Swift: Implement getExtension and getStem

Author: hvitved

swift/ql/lib/codeql/swift/elements/File.qll

@@ -15,11 +15,64 @@ class File extends Generated::File {
   /** Gets the URL of this file. */
   string getURL() { result = "file://" + this.getAbsolutePath() + ":0:0:0:0" }
 
-  /** Gets the base name of this file. */
-  string getBaseName() {
-    result = this.getAbsolutePath().regexpCapture(".*/(([^/]*?)(?:\\.([^.]*))?)", 1)
+  /**
+   * Holds if either,
+   * - `part` is the base name of this container and `i = 1`, or
+   * - `part` is the stem of this container and `i = 2`, or
+   * - `part` is the extension of this container and `i = 3`.
+   */
+  cached
+  private predicate splitAbsolutePath(string part, int i) {
+    part = this.getAbsolutePath().regexpCapture(".*/(([^/]*?)(?:\\.([^.]*))?)", i)
   }
 
+  /** Gets the base name of this file. */
+  string getBaseName() { this.splitAbsolutePath(result, 1) }
+
+  /**
+   * Gets the extension of this container, that is, the suffix of its base name
+   * after the last dot character, if any.
+   *
+   * In particular,
+   *
+   *  - if the name does not include a dot, there is no extension, so this
+   *    predicate has no result;
+   *  - if the name ends in a dot, the extension is the empty string;
+   *  - if the name contains multiple dots, the extension follows the last dot.
+   *
+   * Here are some examples of absolute paths and the corresponding extensions
+   * (surrounded with quotes to avoid ambiguity):
+   *
+   * <table border="1">
+   * <tr><th>Absolute path</th><th>Extension</th></tr>
+   * <tr><td>"/tmp/tst.txt"</td><td>"txt"</td></tr>
+   * <tr><td>"/tmp/.classpath"</td><td>"classpath"</td></tr>
+   * <tr><td>"/bin/bash"</td><td>not defined</td></tr>
+   * <tr><td>"/tmp/tst2."</td><td>""</td></tr>
+   * <tr><td>"/tmp/x.tar.gz"</td><td>"gz"</td></tr>
+   * </table>
+   */
+  string getExtension() { this.splitAbsolutePath(result, 3) }
+
+  /**
+   * Gets the stem of this container, that is, the prefix of its base name up to
+   * (but not including) the last dot character if there is one, or the entire
+   * base name if there is not.
+   *
+   * Here are some examples of absolute paths and the corresponding stems
+   * (surrounded with quotes to avoid ambiguity):
+   *
+   * <table border="1">
+   * <tr><th>Absolute path</th><th>Stem</th></tr>
+   * <tr><td>"/tmp/tst.txt"</td><td>"tst"</td></tr>
+   * <tr><td>"/tmp/.classpath"</td><td>""</td></tr>
+   * <tr><td>"/bin/bash"</td><td>"bash"</td></tr>
+   * <tr><td>"/tmp/tst2."</td><td>"tst2"</td></tr>
+   * <tr><td>"/tmp/x.tar.gz"</td><td>"x.tar"</td></tr>
+   * </table>
+   */
+  string getStem() { this.splitAbsolutePath(result, 2) }
+
   /**
    * Gets the number of lines containing code in this file. This value
    * is approximate.