[rust2cpg] lower match guards. (#6223)

Author: xavierpinho

joern-cli/frontends/rust2cpg/src/main/scala/io/joern/rust2cpg/astcreation/RustVisitor.scala

@@ -1775,15 +1775,24 @@ trait RustVisitor(implicit withSchemaValidation: ValidationMode) { this: AstCrea
     Ast(blockNode(matchExpr)).withChildren(Seq(tmpLocalAst, tmpAssignAst, matchExprAst))
   }
 
-  // TODO: handle guards.
   private def lowerMatchArm(matchArm: MatchArm, tmpIdentAst: () => Ast): Seq[Ast] = {
     val bindingAsts = createLocalsForBindings(collectPatternBindings(matchArm.pat)) ++ createAssignmentsForPattern(
       matchArm.pat,
       tmpIdentAst
     )
-    val bodyAst       = visitExpr(matchArm.expr)
+    val bodyAst = matchArm.matchGuard match {
+      case Some(matchGuard) =>
+        val conditionAst = visitExpr(matchGuard.expr)
+        ifThenElseAst(matchGuard, Some(conditionAst), visitExpr(matchArm.expr), None)
+      case None =>
+        visitExpr(matchArm.expr)
+    }
+    val caseCode = matchArm.matchGuard match {
+      case Some(matchGuard) => s"${code(matchArm.pat)} ${code(matchGuard)}"
+      case None             => code(matchArm.pat)
+    }
     val matchArmBlock = blockAst(blockNode(matchArm), (bindingAsts :+ bodyAst).toList)
-    val jumpTargetAst = Ast(jumpTargetNode(matchArm.pat, s"case ${code(matchArm.pat)}", code(matchArm.pat)))
+    val jumpTargetAst = Ast(jumpTargetNode(matchArm.pat, s"case $caseCode", caseCode))
     Seq(jumpTargetAst, matchArmBlock)
   }
 

joern-cli/frontends/rust2cpg/src/test/scala/io/joern/rust2cpg/passes/ast/MatchTests.scala

@@ -112,6 +112,49 @@ class MatchTests extends Rust2CpgSuite(noSysRoot = true) {
     }
   }
 
+  "match with guards" should {
+    val cpg = code("""
+        |fn foo(x: (i32, i32)) {
+        |  match x {
+        |  (n, _) if n > 3 => bar(n),
+        |  _ if baz() => qux(),
+        |  _ => 0,
+        |  };
+        |}
+        |""".stripMargin)
+
+    "have correct jump target names" in {
+      cpg.jumpTarget.sortBy(_.order).name.l shouldBe List("case (n, _) if n > 3", "case _ if baz()", "case _")
+    }
+
+    "have correct locals" in {
+      inside(cpg.local.sortBy(_.order).l) { case tmp :: nLocal :: Nil =>
+        tmp.name shouldBe "<tmp>0"
+        tmp.typeFullName shouldBe "(i32, i32)"
+        nLocal.name shouldBe "n"
+        nLocal.typeFullName shouldBe "i32"
+      }
+    }
+
+    "have correct local assignments" in {
+      cpg.method.nameExact("foo").block.assignment.sortBy(_.order).code.l shouldBe List("<tmp>0 = x", "n = <tmp>0.0")
+    }
+
+    "have correct if control structures" in {
+      inside(cpg.ifBlock.sortBy(_.lineNumber).l) { case guard1 :: guard2 :: Nil =>
+        guard1.code shouldBe "if n > 3"
+        guard1.condition.code.l shouldBe List("n > 3")
+        guard1.whenTrue.code.l shouldBe List("bar(n)")
+        guard1.whenFalse shouldBe empty
+
+        guard2.code shouldBe "if baz()"
+        guard2.condition.code.l shouldBe List("baz()")
+        guard2.whenTrue.code.l shouldBe List("qux()")
+        guard2.whenFalse shouldBe empty
+      }
+    }
+  }
+
   "match with an or-pattern case" should {
     val cpg = code("""
         |struct Point { x: i32, y: i32 }