compiler, cli: Support Nice Compilation Error Messages

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

Sources/Common/Error.swift

@@ -39,7 +39,29 @@ public struct Error: Errorable, Equatable, CustomStringConvertible {
   }
 }
 
+extension String {
+  public func trimmingPostfix(_ in_: String.Element) -> String {
+    return String(self.reversed().drop { $0 == in_ }.reversed())
+  }
+}
+
 public struct ErrorWithLocation: Errorable, Equatable, CustomStringConvertible {
+
+  public func format(_ formatter: any Formattable, _ sc: SourceCode) -> String {
+    guard let (fp, source, prior, after) = sc.getSourceSnippet(location: self.location, context: 5)
+    else {
+      return self.format(formatter)
+    }
+
+    let prior_snipped = prior.trimmingPrefix(["\n"])
+    let after_snipped = after.prefix { $0 != "\n" }
+    return formatter.formatWithStyle("Error: ", Style(StyleColor.Red))
+      + "In \(fp), there was an error: \n..." + prior_snipped
+      + formatter.formatWithStyle(source, Style(.none, [StyleFormat.Underline])) + after_snipped
+      + "...\n"
+      + self._msg
+  }
+
   public func format(_ formatter: any Formattable) -> String {
     let bold_red = Style(StyleColor.Red, [StyleFormat.Bold])
     let formatted_location = formatter.formatWithStyle(self.location.description, bold_red)