From 8e6b168730266552a46f51968213637f0e4d539a Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Thu, 23 Jul 2026 10:15:43 +0000
Subject: [PATCH] C++: Remove lookbehind assertions

---
 .../semmle/code/cpp/regex/RegexTreeView.qll   | 36 ++-------------
 .../code/cpp/regex/internal/ParseRegExp.qll   | 46 +------------------
 2 files changed, 4 insertions(+), 78 deletions(-)

diff --git a/cpp/ql/lib/semmle/code/cpp/regex/RegexTreeView.qll b/cpp/ql/lib/semmle/code/cpp/regex/RegexTreeView.qll
index 939038dd722..8eef64c9dc0 100644
--- a/cpp/ql/lib/semmle/code/cpp/regex/RegexTreeView.qll
+++ b/cpp/ql/lib/semmle/code/cpp/regex/RegexTreeView.qll
@@ -991,15 +991,13 @@ private module Impl implements RegexTreeViewSig {
   }
 
   /**
-   * A zero-width lookahead or lookbehind assertion.
+   * A zero-width lookahead assertion.
    *
    * Examples:
    *
    * ```
    * (?=\w)
    * (?!\n)
-   * (?<=\.)
-   * (?<!\\)
    * ```
    */
   class RegExpSubPattern extends RegExpZeroWidthMatch {
@@ -1061,44 +1059,16 @@ private module Impl implements RegexTreeViewSig {
     override string getAPrimaryQlClass() { result = "RegExpNegativeLookahead" }
   }
 
-  /**
-   * A zero-width lookbehind assertion.
-   *
-   * Examples:
-   *
-   * ```
-   * (?<=\.)
-   * (?<!\\)
-   * ```
-   */
   abstract class RegExpLookbehind extends RegExpSubPattern { }
 
-  /**
-   * A positive-lookbehind assertion.
-   *
-   * Examples:
-   *
-   * ```
-   * (?<=\.)
-   * ```
-   */
   class RegExpPositiveLookbehind extends RegExpLookbehind {
-    RegExpPositiveLookbehind() { re.positiveLookbehindAssertionGroup(start, end) }
+    RegExpPositiveLookbehind() { none() }
 
     override string getAPrimaryQlClass() { result = "RegExpPositiveLookbehind" }
   }
 
-  /**
-   * A negative-lookbehind assertion.
-   *
-   * Examples:
-   *
-   * ```
-   * (?<!\\)
-   * ```
-   */
   additional class RegExpNegativeLookbehind extends RegExpLookbehind {
-    RegExpNegativeLookbehind() { re.negativeLookbehindAssertionGroup(start, end) }
+    RegExpNegativeLookbehind() { none() }
 
     override string getAPrimaryQlClass() { result = "RegExpNegativeLookbehind" }
   }
diff --git a/cpp/ql/lib/semmle/code/cpp/regex/internal/ParseRegExp.qll b/cpp/ql/lib/semmle/code/cpp/regex/internal/ParseRegExp.qll
index baa8d6c3556..c84091b063f 100644
--- a/cpp/ql/lib/semmle/code/cpp/regex/internal/ParseRegExp.qll
+++ b/cpp/ql/lib/semmle/code/cpp/regex/internal/ParseRegExp.qll
@@ -510,8 +510,6 @@ abstract class RegExp extends StringLiteral {
     this.negativeAssertionGroup(start, end)
     or
     this.positiveLookaheadAssertionGroup(start, end)
-    or
-    this.positiveLookbehindAssertionGroup(start, end)
   }
 
   /** Holds if an empty group is found between `start` and `end`. */
@@ -534,16 +532,10 @@ abstract class RegExp extends StringLiteral {
     this.emptyGroup(start, end)
     or
     this.negativeAssertionGroup(start, end)
-    or
-    this.positiveLookbehindAssertionGroup(start, end)
   }
 
   private predicate negativeAssertionGroup(int start, int end) {
-    exists(int inStart |
-      this.negativeLookaheadAssertionStart(start, inStart)
-      or
-      this.negativeLookbehindAssertionStart(start, inStart)
-    |
+    exists(int inStart | this.negativeLookaheadAssertionStart(start, inStart) |
       this.groupContents(start, end, inStart, _)
     )
   }
@@ -555,13 +547,6 @@ abstract class RegExp extends StringLiteral {
     )
   }
 
-  /** Holds if a negative lookbehind is found between `start` and `end` */
-  predicate negativeLookbehindAssertionGroup(int start, int end) {
-    exists(int inStart | this.negativeLookbehindAssertionStart(start, inStart) |
-      this.groupContents(start, end, inStart, _)
-    )
-  }
-
   /** Holds if a positive lookahead is found between `start` and `end` */
   predicate positiveLookaheadAssertionGroup(int start, int end) {
     exists(int inStart | this.lookaheadAssertionStart(start, inStart) |
@@ -569,13 +554,6 @@ abstract class RegExp extends StringLiteral {
     )
   }
 
-  /** Holds if a positive lookbehind is found between `start` and `end` */
-  predicate positiveLookbehindAssertionGroup(int start, int end) {
-    exists(int inStart | this.lookbehindAssertionStart(start, inStart) |
-      this.groupContents(start, end, inStart, _)
-    )
-  }
-
   private predicate groupStart(int start, int end) {
     this.nonCapturingGroupStart(start, end)
     or
@@ -583,10 +561,6 @@ abstract class RegExp extends StringLiteral {
     or
     this.negativeLookaheadAssertionStart(start, end)
     or
-    this.lookbehindAssertionStart(start, end)
-    or
-    this.negativeLookbehindAssertionStart(start, end)
-    or
     this.simpleGroupStart(start, end)
   }
 
@@ -621,24 +595,6 @@ abstract class RegExp extends StringLiteral {
     end = start + 3
   }
 
-  /** Matches the start of a positive lookbehind assertion, i.e. `(?<=`. */
-  private predicate lookbehindAssertionStart(int start, int end) {
-    this.isGroupStart(start) and
-    this.getChar(start + 1) = "?" and
-    this.getChar(start + 2) = "<" and
-    this.getChar(start + 3) = "=" and
-    end = start + 4
-  }
-
-  /** Matches the start of a negative lookbehind assertion, i.e. `(?<!`. */
-  private predicate negativeLookbehindAssertionStart(int start, int end) {
-    this.isGroupStart(start) and
-    this.getChar(start + 1) = "?" and
-    this.getChar(start + 2) = "<" and
-    this.getChar(start + 3) = "!" and
-    end = start + 4
-  }
-
   /** Matches the contents of a group. */
   predicate groupContents(int start, int end, int inStart, int inEnd) {
     this.groupStart(start, inStart) and