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C#: Data flow for positional patterns. #22689

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6e44cf9
C#: Add some positional pattern data flow tests.
michaelnebel Sep 24, 2026
fc6eb67
C#: Make positional pattern read step.
michaelnebel Sep 28, 2026
6ecc8f3
C#: Update test expected output.
michaelnebel Sep 28, 2026
21dde8a
C#: Refactor the tuple read step logic that is only relevant to patte…
michaelnebel Sep 29, 2026
ae1c4ad
C#: Add change-note.
michaelnebel Oct 2, 2026
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4 changes: 4 additions & 0 deletions csharp/ql/lib/change-notes/2026-10-02-positional-pattern-flow.md
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@@ -0,0 +1,4 @@
---
category: minorAnalysis
---
* Added support for data flow through positional patterns in `is` expressions and `switch` cases.
53 changes: 44 additions & 9 deletions csharp/ql/lib/semmle/code/csharp/dataflow/internal/DataFlowPrivate.qll
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Expand Up @@ -563,13 +563,19 @@ module LocalFlow {
exists(IsExpr e |
e1 = e.getExpr() and
e2 = e.getPattern() and
e2 instanceof TuplePatternExpr
(
e2 instanceof TuplePatternExpr or
e2 instanceof RecursivePatternExpr
)
)
or
exists(Switch sw |
e1 = sw.getExpr() and
e2 = sw.getACase().getPattern() and
e2 instanceof TuplePatternExpr
(
e2 instanceof TuplePatternExpr or
e2 instanceof RecursivePatternExpr
)
)
}

Expand Down Expand Up @@ -2208,6 +2214,40 @@ predicate storeStep(Node node1, ContentSet c, Node node2) {
storeStepDelegateCall(node1, c, node2)
}

private predicate readStepPattern(Node node1, Content c, Node node2) {
exists(RecursivePatternExpr pattern, PatternExpr item, int i |
node1.asExpr() = pattern and
item = pattern.getPositionalPatterns().getPattern(i) and
c.(FieldContent).getField() =
pattern.getType().(TupleType).getElement(i).getUnboundDeclaration()
|
// item = { ... } in node1 = (var ..., { ... })
item = node2.asExpr().(RecursivePatternExpr)
or
// item = (...,...) in node1 = (var ..., (..., ...))
item = node2.asExpr().(TuplePatternExpr)
or
// item = variable in node1 = (..., variable, ...) in a case/is (var ..., var ...)
exists(AssignableDefinitions::PatternDefinition lvd |
node2.(AssignableDefinitionNode).getDefinition() = lvd and
item = lvd.getDeclaration()
)
)
or
// item = variable in node1 = (..., variable, ...) in a case/is var (..., ...)
exists(TuplePatternExpr pattern, PatternExpr item, int i |
node1.asExpr() = pattern and
c.(FieldContent).getField() =
pattern.getType().(TupleType).getElement(i).getUnboundDeclaration() and
item = pattern.getArgument(i)
|
exists(AssignableDefinitions::PatternDefinition lvd |
node2.(AssignableDefinitionNode).getDefinition() = lvd and
item = lvd.getDeclaration()
)
)
}

private predicate readContentStep(Node node1, Content c, Node node2) {
arrayRead(node1.asExpr(), node2.asExpr()) and
c instanceof ElementContent
Expand Down Expand Up @@ -2246,15 +2286,10 @@ private predicate readContentStep(Node node1, Content c, Node node2) {
node2.(AssignableDefinitionNode).getDefinition() = tad and
tad.getLeaf() = item
)
or
// item = variable in node1 = (..., variable, ...) in a case/is var (..., ...)
te instanceof TuplePatternExpr and
exists(AssignableDefinitions::PatternDefinition lvd |
node2.(AssignableDefinitionNode).getDefinition() = lvd and
lvd.getDeclaration() = item
)
)
or
readStepPattern(node1, c, node2)
or
VariableCapture::readStep(node1, c, node2)
}

