Merge pull request #17749 from paldepind/rust-cfg-handle-question-mark

Rust: Handle question mark operator in CFG

Author: paldepind

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

@@ -36,7 +36,13 @@ class SimpleCompletion extends NormalCompletion, TSimpleCompletion {
 
   // `SimpleCompletion` is the "default" completion type, thus it is valid for
   // any node where there isn't another more specific completion type.
-  override predicate isValidFor(AstNode e) { not any(Completion c).isValidForSpecific(e) }
+  override predicate isValidFor(AstNode e) {
+    not any(Completion c).isValidForSpecific(e)
+    or
+    // A `?` expression can both proceed normally or cause an early return, so
+    // we explicitly allow the former here.
+    e instanceof TryExpr
+  }
 
   override string toString() { result = "simple" }
 }
@@ -204,7 +210,9 @@ class ContinueCompletion extends TContinueCompletion, Completion {
 class ReturnCompletion extends TReturnCompletion, Completion {
   override ReturnSuccessor getAMatchingSuccessorType() { any() }
 
-  override predicate isValidForSpecific(AstNode e) { e instanceof ReturnExpr }
+  override predicate isValidForSpecific(AstNode e) {
+    e instanceof ReturnExpr or e instanceof TryExpr
+  }
 
   override string toString() { result = "return" }
 }

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

@@ -504,7 +504,8 @@ class MatchExprTree extends PostOrderTree instanceof MatchExpr {
   override predicate succ(AstNode pred, AstNode succ, Completion c) {
     // Edge from the scrutinee to the first arm.
     last(super.getExpr(), pred, c) and
-    first(super.getArm(0).getPat(), succ)
+    first(super.getArm(0).getPat(), succ) and
+    completionIsNormal(c)
     or
     // Edge from a failed match/guard in one arm to the beginning of the next arm.
     exists(int i |
@@ -571,18 +572,12 @@ class RefExprTree extends StandardPostOrderTree instanceof RefExpr {
   override AstNode getChildNode(int i) { i = 0 and result = super.getExpr() }
 }
 
-class ReturnExprTree extends PostOrderTree instanceof ReturnExpr {
-  override predicate propagatesAbnormal(AstNode child) { child = super.getExpr() }
-
-  override predicate first(AstNode node) {
-    first(super.getExpr(), node)
-    or
-    not super.hasExpr() and node = this
-  }
+class ReturnExprTree extends StandardPostOrderTree instanceof ReturnExpr {
+  override AstNode getChildNode(int i) { i = 0 and result = super.getExpr() }
+}
 
-  override predicate succ(AstNode pred, AstNode succ, Completion c) {
-    last(super.getExpr(), pred, c) and succ = this and completionIsNormal(c)
-  }
+class TryExprTree extends StandardPostOrderTree instanceof TryExpr {
+  override AstNode getChildNode(int i) { i = 0 and result = super.getExpr() }
 }
 
 class TupleExprTree extends StandardPostOrderTree instanceof TupleExpr {