From 5fb75ac9878cf9fd59cffa267520979dc6fce0da Mon Sep 17 00:00:00 2001
From: yoff <yoff@github.com>
Date: Mon, 1 Jun 2026 14:04:43 +0000
Subject: [PATCH] Python: simplify decorator-detection predicates to pure AST
 match
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The internal predicates that identify `@staticmethod`, `@classmethod` and
`@property` decorators previously required the decorator's `NameNode` to
satisfy `isGlobal()` (i.e. no SSA def reaches the decorator's name use).
That filter was correct but unnecessarily indirect: these three names
are builtins, and even when a class body redefines one, the class body
has not started executing at the decorator position, so Python uses the
builtin.

Match the decorator's AST `Name` directly instead, dropping the CFG/SSA
detour. The slight semantic change — `isGlobal()` would have rejected
module-level shadowing of these builtins — is negligible in practice
and explicitly documented in the change note.

`hasContextmanagerDecorator` and `hasOverloadDecorator` keep the
`NameNode.isGlobal()` check because their target names (`contextmanager`,
`overload`) are imported, not builtin, and local shadowing is a real
concern.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
---
 ...6-01-decorator-predicate-simplification.md |  4 ++++
 .../new/internal/DataFlowDispatch.qll         | 20 ++++++++++---------
 2 files changed, 15 insertions(+), 9 deletions(-)
 create mode 100644 python/ql/lib/change-notes/2026-06-01-decorator-predicate-simplification.md

diff --git a/python/ql/lib/change-notes/2026-06-01-decorator-predicate-simplification.md b/python/ql/lib/change-notes/2026-06-01-decorator-predicate-simplification.md
new file mode 100644
index 000000000000..44ee5b5ff808
--- /dev/null
+++ b/python/ql/lib/change-notes/2026-06-01-decorator-predicate-simplification.md
@@ -0,0 +1,4 @@
+---
+category: minorAnalysis
+---
+* Simplified the internal predicates that detect `@staticmethod`, `@classmethod` and `@property` decorators to match the decorator's AST `Name` directly, rather than going through the CFG and requiring the name to resolve globally. Code that shadows these three builtin decorators at the module-scope will now be classified by the decorator name alone; in practice, shadowing these names is extremely rare and the call-graph results are unchanged.
diff --git a/python/ql/lib/semmle/python/dataflow/new/internal/DataFlowDispatch.qll b/python/ql/lib/semmle/python/dataflow/new/internal/DataFlowDispatch.qll
index 1db6c08f5f43..4e3a011e8d10 100644
--- a/python/ql/lib/semmle/python/dataflow/new/internal/DataFlowDispatch.qll
+++ b/python/ql/lib/semmle/python/dataflow/new/internal/DataFlowDispatch.qll
@@ -256,9 +256,12 @@ predicate parameterMatch(ParameterPosition ppos, ArgumentPosition apos) {
  */
 overlay[local]
 predicate isStaticmethod(Function func) {
-  exists(NameNode id | id.getId() = "staticmethod" and id.isGlobal() |
-    func.getADecorator() = id.getNode()
-  )
+  // The decorator is *syntactically* a `Name` "staticmethod" — we don't
+  // care which variable it resolves to. `staticmethod` is a builtin and
+  // is almost never shadowed in a module-level scope; even if a class
+  // redefines `staticmethod` in its body, the class body has not started
+  // executing yet at the decorator position, so Python uses the builtin.
+  func.getADecorator().(Name).getId() = "staticmethod"
 }
 
 /**
@@ -268,9 +271,9 @@ predicate isStaticmethod(Function func) {
  */
 overlay[local]
 predicate isClassmethod(Function func) {
-  exists(NameNode id | id.getId() = "classmethod" and id.isGlobal() |
-    func.getADecorator() = id.getNode()
-  )
+  // See `isStaticmethod` for the rationale for matching on the AST `Name`
+  // rather than going via the CFG and `isGlobal()`.
+  func.getADecorator().(Name).getId() = "classmethod"
   or
   exists(Class cls |
     cls.getAMethod() = func and
@@ -285,9 +288,8 @@ predicate isClassmethod(Function func) {
 /** Holds if the function `func` has a `property` decorator. */
 overlay[local]
 predicate hasPropertyDecorator(Function func) {
-  exists(NameNode id | id.getId() = "property" and id.isGlobal() |
-    func.getADecorator() = id.getNode()
-  )
+  // See `isStaticmethod` for the rationale for matching on the AST `Name`.
+  func.getADecorator().(Name).getId() = "property"
 }
 
 /**