Add support for printing tables with borders

Adding borders to tables can improve their legibility.

This would allow replacing the custom table for code statistics in
Rails, with the generic implementation in Thor.

By adding :separators to a table a horizontal separator will be added.
This functionality was inspired by: https://github.com/piotrmurach/tty-table

lib/thor/shell/basic.rb

@@ -175,6 +175,7 @@ def print_in_columns(array)
       # ==== Options
       # indent<Integer>:: Indent the first column by indent value.
       # colwidth<Integer>:: Force the first column to colwidth spaces wide.
+      # borders<Boolean>:: Adds ascii borders.
       #
       def print_table(array, options = {}) # rubocop:disable Metrics/MethodLength
         printer = TablePrinter.new(stdout, options)

lib/thor/shell/table_printer.rb

@@ -4,55 +4,61 @@
 class Thor
   module Shell
     class TablePrinter < ColumnPrinter
+      BORDER_SEPARATOR = :separator
+
       def initialize(stdout, options = {})
         super
         @formats = []
         @maximas = []
         @colwidth = options[:colwidth]
         @truncate = options[:truncate] == true ? Terminal.terminal_width : options[:truncate]
+        @padding = 1
       end
 
       def print(array)
         return if array.empty?
 
         prepare(array)
 
+        print_border_separator if options[:borders]
+
         array.each do |row|
+          if options[:borders] && row == BORDER_SEPARATOR
+            print_border_separator
+            next
+          end
+
           sentence = "".dup
 
           row.each_with_index do |column, index|
-            maxima = @maximas[index]
-
-            f = if column.is_a?(Numeric)
-              if index == row.size - 1
-                # Don't output 2 trailing spaces when printing the last column
-                "%#{maxima}s"
-              else
-                "%#{maxima}s  "
-              end
-            else
-              @formats[index]
-            end
-            sentence << f % column.to_s
+            sentence << format_cell(column, row.size, index)
           end
 
           sentence = truncate(sentence)
+          sentence << "|" if options[:borders]
           stdout.puts sentence
+
         end
+        print_border_separator if options[:borders]
       end
 
     private
 
       def prepare(array)
+        array = array.reject{|row| row == BORDER_SEPARATOR }
+
         @formats << "%-#{@colwidth + 2}s".dup if @colwidth
         start = @colwidth ? 1 : 0
 
         colcount = array.max { |a, b| a.size <=> b.size }.size
 
         start.upto(colcount - 1) do |index|
           maxima = array.map { |row| row[index] ? row[index].to_s.size : 0 }.max
+
           @maximas << maxima
-          @formats << if index == colcount - 1
+          @formats << if options[:borders]
+             "%-#{maxima}s".dup
+          elsif index == colcount - 1
             # Don't output 2 trailing spaces when printing the last column
             "%-s".dup
           else
@@ -64,6 +70,37 @@ def prepare(array)
         @formats << "%s"
       end
 
+      def format_cell(column, row_size, index)
+        maxima = @maximas[index]
+
+        f = if column.is_a?(Numeric)
+          if options[:borders]
+            # With borders we handle padding separately
+            "%#{maxima}s"
+          elsif index == row_size - 1
+            # Don't output 2 trailing spaces when printing the last column
+            "%#{maxima}s"
+          else
+            "%#{maxima}s  "
+          end
+        else
+          @formats[index]
+        end
+
+        cell = "".dup
+        cell << "|" + " " * @padding if options[:borders]
+        cell << f % column.to_s
+        cell << " " * @padding if options[:borders]
+        cell
+      end
+
+      def print_border_separator
+        top = @maximas.map do |maxima|
+          " " * @indent + "+" + "-" * (maxima + 2 * @padding)
+        end
+        stdout.puts top.join + "+"
+      end
+
       def truncate(string)
         return string unless @truncate
         as_unicode do

spec/shell/basic_spec.rb

@@ -432,6 +432,44 @@ def  #456  Lanç...
 Erik  1234567890123  green
       TABLE
     end
+
+    it "prints a table with borders" do
+      content = capture(:stdout) { shell.print_table(@table, borders: true) }
+      expect(content).to eq(<<-TABLE)
++-----+------+-------------+
+| abc | #123 | first three |
+|     | #0   | empty       |
+| xyz | #786 | last three  |
++-----+------+-------------+
+TABLE
+    end
+
+    it "prints a table with borders and separators" do
+      @table.insert(1, :separator)
+      content = capture(:stdout) { shell.print_table(@table, borders: true) }
+      expect(content).to eq(<<-TABLE)
++-----+------+-------------+
+| abc | #123 | first three |
++-----+------+-------------+
+|     | #0   | empty       |
+| xyz | #786 | last three  |
++-----+------+-------------+
+TABLE
+    end
+
+    it "prints a table with borders and small numbers and right-aligns them" do
+      table = [
+        ["Name", "Number", "Color"], # rubocop: disable Style/WordArray
+        ["Erik", 1, "green"]
+      ]
+      content = capture(:stdout) { shell.print_table(table, borders: true) }
+      expect(content).to eq(<<-TABLE)
++------+--------+-------+
+| Name | Number | Color |
+| Erik |      1 | green |
++------+--------+-------+
+TABLE
+    end
   end
 
   describe "#file_collision" do