Revert "Revert "Python: switch to shared implementation of IncompleteHostnameRegExp.ql""

This reverts commit 6d24591416.

python/ql/lib/semmle/python/RegexTreeView.qll

@@ -2,6 +2,7 @@
 
 import python
 private import semmle.python.regex
+private import semmle.python.dataflow.new.DataFlow
 
 /**
  * An element containing a regular expression term, that is, either
@@ -48,6 +49,19 @@ newtype TRegExpParent =
   /** A back reference */
   TRegExpBackRef(Regex re, int start, int end) { re.backreference(start, end) }
 
+/**
+ * Provides utility predicates related to regular expressions.
+ */
+module RegExpPatterns {
+  /**
+   * Gets a pattern that matches common top-level domain names in lower case.
+   */
+  string getACommonTld() {
+    // according to ranking by http://google.com/search?q=site:.<<TLD>>
+    result = "(?:com|org|edu|gov|uk|net|io)(?![a-z0-9])"
+  }
+}
+
 /**
  * An element containing a regular expression term, that is, either
  * a string literal (parsed as a regular expression)
@@ -445,6 +459,8 @@ class RegExpAlt extends RegExpTerm, TRegExpAlt {
   override string getPrimaryQLClass() { result = "RegExpAlt" }
 }
 
+class RegExpCharEscape = RegExpEscape;
+
 /**
  * An escaped regular expression term, that is, a regular expression
  * term starting with a backslash, which is not a backreference.
@@ -751,6 +767,9 @@ class RegExpGroup extends RegExpTerm, TRegExpGroup {
    */
   int getNumber() { result = re.getGroupNumber(start, end) }
 
+  /** Holds if this is a capture group. */
+  predicate isCapture() { exists(this.getNumber()) }
+
   /** Holds if this is a named capture group. */
   predicate isNamed() { exists(this.getName()) }
 
@@ -1009,3 +1028,24 @@ class RegExpBackRef extends RegExpTerm, TRegExpBackRef {
 
 /** Gets the parse tree resulting from parsing `re`, if such has been constructed. */
 RegExpTerm getParsedRegExp(StrConst re) { result.getRegex() = re and result.isRootTerm() }
+
+/**
+ * A node whose value may flow to a position where it is interpreted
+ * as a part of a regular expression.
+ */
+class RegExpPatternSource extends DataFlow::CfgNode {
+  private Regex astNode;
+
+  RegExpPatternSource() { astNode = this.asExpr() }
+
+  /**
+   * Gets a node where the pattern of this node is parsed as a part of
+   * a regular expression.
+   */
+  DataFlow::Node getAParse() { result = this }
+
+  /**
+   * Gets the root term of the regular expression parsed from this pattern.
+   */
+  RegExpTerm getRegExpTerm() { result.getRegex() = astNode }
+}