Show parsing errors with line and column number

lib/slime.ex

@@ -9,7 +9,16 @@ defmodule Slime do
     @moduledoc """
     Syntax exception which may appear during parsing and compilation processes
     """
-    defexception message: "Syntax error in slime file"
+    defexception [:line, :line_number, :column, message: "Syntax error", source: "INPUT"]
+
+    def message(exception) do
+      """
+      #{exception.message}
+      #{exception.source}, Line #{exception.line_number}, Column #{exception.column}
+      #{exception.line}
+      #{String.duplicate(" ", exception.column - 1)}^
+      """
+    end
   end
 
   defdelegate render(slime),           to: Renderer

lib/slime/parser.ex

@@ -13,13 +13,27 @@ defmodule Slime.Parser do
   def parse(input) do
     indented_input = Preprocessor.indent(input)
     case :slime_parser.parse(indented_input) do
-      # TODO: Map column index to original input, handle errors on indent and dedent
-      {:fail, error} ->
-        raise TemplateSyntaxError, "Parsing Error: #{inspect error}\n#{input}"
+      {:fail, error} -> handle_syntax_error(input, indented_input, error)
       tokens -> tokens
     end
   end
 
+  defp handle_syntax_error(input, indented_input, error) do
+    {_reason, error, {{:line, line}, {:column, column}}} = error
+    indented_line = indented_input |> String.split("\n") |> Enum.at(line - 1)
+    input_line = input |> String.split("\n") |> Enum.at(line - 1)
+    indent = Preprocessor.indent_meta_symbol
+    column = case indented_line do
+      <<^indent::binary-size(1), _::binary>> -> column - 1
+      _ -> column
+    end
+    raise TemplateSyntaxError,
+      line: input_line,
+      message: inspect(error),
+      line_number: line,
+      column: column
+  end
+
   @content  "|"
   @comment  "/"
   @html     "<"

lib/slime/parser/preprocessor.ex

@@ -2,19 +2,7 @@ defmodule Slime.Parser.Preprocessor do
   @moduledoc """
   This module helps to process input and insert indents and dedents to simplify parser design.
   """
-
-  defmodule IndentationError do
-    defexception [:line, :line_number, :indent, message: "Malformed indentation"]
-
-    def message(exception) do
-      """
-      #{exception.message}
-      INPUT, Line #{exception.line_number}, Column #{exception.indent}
-      #{exception.line}
-      #{String.duplicate(" ", exception.indent)}^
-      """
-    end
-  end
+  alias Slime.TemplateSyntaxError
 
   @indent "\x0E"
   @dedent "\x0F"
@@ -62,7 +50,11 @@ defmodule Slime.Parser.Preprocessor do
           [prev_line | result] = result
           {stack, [line, prev_line <> dedents | result]}
         else
-          raise IndentationError, line: line, line_number: Enum.count(result) + 1, indent: indent
+          raise TemplateSyntaxError,
+            message: "Malformed indentation",
+            line: line,
+            line_number: Enum.count(result) + 1,
+            column: indent
         end
     end
 

test/parser/preprocessor_test.exs

@@ -1,7 +1,7 @@
 defmodule Slime.Parser.PreprocessorTest do
   use ExUnit.Case
   alias Slime.Parser.Preprocessor
-  alias Preprocessor.IndentationError
+  alias Slime.TemplateSyntaxError
 
   doctest Preprocessor
 
@@ -16,7 +16,7 @@ defmodule Slime.Parser.PreprocessorTest do
         | test
     """
 
-    assert_raise(IndentationError, fn -> Preprocessor.indent(slime) end)
+    assert_raise(TemplateSyntaxError, fn -> Preprocessor.indent(slime) end)
   end
 
   test "skip indents in embedded engine lines" do