Function getProjectRelativePath

packages/compiler-cli/src/ngtsc/util/src/path.ts:29–48

(
  fileName: string,
  rootDirs: readonly string[],
  compilerHost: Pick<ts.CompilerHost, 'getCanonicalFileName'>,
)

 * @returns
 */
export function getProjectRelativePath(
  fileName: string,
  rootDirs: readonly string[],
  compilerHost: Pick<ts.CompilerHost, 'getCanonicalFileName'>,
): string | null {
  // Note: we need to pass both the file name and the root directories through getCanonicalFileName,
  // because the root directories might've been passed through it already while the source files
  // definitely have not. This can break the relative return value, because in some platforms
  // getCanonicalFileName lowercases the path.
  const filePath = compilerHost.getCanonicalFileName(fileName);

  for (const rootDir of rootDirs) {
    const rel = relative(compilerHost.getCanonicalFileName(rootDir), filePath);
    if (!rel.startsWith('..')) {
      return rel;
    }
  }

  return null;
}