Expand Down
41 changes: 40 additions & 1 deletion csharp/ql/test/library-tests/dataflow/tuples/DataFlowStep.expected
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Expand Up @@ -143,6 +143,7 @@
| Tuples.cs:75:13:75:30 | SSA qualifier def(y.Item2.Item2) | Tuples.cs:80:22:80:34 | access to field Item2 |
| Tuples.cs:75:17:75:30 | (..., ...) | Tuples.cs:75:13:75:13 | access to local variable y |
| Tuples.cs:75:18:75:18 | access to parameter s | Tuples.cs:75:25:75:25 | access to parameter s |
| Tuples.cs:76:17:76:17 | access to local variable y | Tuples.cs:78:18:78:39 | { ... } |
| Tuples.cs:76:17:76:17 | access to local variable y | Tuples.cs:79:22:79:22 | access to local variable y |
| Tuples.cs:78:19:78:23 | SSA def(a) | Tuples.cs:78:46:78:46 | access to local variable a |
| Tuples.cs:78:19:78:23 | String a | Tuples.cs:78:19:78:23 | SSA def(a) |
Expand Down Expand Up @@ -226,4 +227,42 @@
| Tuples.cs:133:24:133:29 | (..., ...) | Tuples.cs:133:9:133:20 | (..., ...) |
| Tuples.cs:133:25:133:25 | 1 | Tuples.cs:133:9:133:29 | ... = ... |
| Tuples.cs:133:28:133:28 | access to local variable o | Tuples.cs:133:18:133:19 | access to local variable y4 |
| Tuples.cs:144:18:144:31 | this | Tuples.cs:144:18:144:31 | this access |
| Tuples.cs:139:13:139:14 | access to local variable o1 | Tuples.cs:139:13:139:35 | SSA def(o1) |
| Tuples.cs:139:13:139:35 | SSA def(o1) | Tuples.cs:141:18:141:19 | access to local variable o1 |
| Tuples.cs:139:18:139:35 | call to method Source<String> | Tuples.cs:139:13:139:14 | access to local variable o1 |
| Tuples.cs:139:33:139:34 | 10 | Tuples.cs:139:33:139:34 | (...) ... |
| Tuples.cs:140:13:140:14 | access to local variable o2 | Tuples.cs:140:13:140:35 | SSA def(o2) |
| Tuples.cs:140:13:140:35 | SSA def(o2) | Tuples.cs:141:26:141:27 | access to local variable o2 |
| Tuples.cs:140:18:140:35 | call to method Source<String> | Tuples.cs:140:13:140:14 | access to local variable o2 |
| Tuples.cs:140:33:140:34 | 11 | Tuples.cs:140:33:140:34 | (...) ... |
| Tuples.cs:141:13:141:13 | access to local variable x | Tuples.cs:141:13:141:32 | SSA def(x) |
| Tuples.cs:141:13:141:32 | SSA def(x) | Tuples.cs:142:17:142:17 | access to local variable x |
| Tuples.cs:141:17:141:32 | (..., ...) | Tuples.cs:141:13:141:13 | access to local variable x |
| Tuples.cs:142:17:142:17 | access to local variable x | Tuples.cs:144:18:144:46 | { ... } |
| Tuples.cs:144:19:144:24 | SSA def(a1) | Tuples.cs:145:22:145:23 | access to local variable a1 |
| Tuples.cs:144:19:144:24 | String a1 | Tuples.cs:144:19:144:24 | SSA def(a1) |
| Tuples.cs:144:28:144:33 | Int32 b1 | Tuples.cs:144:28:144:33 | SSA def(b1) |
| Tuples.cs:144:28:144:33 | SSA def(b1) | Tuples.cs:147:22:147:23 | access to local variable b1 |
| Tuples.cs:144:36:144:41 | SSA def(c1) | Tuples.cs:146:22:146:23 | access to local variable c1 |
| Tuples.cs:144:36:144:41 | String c1 | Tuples.cs:144:36:144:41 | SSA def(c1) |
| Tuples.cs:147:22:147:23 | access to local variable b1 | Tuples.cs:147:22:147:23 | (...) ... |
| Tuples.cs:151:13:151:14 | access to local variable o3 | Tuples.cs:151:13:151:35 | SSA def(o3) |
| Tuples.cs:151:13:151:35 | SSA def(o3) | Tuples.cs:153:18:153:19 | access to local variable o3 |
| Tuples.cs:151:18:151:35 | call to method Source<String> | Tuples.cs:151:13:151:14 | access to local variable o3 |
| Tuples.cs:151:33:151:34 | 12 | Tuples.cs:151:33:151:34 | (...) ... |
| Tuples.cs:152:13:152:14 | access to local variable o4 | Tuples.cs:152:13:152:35 | SSA def(o4) |
| Tuples.cs:152:13:152:35 | SSA def(o4) | Tuples.cs:153:26:153:27 | access to local variable o4 |
