JavaScript: Move getAMatchedConstant(RegExpTerm) into the library.

javascript/ql/src/Security/CWE-116/IncompleteSanitization.ql

@@ -21,24 +21,11 @@ string metachar() { result = "'\"\\&<>\n\r\t*|{}[]%$".charAt(_) }
 
 /** Gets a string matched by `e` in a `replace` call. */
 string getAMatchedString(Expr e) {
-  result = getAMatchedConstant(e.(RegExpLiteral).getRoot()).getValue()
+  result = e.(RegExpLiteral).getRoot().getAMatchedString()
   or
   result = e.getStringValue()
 }
 
-/** Gets a constant matched by `t`. */
-RegExpConstant getAMatchedConstant(RegExpTerm t) {
-  result = t
-  or
-  result = getAMatchedConstant(t.(RegExpAlt).getAlternative())
-  or
-  result = getAMatchedConstant(t.(RegExpGroup).getAChild())
-  or
-  exists(RegExpCharacterClass recc | recc = t and not recc.isInverted() |
-    result = getAMatchedConstant(recc.getAChild())
-  )
-}
-
 /** Holds if `t` is simple, that is, a union of constants. */
 predicate isSimple(RegExpTerm t) {
   t instanceof RegExpConstant

javascript/ql/src/semmle/javascript/Regexp.qll

@@ -185,6 +185,11 @@ class RegExpTerm extends Locatable, @regexpterm {
    * into account.
    */
   string getConstantValue() { none() }
+
+  /**
+   * Gets a string that is matched by this regular-expression term.
+   */
+  string getAMatchedString() { result = getConstantValue() }
 }
 
 /**
@@ -280,6 +285,8 @@ class RegExpAlt extends RegExpTerm, @regexp_alt {
   int getNumAlternative() { result = getNumChild() }
 
   override predicate isNullable() { getAlternative().isNullable() }
+
+  override string getAMatchedString() { result = getAlternative().getAMatchedString() }
 }
 
 /**
@@ -574,6 +581,8 @@ class RegExpGroup extends RegExpTerm, @regexp_group {
   override predicate isNullable() { getAChild().isNullable() }
 
   override string getConstantValue() { result = getAChild().getConstantValue() }
+
+  override string getAMatchedString() { result = getAChild().getAMatchedString() }
 }
 
 /**
@@ -759,6 +768,10 @@ class RegExpCharacterClass extends RegExpTerm, @regexp_char_class {
   predicate isInverted() { isInverted(this) }
 
   override predicate isNullable() { none() }
+
+  override string getAMatchedString() {
+    not isInverted() and result = getAChild().getAMatchedString()
+  }
 }
 
 /**