compiler: Support Querying For Files In Preprocessed Code

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

Sources/Common/SourceCode.swift

@@ -129,6 +129,22 @@ public struct FileSourceLocation: Equatable, CustomStringConvertible {
         return "\(location)"
       }).joined(separator: ",") + ")"
   }
+
+  public func pathForLocation(_ location: Int) -> FilePath? {
+
+    let queried_location = SourceLocation(location, 1)
+    if !self.location.contains(queried_location) {
+      return .none
+    }
+
+    for nested in self.nested {
+      if nested.location.contains(queried_location) {
+        return nested.pathForLocation(location)
+      }
+    }
+
+    return self.getPath()
+  }
 }
 
 /// Represent preprocessed P4 code.
@@ -197,6 +213,10 @@ public struct SourceCode {
   public func getLocations() -> FileSourceLocation {
     return self.locations
   }
+
+  public func pathForLocation(_ location: Int) -> FilePath? {
+    return self.locations.pathForLocation(location)
+  }
 }
 
 func do_preprocess(