pythos: SSA for match

- new SSA definition `PatternCaptureDefinition`
- new SSA definition `PatternAliasDefinition`
- implement `hasDefiningNode`

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

@@ -70,6 +70,10 @@ abstract class SsaSourceVariable extends @py_variable {
     SsaSource::exception_capture(this, def)
     or
     SsaSource::with_definition(this, def)
+    or
+    SsaSource::pattern_capture_definition(this, def)
+    or
+    SsaSource::pattern_alias_definition(this, def)
   }
 
   /**

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

@@ -545,6 +545,24 @@ class WithDefinition extends EssaNodeDefinition {
   override string getRepresentation() { result = "with" }
 }
 
+/** A definition of a variable via a capture pattern */
+class PatternCaptureDefinition extends EssaNodeDefinition {
+  PatternCaptureDefinition() {
+    SsaSource::pattern_capture_definition(this.getSourceVariable(), this.getDefiningNode())
+  }
+
+  override string getRepresentation() { result = "pattern capture" }
+}
+
+/** A definition of a variable via a pattern alias */
+class PatternAliasDefinition extends EssaNodeDefinition {
+  PatternAliasDefinition() {
+    SsaSource::pattern_alias_definition(this.getSourceVariable(), this.getDefiningNode())
+  }
+
+  override string getRepresentation() { result = "pattern alias" }
+}
+
 /** A definition of a variable by declaring it as a parameter */
 class ParameterDefinition extends EssaNodeDefinition {
   ParameterDefinition() {

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

@@ -40,6 +40,28 @@ module SsaSource {
     )
   }
 
+  /** Holds if `v` is defined by a capture pattern. */
+  cached
+  predicate pattern_capture_definition(Variable v, ControlFlowNode defn) {
+    exists(MatchCapturePattern capture, Name var |
+      capture.getVariable() = var and
+      var.getAFlowNode() = defn
+    |
+      var = v.getAStore()
+    )
+  }
+
+  /** Holds if `v` is defined by as the alias of an as-pattern. */
+  cached
+  predicate pattern_alias_definition(Variable v, ControlFlowNode defn) {
+    exists(MatchAsPattern pattern, Name var |
+      pattern.getAlias() = var and
+      var.getAFlowNode() = defn
+    |
+      var = v.getAStore()
+    )
+  }
+
   /** Holds if `v` is defined by multiple assignment at `defn`. */
   cached
   predicate multi_assignment_definition(Variable v, ControlFlowNode defn, int n, SequenceNode lhs) {