| Tuples.cs:152:18:152:35 | call to method Source<String> | Tuples.cs:152:13:152:14 | access to local variable o4 |
| Tuples.cs:152:33:152:34 | 13 | Tuples.cs:152:33:152:34 | (...) ... |
| Tuples.cs:153:13:153:13 | access to local variable y | Tuples.cs:153:13:153:32 | SSA def(y) |
| Tuples.cs:153:13:153:32 | SSA def(y) | Tuples.cs:154:13:154:13 | access to local variable y |
| Tuples.cs:153:17:153:32 | (..., ...) | Tuples.cs:153:13:153:13 | access to local variable y |
| Tuples.cs:154:13:154:13 | access to local variable y | Tuples.cs:154:18:154:42 | { ... } |
| Tuples.cs:154:19:154:24 | SSA def(a2) | Tuples.cs:156:18:156:19 | access to local variable a2 |
| Tuples.cs:154:19:154:24 | String a2 | Tuples.cs:154:19:154:24 | SSA def(a2) |
| Tuples.cs:154:32:154:33 | Int32 b2 | Tuples.cs:154:32:154:33 | SSA def(b2) |
| Tuples.cs:154:32:154:33 | SSA def(b2) | Tuples.cs:158:18:158:19 | access to local variable b2 |
| Tuples.cs:154:36:154:37 | SSA def(c2) | Tuples.cs:157:18:157:19 | access to local variable c2 |
| Tuples.cs:154:36:154:37 | String c2 | Tuples.cs:154:36:154:37 | SSA def(c2) |
| Tuples.cs:158:18:158:19 | access to local variable b2 | Tuples.cs:158:18:158:19 | (...) ... |
| Tuples.cs:169:18:169:31 | this | Tuples.cs:169:18:169:31 | this access |
120 changes: 107 additions & 13 deletions csharp/ql/test/library-tests/dataflow/tuples/PrintAst.expected
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Expand Up @@ -504,20 +504,114 @@ Tuples.cs:
# 134| 12: [ExprStmt] ...;
# 134| 0: [MethodCall] call to method Sink
# 134| 0: [LocalVariableAccess] access to local variable y4
# 137| 13: [Method] Sink
# 137| 13: [Method] M7
# 137| -1: [TypeMention] Void
# 138| 4: [BlockStmt] {...}
# 139| 0: [LocalVariableDeclStmt] ... ...;
# 139| 0: [LocalVariableDeclAndInitExpr] String o1 = ...
# 139| -1: [TypeMention] string
# 139| 0: [LocalVariableAccess] access to local variable o1
# 139| 1: [MethodCall] call to method Source<String>
# 139| 0: [CastExpr] (...) ...
# 139| 1: [IntLiteral] 10
# 140| 1: [LocalVariableDeclStmt] ... ...;
# 140| 0: [LocalVariableDeclAndInitExpr] String o2 = ...
# 140| -1: [TypeMention] string
# 140| 0: [LocalVariableAccess] access to local variable o2
# 140| 1: [MethodCall] call to method Source<String>
# 140| 0: [CastExpr] (...) ...
# 140| 1: [IntLiteral] 11
# 141| 2: [LocalVariableDeclStmt] ... ...;
# 141| 0: [LocalVariableDeclAndInitExpr] (String,(Int32,String),Int32) x = ...
# 141| -1: [TypeMention] (string, (int, string), int)
# 141| 0: [LocalVariableAccess] access to local variable x
# 141| 1: [TupleExpr] (..., ...)
# 141| 0: [LocalVariableAccess] access to local variable o1
# 141| 1: [TupleExpr] (..., ...)
# 141| 0: [IntLiteral] 2
# 141| 1: [LocalVariableAccess] access to local variable o2
# 141| 2: [IntLiteral] 3
# 142| 3: [SwitchStmt] switch (...) {...}
# 142| 0: [LocalVariableAccess] access to local variable x
# 144| 0: [CaseStmt] case ...:
# 144| 0: [RecursivePatternExpr] { ... }
# 144| 2: [PositionalPatternExpr] ( ... )
# 144| 0: [VariablePatternExpr] String a1
# 144| 1: [RecursivePatternExpr] { ... }
# 144| 2: [PositionalPatternExpr] ( ... )
# 144| 0: [VariablePatternExpr] Int32 b1
# 144| 1: [VariablePatternExpr] String c1
# 144| 2: [DiscardPatternExpr] _
# 145| 1: [ExprStmt] ...;
# 145| 0: [MethodCall] call to method Sink
# 145| 0: [LocalVariableAccess] access to local variable a1
# 146| 2: [ExprStmt] ...;
# 146| 0: [MethodCall] call to method Sink
# 146| 0: [LocalVariableAccess] access to local variable c1
# 147| 3: [ExprStmt] ...;
# 147| 0: [MethodCall] call to method Sink
# 147| 0: [CastExpr] (...) ...
