1. A system comprising: at least one processor: and a memory connected to the at least one processor; wherein the at least one processor is configured to: generate suggestions to correct an error comprising an undefined token in program source code by using an include graph for a project, wherein the include graph includes a plurality of nodes, a node represents a file associated with the project, wherein a project includes a collection of files needed to generate an executable of the program source code, the suggestions generated by traversing the include graph to find all paths going from a node representing a file in which the undefined token is found to a project node, wherein each traversed path is segmented based on a folder in which a node resides; and display a topmost file in each directory associated with a folder that includes an external file having a definition for the undefined token as a suggestion to correct the error, wherein the external file is external to the project.