<#{tag} #{attrs_to_string(attrs)}>\n#{inner}\n</#{tag}>"
+    inner = Enum.intersperse(lines, "\n")
+    ["<", tag, " ", attrs_to_string(attrs), ">\n", inner, "\n</", tag, ">"]
   end
 
   defp render_emphasis(content) do
     inner = markdown_from_ast(content)
-    "*#{inner}*"
+    ["*", inner, "*"]
   end
 
   defp render_strong(content) do
     inner = markdown_from_ast(content)
-    "**#{inner}**"
+    ["**", inner, "**"]
   end
 
   defp render_strikethrough(content) do
     inner = markdown_from_ast(content)
-    "~~#{inner}~~"
+    ["~~", inner, "~~"]
   end
 
   defp render_code_inline(content) do
     inner = markdown_from_ast(content)
-    "`#{inner}`"
+    ["`", inner, "`"]
   end
 
   defp render_link(content, attrs) do
-    caption = markdown_from_ast(content)
+    caption = build_md([], content)
     href = get_attr(attrs, "href", "")
-    "[#{caption}](#{href})"
+    ["[", caption, "](", href, ")"]
   end
 
   defp render_image(attrs) do
@@ -201,15 +201,15 @@ defmodule Livebook.LiveMarkdown.MarkdownHelpers do
     title = get_attr(attrs, "title", "")
 
     if title == "" do
-      "![#{alt}](#{src})"
+      ["![", alt, "](", src, ")"]
     else
-      ~s/![#{alt}](#{src} "#{title}")/
+      ["![", alt, "](", src, ~s/ "/, title, ~s/")/]
     end
   end
 
   defp render_comment([line]) do
     line = String.trim(line)
-    "<!-- #{line} -->"
+    ["<!-- ", line, " -->"]
   end
 
   defp render_comment(lines) do
@@ -220,7 +220,7 @@ defmodule Livebook.LiveMarkdown.MarkdownHelpers do
       |> Enum.drop_while(&blank?/1)
       |> Enum.reverse()
 
-    Enum.join(["<!--" | lines] ++ ["-->"], "\n")
+    ["<!--\n", Enum.intersperse(lines, "\n"), "\n-->"]
   end
 
   defp render_ruler(attrs) do
@@ -238,13 +238,13 @@ defmodule Livebook.LiveMarkdown.MarkdownHelpers do
   defp render_paragraph(content), do: markdown_from_ast(content)
 
   defp render_heading(n, content) do
-    title = markdown_from_ast(content)
-    String.duplicate("#", n) <> " " <> title
+    title = build_md([], content)
+    [String.duplicate("#", n), " ", title]
   end
 
   defp render_code_block(content, attrs) do
     language = get_attr(attrs, "class", "")
-    "```#{language}\n#{content}\n```"
+    ["```", language, "\n", content, "\n```"]
   end
 
   defp render_blockquote(content) do
@@ -252,8 +252,7 @@ defmodule Livebook.LiveMarkdown.MarkdownHelpers do
 
     inner
     |> String.split("\n")
-    |> Enum.map(&("> " <> &1))
-    |> Enum.join("\n")
+    |> Enum.map_intersperse("\n", &["> ", &1])
   end
 
   defp render_table([{"thead", _, [head_row], %{}}, {"tbody", _, body_rows, %{}}]) do
@@ -275,7 +274,7 @@ defmodule Livebook.LiveMarkdown.MarkdownHelpers do
   defp cell_grid_from_rows(rows) do
     Enum.map(rows, fn {"tr", _, columns, %{}} ->
       Enum.map(columns, fn {tag, _, content, %{}} when tag in ["th", "td"] ->
-        markdown_from_ast(content)
+        build_md([], content)
       end)
     end)
   end
@@ -308,7 +307,7 @@ defmodule Livebook.LiveMarkdown.MarkdownHelpers do
     |> Enum.map(&Tuple.to_list/1)
     |> Enum.map(fn cells ->
       cells
-      |> Enum.map(&String.length/1)
+      |> Enum.map(&IO.iodata_length/1)
       |> Enum.max()
     end)
   end
@@ -317,16 +316,18 @@ defmodule Livebook.LiveMarkdown.MarkdownHelpers do
     cells
     |> Enum.zip(widths)
     |> Enum.map(fn {cell, width} ->
-      String.pad_trailing(cell, width, " ")
+      length = IO.iodata_length(cell)
+      missing = max(width - length, 0)
+      [cell, String.duplicate(" ", missing)]
     end)
   end
 
   defp cell_grid_to_md_table(cell_grid) do
     cell_grid
     |> Enum.map(fn cells ->
-      "| " <> Enum.join(cells, " | ") <> " |"
+      ["| ", Enum.intersperse(cells, " | "), " |"]
     end)
-    |> Enum.join("\n")
+    |> Enum.intersperse("\n")
   end
 
   defp render_unordered_list(content) do
@@ -349,17 +350,17 @@ defmodule Livebook.LiveMarkdown.MarkdownHelpers do
     |> Enum.map(fn {inner, index} ->
       [first_line | lines] = String.split(inner, "\n")
 
-      first_line = marker_fun.(index) <> first_line
+      first_line = [marker_fun.(index), first_line]
 
       lines =
         Enum.map(lines, fn
           "" -> ""
-          line -> indent <> line
+          line -> [indent, line]
         end)
 
-      Enum.join([first_line | lines], "\n")
+      Enum.intersperse([first_line | lines], "\n")
     end)
-    |> Enum.join(item_separator)
+    |> Enum.intersperse(item_separator)
   end
 
   defp spaced_list_items?([{"li", _, [{"p", _, _content, %{}} | _], %{}} | _items]), do: true