compiler: Add Ability to Annotate Preprocessed Source

Signed-off-by: Will Hawkins <hawkinsw@obs.cr>

Sources/Common/SourceCode.swift

@@ -143,14 +143,57 @@ public struct SourceCode {
     self.locations = locations
   }
 
-  public func getSource() -> String {
-    return self.code
-  }
-
   public func getManager() -> SourceManager {
     return self.manager
   }
 
+  static func do_annotate(
+    _ contents: String, _ manager: SourceManager, _ locations: FileSourceLocation,
+    _ formatter: Formattable, _ style: Style
+  ) -> String {
+    var result = ""
+
+    // Keep track of the start of any gap between nested locations.
+    var gap_start = contents.startIndex
+
+    // contents are devoid of any preceding source code, but the locations do not know that. So,
+    // when we use a range from locations we must adjust appropriately.
+    let offset = locations.location.range.lowerBound
+
+    for nested in locations.getNestedLocations() {
+      let nested_start = contents.index(
+        contents.startIndex, offsetBy: nested.location.range.lowerBound - offset)
+      let nested_end = contents.index(
+        contents.startIndex, offsetBy: nested.location.range.upperBound - offset)
+
+      // Add in any gap.
+      result += contents[gap_start..<nested_start]
+
+      // Handle this range (recursively)
+      result += do_annotate(
+        "\(contents[nested_start ..< nested_end])", manager, nested, formatter, style)
+
+      // Adjust where the next gap will start.
+      gap_start = nested_end
+    }
+
+    // Is there anything left?
+    let remainder = contents[gap_start...]
+
+    return formatter.formatWithStyle(result + remainder, style)
+  }
+
+  public func getSource(
+    annotated: Bool = false, formatter: Formattable = FormatterDelimited("<", ">"),
+    initialStyle: Style = Style(StyleColor.Red)
+  ) -> String {
+    if annotated {
+      return SourceCode.do_annotate(
+        self.code, self.manager, self.locations, formatter, initialStyle)
+    }
+    return self.code
+  }
+
   public func getLocations() -> FileSourceLocation {
     return self.locations
   }