Python: Remove points-to dependency from parts of SSA

For whatever reason, the CFG node for exceptions and exception groups
was placed with the points-to code. (Probably because a lot of the
predicates depended on points-to.)

However, as it turned out, two of the SSA modules only depended on
non-points-to properties of these nodes, and so it was fairly
straightforward to remove the imports of `LegacyPointsTo` for those
modules.

In the process, I moved the aforementioned CFG node types into
`Flow.qll`, and changed the classes in the `Exceptions` module to the
`...WithPointsTo` form that we introduced elsewhere.

python/ql/lib/semmle/python/Flow.qll

@@ -883,6 +883,58 @@ class StarredNode extends ControlFlowNode {
   ControlFlowNode getValue() { toAst(result) = toAst(this).(Starred).getValue() }
 }
 
+/** The ControlFlowNode for an 'except' statement. */
+class ExceptFlowNode extends ControlFlowNode {
+  ExceptFlowNode() { this.getNode() instanceof ExceptStmt }
+
+  /**
+   * Gets the type handled by this exception handler.
+   * `ExceptionType` in `except ExceptionType as e:`
+   */
+  ControlFlowNode getType() {
+    exists(ExceptStmt ex |
+      this.getBasicBlock().dominates(result.getBasicBlock()) and
+      ex = this.getNode() and
+      result = ex.getType().getAFlowNode()
+    )
+  }
+
+  /**
+   * Gets the name assigned to the handled exception, if any.
+   * `e` in `except ExceptionType as e:`
+   */
+  ControlFlowNode getName() {
+    exists(ExceptStmt ex |
+      this.getBasicBlock().dominates(result.getBasicBlock()) and
+      ex = this.getNode() and
+      result = ex.getName().getAFlowNode()
+    )
+  }
+}
+
+/** The ControlFlowNode for an 'except*' statement. */
+class ExceptGroupFlowNode extends ControlFlowNode {
+  ExceptGroupFlowNode() { this.getNode() instanceof ExceptGroupStmt }
+
+  /**
+   * Gets the type handled by this exception handler.
+   * `ExceptionType` in `except* ExceptionType as e:`
+   */
+  ControlFlowNode getType() {
+    this.getBasicBlock().dominates(result.getBasicBlock()) and
+    result = this.getNode().(ExceptGroupStmt).getType().getAFlowNode()
+  }
+
+  /**
+   * Gets the name assigned to the handled exception, if any.
+   * `e` in `except* ExceptionType as e:`
+   */
+  ControlFlowNode getName() {
+    this.getBasicBlock().dominates(result.getBasicBlock()) and
+    result = this.getNode().(ExceptGroupStmt).getName().getAFlowNode()
+  }
+}
+
 private module Scopes {
   private predicate fast_local(NameNode n) {
     exists(FastLocalVariable v |

python/ql/lib/semmle/python/essa/Essa.qll

@@ -6,7 +6,6 @@ import python
 private import SsaCompute
 import semmle.python.essa.Definitions
 private import semmle.python.internal.CachedStages
-private import LegacyPointsTo
 private import semmle.python.essa.SsaDefinitions
 
 /** An (enhanced) SSA variable derived from `SsaSourceVariable`. */

python/ql/lib/semmle/python/essa/SsaDefinitions.qll

@@ -5,7 +5,6 @@
 
 import python
 private import semmle.python.internal.CachedStages
-private import LegacyPointsTo
 
 /** Hold if `expr` is a test (a branch) and `use` is within that test */
 predicate test_contains(ControlFlowNode expr, ControlFlowNode use) {

