Added special location pragma to lexer: #<loc:"filename",line,column> to...

Added special location pragma to lexer: #<loc:"filename",line,column> to override's a lexer's filename/line/column in the middle of tokenization (useful for ecr and other templates)

spec/compiler/lexer/location_spec.cr

@@ -36,4 +36,36 @@ describe "Lexer: location" do
     assert_token_column_number lexer, :NEWLINE, 16
     assert_token_column_number lexer, :NUMBER, 1
   end
+
+  it "overrides location with pragma" do
+    lexer = Lexer.new %(1 + #<loc:"foo",12,34>2)
+    lexer.filename = "bar"
+
+    token = lexer.next_token
+    token.type.should eq(:NUMBER)
+    token.line_number.should eq(1)
+    token.column_number.should eq(1)
+    token.filename.should eq("bar")
+
+    token = lexer.next_token
+    token.type.should eq(:SPACE)
+    token.line_number.should eq(1)
+    token.column_number.should eq(2)
+
+    token = lexer.next_token
+    token.type.should eq(:"+")
+    token.line_number.should eq(1)
+    token.column_number.should eq(3)
+
+    token = lexer.next_token
+    token.type.should eq(:SPACE)
+    token.line_number.should eq(1)
+    token.column_number.should eq(4)
+
+    token = lexer.next_token
+    token.type.should eq(:NUMBER)
+    token.line_number.should eq(12)
+    token.column_number.should eq(34)
+    token.filename.should eq("foo")
+  end
 end

src/compiler/crystal/lexer.cr

@@ -37,8 +37,20 @@ module Crystal
       # Skip comments
       if current_char == '#'
         char = next_char_no_column_increment
-        while char != '\n' && char != '0'
-          char = next_char_no_column_increment
+
+        # Check #<loc:"file",line,column> pragma comment
+        if char == '<' &&
+          (char = next_char_no_column_increment) == 'l' &&
+          (char = next_char_no_column_increment) == 'o' &&
+          (char = next_char_no_column_increment) == 'c' &&
+          (char = next_char_no_column_increment) == ':' &&
+          (char = next_char_no_column_increment) == '"'
+          next_char_no_column_increment
+          consume_loc_pragma
+        else
+          while char != '\n' && char != '0'
+            char = next_char_no_column_increment
+          end
         end
       end
 
@@ -1557,6 +1569,63 @@ module Crystal
       @token
     end
 
+    def consume_loc_pragma
+      filename_pos = current_pos
+
+      while true
+        case current_char
+        when '"'
+          break
+        when '0'
+          raise "unexpected end of file in loc pragma"
+        else
+          next_char_no_column_increment
+        end
+      end
+
+      filename = string_range(filename_pos)
+
+      # skip '"'
+      next_char
+
+      unless current_char == ','
+        raise "expected ',' in loc pragma after filename"
+      end
+      next_char
+
+      line_number = 0
+      while true
+        case current_char
+        when '0' .. '9'
+          line_number = 10 * line_number + (current_char - '0').to_i
+        when ','
+          next_char
+          break
+        else
+          raise "expected digit or ',' in loc pragma for line number"
+        end
+        next_char
+      end
+
+      column_number = 0
+      while true
+        case current_char
+        when '0' .. '9'
+          column_number = 10 * column_number + (current_char - '0').to_i
+        when '>'
+          next_char
+          break
+        else
+          raise "expected digit or '>' in loc pragma for column_number number"
+        end
+        next_char
+      end
+
+      @token.filename = @filename = filename
+      @token.line_number = @line_number = line_number
+      @token.column_number = @column_number = column_number
+    end
+
     def next_char_no_column_increment
       @reader.next_char
     end