Rust: Remove spurious CFG edges in match expressions

Author: hvitved

rust/ql/lib/codeql/rust/controlflow/internal/ControlFlowGraphImpl.qll

@@ -356,24 +356,27 @@ class MatchArmTree extends ControlFlowTree instanceof MatchArm {
 
 class MatchExprTree extends PostOrderTree instanceof MatchExpr {
   override predicate propagatesAbnormal(AstNode child) {
-    child = [super.getExpr(), super.getMatchArmList().getAnArm().getExpr()]
+    child = [super.getExpr(), super.getAnArm().getExpr()]
   }
 
   override predicate first(AstNode node) { first(super.getExpr(), node) }
 
   override predicate succ(AstNode pred, AstNode succ, Completion c) {
     // Edge from the scrutinee to the first arm.
-    last(super.getExpr(), pred, c) and succ = super.getMatchArmList().getArm(0).getPat()
+    last(super.getExpr(), pred, c) and succ = super.getArm(0).getPat()
     or
     // Edge from a failed match/guard in one arm to the beginning of the next arm.
     exists(int i |
-      last(super.getMatchArmList().getArm(i), pred, c) and
-      first(super.getMatchArmList().getArm(i + 1), succ) and
+      last(super.getArm(i), pred, c) and
+      first(super.getArm(i + 1), succ) and
       c.(ConditionalCompletion).failed()
     )
     or
     // Edge from the end of each arm to the match expression.
-    last(super.getMatchArmList().getArm(_), pred, c) and succ = this and completionIsNormal(c)
+    last(super.getArm(_).getExpr(), pred, c) and succ = this and completionIsNormal(c)
+    or
+    // Edge from the end of last arm to the match expression.
+    last(super.getLastArm().getExpr(), pred, c) and succ = this and completionIsNormal(c)
   }
 }
 

rust/ql/lib/codeql/rust/elements/internal/MatchExprImpl.qll

@@ -181,11 +181,9 @@
 | test.rs:94:12:94:46 | ParenExpr | test.rs:97:13:97:13 | LiteralExpr | false |
 | test.rs:94:13:94:45 | MatchExpr | test.rs:94:12:94:46 | ParenExpr |  |
 | test.rs:94:19:94:19 | PathExpr | test.rs:94:23:94:23 | LiteralPat |  |
-| test.rs:94:23:94:23 | LiteralPat | test.rs:94:13:94:45 | MatchExpr | no-match |
 | test.rs:94:23:94:23 | LiteralPat | test.rs:94:28:94:31 | LiteralExpr | match |
 | test.rs:94:23:94:23 | LiteralPat | test.rs:94:34:94:34 | WildcardPat | no-match |
 | test.rs:94:28:94:31 | LiteralExpr | test.rs:94:13:94:45 | MatchExpr |  |
-| test.rs:94:34:94:34 | WildcardPat | test.rs:94:13:94:45 | MatchExpr | no-match |
 | test.rs:94:34:94:34 | WildcardPat | test.rs:94:39:94:43 | LiteralExpr | match |
 | test.rs:94:39:94:43 | LiteralExpr | test.rs:94:13:94:45 | MatchExpr |  |
 | test.rs:94:48:96:9 | BlockExpr | test.rs:94:9:98:9 | IfExpr |  |
@@ -239,16 +237,13 @@
 | test.rs:122:44:128:1 | BlockExpr | test.rs:122:1:128:1 | exit test_match (normal) |  |
 | test.rs:123:5:127:5 | MatchExpr | test.rs:122:44:128:1 | BlockExpr |  |
 | test.rs:123:11:123:21 | PathExpr | test.rs:124:9:124:23 | TupleStructPat |  |
-| test.rs:124:9:124:23 | TupleStructPat | test.rs:123:5:127:5 | MatchExpr | no-match |
 | test.rs:124:9:124:23 | TupleStructPat | test.rs:124:28:124:28 | PathExpr | match |
 | test.rs:124:9:124:23 | TupleStructPat | test.rs:125:9:125:23 | TupleStructPat | no-match |
 | test.rs:124:28:124:28 | PathExpr | test.rs:124:32:124:33 | LiteralExpr |  |
 | test.rs:124:32:124:33 | LiteralExpr | test.rs:124:28:124:33 | BinaryExpr |  |
-| test.rs:125:9:125:23 | TupleStructPat | test.rs:123:5:127:5 | MatchExpr | no-match |
 | test.rs:125:9:125:23 | TupleStructPat | test.rs:125:28:125:28 | PathExpr | match |
 | test.rs:125:9:125:23 | TupleStructPat | test.rs:126:9:126:20 | PathPat | no-match |
 | test.rs:125:28:125:28 | PathExpr | test.rs:123:5:127:5 | MatchExpr |  |
-| test.rs:126:9:126:20 | PathPat | test.rs:123:5:127:5 | MatchExpr | no-match |
 | test.rs:126:9:126:20 | PathPat | test.rs:126:25:126:25 | LiteralExpr | match |
 | test.rs:126:25:126:25 | LiteralExpr | test.rs:123:5:127:5 | MatchExpr |  |
 | test.rs:131:5:136:5 | enter test_infinite_loop | test.rs:132:9:134:9 | ExprStmt |  |