python/ql/lib/semmle/python/types/Exceptions.qll

@@ -80,7 +80,7 @@ class RaisingNode extends ControlFlowNode {
       or
       this.getNode() instanceof Print and result = theIOErrorType()
       or
-      exists(ExceptFlowNode except |
+      exists(ExceptFlowNodeWithPointsTo except |
         except = this.getAnExceptionalSuccessor() and
         except.handles_objectapi(result) and
         result = this.innateException_objectapi()
@@ -107,7 +107,7 @@ class RaisingNode extends ControlFlowNode {
       or
       this.getNode() instanceof Print and result = ClassValue::ioError()
       or
-      exists(ExceptFlowNode except |
+      exists(ExceptFlowNodeWithPointsTo except |
         except = this.getAnExceptionalSuccessor() and
         except.handles(result) and
         result = this.innateException()
@@ -200,8 +200,8 @@ class RaisingNode extends ControlFlowNode {
     succ = this.getAnExceptionalSuccessor() and
     (
       /* An 'except' that handles raised and there is no more previous handler */
-      succ.(ExceptFlowNode).handles_objectapi(raised) and
-      not exists(ExceptFlowNode other, StmtList s, int i, int j |
+      succ.(ExceptFlowNodeWithPointsTo).handles_objectapi(raised) and
+      not exists(ExceptFlowNodeWithPointsTo other, StmtList s, int i, int j |
         not other = succ and
         other.handles_objectapi(raised) and
         s.getItem(i) = succ.getNode() and
@@ -211,7 +211,7 @@ class RaisingNode extends ControlFlowNode {
       )
       or
       /* Any successor that is not an 'except', provided that 'raised' is not handled by a different successor. */
-      not this.getAnExceptionalSuccessor().(ExceptFlowNode).handles_objectapi(raised) and
+      not this.getAnExceptionalSuccessor().(ExceptFlowNodeWithPointsTo).handles_objectapi(raised) and
       not succ instanceof ExceptFlowNode
     )
   }
@@ -223,8 +223,8 @@ class RaisingNode extends ControlFlowNode {
     succ = this.getAnExceptionalSuccessor() and
     (
       /* An 'except' that handles raised and there is no more previous handler */
-      succ.(ExceptFlowNode).handles(raised) and
-      not exists(ExceptFlowNode other, StmtList s, int i, int j |
+      succ.(ExceptFlowNodeWithPointsTo).handles(raised) and
+      not exists(ExceptFlowNodeWithPointsTo other, StmtList s, int i, int j |
         not other = succ and
         other.handles(raised) and
         s.getItem(i) = succ.getNode() and
@@ -234,7 +234,7 @@ class RaisingNode extends ControlFlowNode {
       )
       or
       /* Any successor that is not an 'except', provided that 'raised' is not handled by a different successor. */
-      not this.getAnExceptionalSuccessor().(ExceptFlowNode).handles(raised) and
+      not this.getAnExceptionalSuccessor().(ExceptFlowNodeWithPointsTo).handles(raised) and
       not succ instanceof ExceptFlowNode
     )
   }
@@ -248,7 +248,7 @@ class RaisingNode extends ControlFlowNode {
     raised.isLegalExceptionType() and
     raised = this.getARaisedType_objectapi() and
     this.isExceptionalExit(s) and
-    not this.getAnExceptionalSuccessor().(ExceptFlowNode).handles_objectapi(raised)
+    not this.getAnExceptionalSuccessor().(ExceptFlowNodeWithPointsTo).handles_objectapi(raised)
   }
 
   /**
@@ -260,7 +260,7 @@ class RaisingNode extends ControlFlowNode {
     raised.isLegalExceptionType() and
     raised = this.getARaisedType() and
     this.isExceptionalExit(s) and
-    not this.getAnExceptionalSuccessor().(ExceptFlowNode).handles(raised)
+    not this.getAnExceptionalSuccessor().(ExceptFlowNodeWithPointsTo).handles(raised)
   }
 }
 
