From 1acbb84444ba40ca106f6bf529a877f39d61ed8a Mon Sep 17 00:00:00 2001
From: Mathias Vorreiter Pedersen <mathiasvp@github.com>
Date: Fri, 5 Apr 2024 11:58:43 +0100
Subject: [PATCH] Shared/Java: Make the 'isNull' interface slightly prettier.

---
 java/ql/lib/semmle/code/java/dataflow/TypeFlow.qll        | 7 ++++---
 shared/typeflow/codeql/typeflow/TypeFlow.qll              | 6 ++++++
 shared/typeflow/codeql/typeflow/internal/TypeFlowImpl.qll | 3 +++
 3 files changed, 13 insertions(+), 3 deletions(-)

diff --git a/java/ql/lib/semmle/code/java/dataflow/TypeFlow.qll b/java/ql/lib/semmle/code/java/dataflow/TypeFlow.qll
index afec2a22ae8..ac781e223f2 100644
--- a/java/ql/lib/semmle/code/java/dataflow/TypeFlow.qll
+++ b/java/ql/lib/semmle/code/java/dataflow/TypeFlow.qll
@@ -133,11 +133,12 @@ private module Input implements TypeFlowInput<J::Location> {
       not decl.hasImplicitInit() and
       not exists(decl.getInit())
     )
-    or
-    forex(TypeFlowNode mid | joinStep(mid, n) | Make<J::Location, Input>::isNull(mid)) and
+  }
+
+  predicate isExcludedFromNullAnalysis(TypeFlowNode n) {
     // Fields that are never assigned a non-null value are probably set by
     // reflection and are thus not always null.
-    not exists(n.asField())
+    exists(n.asField())
   }
 
   predicate exactTypeBase(TypeFlowNode n, RefType t) {
diff --git a/shared/typeflow/codeql/typeflow/TypeFlow.qll b/shared/typeflow/codeql/typeflow/TypeFlow.qll
index d2862b77637..7518805ac56 100644
--- a/shared/typeflow/codeql/typeflow/TypeFlow.qll
+++ b/shared/typeflow/codeql/typeflow/TypeFlow.qll
@@ -42,6 +42,12 @@ signature module TypeFlowInput<LocationSig Location> {
   /** Holds if `n` represents a `null` value. */
   predicate isNullValue(TypeFlowNode n);
 
+  /**
+   * Holds if `n` should be excluded from the set of null values even if
+   * the null analysis determines that `n` is always null.
+   */
+  default predicate isExcludedFromNullAnalysis(TypeFlowNode n) { none() }
+
   /** A type. */
   class Type {
     /** Gets a textual representation of this type. */
diff --git a/shared/typeflow/codeql/typeflow/internal/TypeFlowImpl.qll b/shared/typeflow/codeql/typeflow/internal/TypeFlowImpl.qll
index d640c4b67e1..c06b372afba 100644
--- a/shared/typeflow/codeql/typeflow/internal/TypeFlowImpl.qll
+++ b/shared/typeflow/codeql/typeflow/internal/TypeFlowImpl.qll
@@ -10,6 +10,9 @@ module TypeFlow<LocationSig Location, TypeFlowInput<Location> I> {
     isNullValue(n)
     or
     exists(TypeFlowNode mid | isNull(mid) and step(mid, n))
+    or
+    forex(TypeFlowNode mid | I::joinStep(mid, n) | isNull(mid)) and
+    not isExcludedFromNullAnalysis(n)
   }
 
   /**