Add table column alignment in IO.ANSI.Docs (#6230)

This commit adds table alignment in markdown which allows the following
for tables:

    right aligned | center aligned | left aligned
    -: | :-: | :-
    a | b | c

This will output a table in the following format:

    right aligned | center aligned  | left aligned
                a |        b        | c

If headings are set, the header line (the line immediately below the
headings is ignored when calculating the max width for the columns.
All lines are trimmed of additional whitespace leading and trailing
whitespace to prevent tables that look like:

    right aligned | center aligned | left aligned
    ------------: | :------------: | :-
         a        |        b       | c

    right aligned | center aligned  | left aligned
         a        |      b          | c

Author: Gazler

lib/elixir/lib/io/ansi/docs.ex

@@ -269,7 +269,11 @@ defmodule IO.ANSI.Docs do
 
     widths =
       for line <- lines do
-        for {_col, length} <- line, do: length
+        if table_header?(line) do
+          for _ <- line, do: 0
+        else
+          for {_col, length} <- line, do: length
+        end
       end
 
     col_widths = Enum.reduce(widths,
@@ -291,6 +295,7 @@ defmodule IO.ANSI.Docs do
     col =
       col
       |> String.replace("\\\|", "|")
+      |> String.trim()
       |> handle_links
       |> handle_inline(options)
     {col, length_without_escape(col, 0)}
@@ -306,6 +311,8 @@ defmodule IO.ANSI.Docs do
   defp render_table([first, second | rest], widths, options) do
     combined = Enum.zip(first, widths)
     if table_header?(second) do
+      alignments = Enum.map(second, &column_alignment/1)
+      options = Keyword.put_new(options, :alignments, alignments)
       draw_table_row(combined, options, :heading)
       render_table(rest, widths, options)
     else
@@ -323,6 +330,14 @@ defmodule IO.ANSI.Docs do
   defp render_table([], _, _),
     do: nil
 
+  defp column_alignment({line, _}) do
+    cond do
+      String.starts_with?(line, ":") and String.ends_with?(line, ":") -> :center
+      String.ends_with?(line, ":") -> :right
+      true -> :left
+    end
+  end
+
   defp table_header?(row) do
     Enum.all?(row, fn {col, _} -> table_header_column?(col) end)
   end
@@ -336,10 +351,13 @@ defmodule IO.ANSI.Docs do
   defp table_header_contents?(_), do: false
 
   defp draw_table_row(cols_and_widths, options, heading \\ false) do
+    default_alignments = List.duplicate(:left, length(cols_and_widths))
+    alignments = Keyword.get(options, :alignments, default_alignments)
+
     columns =
-      Enum.map_join(cols_and_widths, " | ", fn {{col, length}, width} ->
-        col <> String.duplicate(" ", width - length)
-      end)
+      cols_and_widths
+      |> Enum.zip(alignments)
+      |> Enum.map_join(" | ", &generate_table_cell/1)
 
     if heading do
       write(:doc_table_heading, columns, options)
@@ -348,6 +366,20 @@ defmodule IO.ANSI.Docs do
     end
   end
 
+  defp generate_table_cell({{{col, length}, width}, :center}) do
+    pad = if rem(length, 2) == 0, do: 1, else: rem(width, 2)
+    spaces = div(width, 2) - div(length, 2)
+    String.duplicate(" ", spaces) <> col <> String.duplicate(" ", spaces + pad)
+  end
+
+  defp generate_table_cell({{{col, length}, width}, :right}) do
+    String.duplicate(" ", width - length) <> col
+  end
+
+  defp generate_table_cell({{{col, length}, width}, _}) do
+    col <> String.duplicate(" ", width - length)
+  end
+
   defp table_line?(line) do
     line =~ " | "
   end

lib/elixir/test/elixir/io/ansi/docs_test.exs

@@ -303,6 +303,24 @@ defmodule IO.ANSI.DocsTest do
            "\e[7mcolumn 1 | and 2\e[0m\na        | b    \none      | two  \n\e[0m"
   end
 
+  test "table with heading alignment" do
+    table = """
+    column 1 | 2        | and three
+    -------: | :------: | :-----
+        a    |  even    | c\none | odd | three
+    """
+
+    expected = """
+    \e[7m\
+    column 1 |   2   | and three\e[0m
+           a | even  | c        
+         one |  odd  | three    
+    \e[0m
+    """ |> String.trim_trailing
+
+    assert format(table) == expected
+  end
+
   test "table with formatting in cells" do
     assert format("`a` | _b_\nc | d") ==
            "\e[36ma\e[0m | \e[4mb\e[0m\nc | d\n\e[0m"