@@ -368,36 +368,9 @@ predicate scope_raises_unknown(Scope s) {
   )
 }
 
-/** The ControlFlowNode for an 'except' statement. */
-class ExceptFlowNode extends ControlFlowNode {
-  ExceptFlowNode() { this.getNode() instanceof ExceptStmt }
-
-  /**
-   * Gets the type handled by this exception handler.
-   * `ExceptionType` in `except ExceptionType as e:`
-   */
-  ControlFlowNodeWithPointsTo getType() {
-    exists(ExceptStmt ex |
-      this.getBasicBlock().dominates(result.getBasicBlock()) and
-      ex = this.getNode() and
-      result = ex.getType().getAFlowNode()
-    )
-  }
-
-  /**
-   * Gets the name assigned to the handled exception, if any.
-   * `e` in `except ExceptionType as e:`
-   */
-  ControlFlowNode getName() {
-    exists(ExceptStmt ex |
-      this.getBasicBlock().dominates(result.getBasicBlock()) and
-      ex = this.getNode() and
-      result = ex.getName().getAFlowNode()
-    )
-  }
-
+class ExceptFlowNodeWithPointsTo extends ExceptFlowNode {
   private predicate handledObject_objectapi(Object obj, ClassObject cls, ControlFlowNode origin) {
-    this.getType().refersTo(obj, cls, origin)
+    this.getType().(ControlFlowNodeWithPointsTo).refersTo(obj, cls, origin)
     or
     exists(Object tup | this.handledObject_objectapi(tup, theTupleType(), _) |
       element_from_tuple_objectapi(tup).refersTo(obj, cls, origin)
@@ -407,7 +380,7 @@ class ExceptFlowNode extends ControlFlowNode {
   private predicate handledObject(Value val, ClassValue cls, ControlFlowNode origin) {
     val.getClass() = cls and
     (
-      this.getType().pointsTo(val, origin)
+      this.getType().(ControlFlowNodeWithPointsTo).pointsTo(val, origin)
       or
       exists(TupleValue tup | this.handledObject(tup, ClassValue::tuple(), _) |
         val = tup.getItem(_) and origin = val.getOrigin()
@@ -452,29 +425,6 @@ class ExceptFlowNode extends ControlFlowNode {
   }
 }
 
-/** The ControlFlowNode for an 'except*' statement. */
-class ExceptGroupFlowNode extends ControlFlowNode {
-  ExceptGroupFlowNode() { this.getNode() instanceof ExceptGroupStmt }
-
-  /**
-   * Gets the type handled by this exception handler.
-   * `ExceptionType` in `except* ExceptionType as e:`
-   */
-  ControlFlowNode getType() {
-    this.getBasicBlock().dominates(result.getBasicBlock()) and
-    result = this.getNode().(ExceptGroupStmt).getType().getAFlowNode()
-  }
-
-  /**
-   * Gets the name assigned to the handled exception, if any.
-   * `e` in `except* ExceptionType as e:`
-   */
-  ControlFlowNode getName() {
-    this.getBasicBlock().dominates(result.getBasicBlock()) and
-    result = this.getNode().(ExceptGroupStmt).getName().getAFlowNode()
-  }
-}
-
 private ControlFlowNodeWithPointsTo element_from_tuple_objectapi(Object tuple) {
   exists(Tuple t | t = tuple.getOrigin() and result = t.getAnElt().getAFlowNode())
 }

python/ql/src/Exceptions/IllegalExceptionHandlerType.ql

@@ -14,7 +14,7 @@
 import python
 private import LegacyPointsTo
 
-from ExceptFlowNode ex, Value t, ClassValue c, ControlFlowNode origin, string what
+from ExceptFlowNodeWithPointsTo ex, Value t, ClassValue c, ControlFlowNode origin, string what
 where
   ex.handledException(t, c, origin) and
   (

python/ql/test/2/library-tests/ControlFlow/Exceptions/Handles.ql

@@ -1,6 +1,6 @@
 import python
 private import LegacyPointsTo
 
-from ExceptFlowNode ex, Value val
+from ExceptFlowNodeWithPointsTo ex, Value val
 where ex.handledException(val, _, _)
 select ex.getLocation().getStartLine(), ex.toString(), val.toString()

python/ql/test/3/library-tests/ControlFlow/Exceptions/Handles.ql

@@ -1,6 +1,6 @@
 import python
 private import LegacyPointsTo
 
-from ExceptFlowNode ex, Value val
+from ExceptFlowNodeWithPointsTo ex, Value val
 where ex.handledException(val, _, _)
 select ex.getLocation().getStartLine(), ex.toString(), val.toString()

python/ql/test/library-tests/exceptions/Handles.ql

@@ -1,6 +1,6 @@
 import python
 private import LegacyPointsTo
 
-from ExceptFlowNode ex, Value val
+from ExceptFlowNodeWithPointsTo ex, Value val
 where ex.handledException(val, _, _)
 select ex.getLocation().getStartLine(), ex.toString(), val.toString()

python/ql/test/library-tests/types/exceptions/Handles.ql

@@ -1,6 +1,6 @@
 import python
 private import LegacyPointsTo
 
-from ExceptFlowNode n, ClassObject cls
+from ExceptFlowNodeWithPointsTo n, ClassObject cls
 where n.handles_objectapi(cls)
 select n.getLocation().getStartLine(), cls.toString()