# 147| 1: [LocalVariableAccess] access to local variable b1
# 148| 4: [BreakStmt] break;
# 151| 4: [LocalVariableDeclStmt] ... ...;
# 151| 0: [LocalVariableDeclAndInitExpr] String o3 = ...
# 151| -1: [TypeMention] string
# 151| 0: [LocalVariableAccess] access to local variable o3
# 151| 1: [MethodCall] call to method Source<String>
# 151| 0: [CastExpr] (...) ...
# 151| 1: [IntLiteral] 12
# 152| 5: [LocalVariableDeclStmt] ... ...;
# 152| 0: [LocalVariableDeclAndInitExpr] String o4 = ...
# 152| -1: [TypeMention] string
# 152| 0: [LocalVariableAccess] access to local variable o4
# 152| 1: [MethodCall] call to method Source<String>
# 152| 0: [CastExpr] (...) ...
# 152| 1: [IntLiteral] 13
# 153| 6: [LocalVariableDeclStmt] ... ...;
# 153| 0: [LocalVariableDeclAndInitExpr] (String,(Int32,String),Int32) y = ...
# 153| -1: [TypeMention] (string, (int, string), int)
# 153| 0: [LocalVariableAccess] access to local variable y
# 153| 1: [TupleExpr] (..., ...)
# 153| 0: [LocalVariableAccess] access to local variable o3
# 153| 1: [TupleExpr] (..., ...)
# 153| 0: [IntLiteral] 2
# 153| 1: [LocalVariableAccess] access to local variable o4
# 153| 2: [IntLiteral] 3
# 154| 7: [IfStmt] if (...) ...
# 154| 0: [IsExpr] ... is ...
# 154| 0: [LocalVariableAccess] access to local variable y
# 154| 1: [RecursivePatternExpr] { ... }
# 154| 2: [PositionalPatternExpr] ( ... )
# 154| 0: [VariablePatternExpr] String a2
# 154| 1: [TuplePatternExpr] (..., ...)
# 154| 0: [VariablePatternExpr] Int32 b2
# 154| 1: [VariablePatternExpr] String c2
# 154| 2: [DiscardPatternExpr] _
# 155| 1: [BlockStmt] {...}
# 156| 0: [ExprStmt] ...;
# 156| 0: [MethodCall] call to method Sink
# 156| 0: [LocalVariableAccess] access to local variable a2
# 157| 1: [ExprStmt] ...;
# 157| 0: [MethodCall] call to method Sink
# 157| 0: [LocalVariableAccess] access to local variable c2
# 158| 2: [ExprStmt] ...;
# 158| 0: [MethodCall] call to method Sink
# 158| 0: [CastExpr] (...) ...
# 158| 1: [LocalVariableAccess] access to local variable b2
# 162| 14: [Method] Sink
# 162| -1: [TypeMention] Void
#-----| 2: (Parameters)
# 137| 0: [Parameter] o
# 137| -1: [TypeMention] object
# 137| 4: [BlockStmt] {...}
# 139| 16: [Method] Source`1
# 139| -1: [TypeMention] T
# 162| 0: [Parameter] o
# 162| -1: [TypeMention] object
# 162| 4: [BlockStmt] {...}
# 164| 17: [Method] Source`1
# 164| -1: [TypeMention] T
#-----| 1: (Type parameters)
# 139| 0: [TypeParameter] T
# 164| 0: [TypeParameter] T
#-----| 2: (Parameters)
# 139| 0: [Parameter] source
# 139| -1: [TypeMention] object
# 139| 4: [ThrowExpr] throw ...
# 139| 0: [NullLiteral] null
# 142| [NamespaceDeclaration] namespace ... { ... }
# 144| 1: [Class] IsExternalInit
# 164| 0: [Parameter] source
# 164| -1: [TypeMention] object
# 164| 4: [ThrowExpr] throw ...
# 164| 0: [NullLiteral] null
# 167| [NamespaceDeclaration] namespace ... { ... }
# 169| 1: [Class] IsExternalInit
25 changes: 25 additions & 0 deletions csharp/ql/test/library-tests/dataflow/tuples/Tuples.cs
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Expand Up @@ -134,6 +134,31 @@ static void M6()
Sink(y4); // $ hasValueFlow=9
}

static void M7()
{
var o1 = Source<string>(10);
var o2 = Source<string>(11);
var x = (o1, (2, o2), 3);
switch (x)
{
case (var a1, (var b1, var c1), _):
Sink(a1); // $ hasValueFlow=10
Sink(c1); // $ hasValueFlow=11
Sink(b1);
break;
}

var o3 = Source<string>(12);
var o4 = Source<string>(13);
var y = (o3, (2, o4), 3);
if (y is (var a2, var (b2, c2), _))
{
Sink(a2); // $ hasValueFlow=12
Sink(c2); // $ hasValueFlow=13
Sink(b2);
}
}

public static void Sink(object o) { }

static T Source<T>(object source) => throw null;
Expand Down
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