Apply suggestions from code review

Co-authored-by: yoff <lerchedahl@gmail.com>

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

@@ -40,7 +40,7 @@ newtype TRegExpParent =
   TRegExpSpecialChar(Regex re, int start, int end) { re.specialCharacter(start, end, _) } or
   /** A normal character */
   TRegExpNormalChar(Regex re, int start, int end) {
-    re.normalCharacterSequence(start, end)
+    re.simpleCharacterSequence(start, end)
     or
     re.escapedCharacter(start, end) and
     not re.specialCharacter(start, end, _)

python/ql/lib/semmle/python/regex.qll

@@ -447,18 +447,22 @@ abstract class RegexString extends Expr {
   }
 
   /**
-   * A sequence of 'normal' characters.
+   * A sequence of 'simple' characters.
    */
-  predicate normalCharacterSequence(int start, int end) {
-    this.normalCharacter(start, end) and
-    end = start + 1 and
-    exists(int x, int y | this.charSet(x, y) and x <= start and y >= end)
+  predicate simpleCharacterSequence(int start, int end) {
+    // a simple character inside a character set is interpreted on its own
+    this.simpleCharacter(start, end) and
+    this.inCharSet(start)
     or
+    // a maximal run of simple characters is considered as one constant
     exists(int s, int e |
-      e = max(int i | normalCharacterSub(s, i)) and
-      not exists(int x, int y | this.charSet(x, y) and x <= s and y >= e)
+      e = max(int i | simpleCharacterRun(s, i)) and
+      not this.inCharSet(s)
     |
-      if qualifier(e, _, _, _)
+      // 'abc' can be considered one constant, but
+      // 'abc+' has to be broken up into 'ab' and 'c+',
+      // as the qualifier only applies to 'c'.
+      if this.qualifier(e, _, _, _)
       then
         end = e and start = e - 1
         or
@@ -470,17 +474,17 @@ abstract class RegexString extends Expr {
     )
   }
 
-  private predicate normalCharacterSub(int start, int end) {
+  private predicate simpleCharacterRun(int start, int end) {
     (
-      normalCharacterSub(start, end - 1)
+      simpleCharacterRun(start, end - 1)
       or
       start = end - 1 and not normalCharacter(start - 1, start)
     ) and
-    this.normalCharacter(end - 1, end)
+    this.simpleCharacter(end - 1, end)
   }
 
   private predicate characterItem(int start, int end) {
-    this.normalCharacterSequence(start, end) or
+    this.simpleCharacterSequence(start, end) or
     this.escapedCharacter(start, end) or
     this.specialCharacter(start, end, _)
   }