Rust: Label the non-return CFG edge out of question mark as match

Author: paldepind

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

@@ -36,13 +36,7 @@ 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)
-    or
-    // A `?` expression can both proceed normally or cause an early return, so
-    // we explicitly allow the former here.
-    e instanceof TryExpr
-  }
+  override predicate isValidFor(AstNode e) { not any(Completion c).isValidForSpecific(e) }
 
   override string toString() { result = "simple" }
 }
@@ -177,6 +171,8 @@ class MatchCompletion extends TMatchCompletion, ConditionalCompletion {
   override predicate isValidForSpecific(AstNode e) {
     e instanceof Pat and
     if isExhaustiveMatch(e) then value = true else any()
+    or
+    e instanceof TryExpr and value = true
   }
 
   override MatchSuccessor getAMatchingSuccessorType() { result.getValue() = value }

rust/ql/test/library-tests/controlflow/Cfg.expected

@@ -575,7 +575,7 @@ edges
 | test.rs:263:9:263:11 | PathExpr | test.rs:263:9:263:26 | MethodCallExpr |  |
 | test.rs:263:9:263:26 | MethodCallExpr | test.rs:263:9:263:27 | TryExpr |  |
 | test.rs:263:9:263:27 | TryExpr | test.rs:262:5:264:5 | exit test_question_mark_operator_1 (normal) | return |
-| test.rs:263:9:263:27 | TryExpr | test.rs:263:31:263:31 | 4 |  |
+| test.rs:263:9:263:27 | TryExpr | test.rs:263:31:263:31 | 4 | match |
 | test.rs:263:9:263:31 | ... + ... | test.rs:262:62:264:5 | BlockExpr |  |
 | test.rs:263:31:263:31 | 4 | test.rs:263:9:263:31 | ... + ... |  |
 | test.rs:266:5:271:5 | enter test_question_mark_operator_2 | test.rs:266:38:266:38 | b |  |
@@ -586,7 +586,7 @@ edges
 | test.rs:267:9:270:9 | MatchExpr | test.rs:266:71:271:5 | BlockExpr |  |
 | test.rs:267:15:267:15 | b | test.rs:267:15:267:16 | TryExpr |  |
 | test.rs:267:15:267:16 | TryExpr | test.rs:266:5:271:5 | exit test_question_mark_operator_2 (normal) | return |
-| test.rs:267:15:267:16 | TryExpr | test.rs:268:13:268:16 | LiteralPat |  |
+| test.rs:267:15:267:16 | TryExpr | test.rs:268:13:268:16 | LiteralPat | match |
 | test.rs:268:13:268:16 | LiteralPat | test.rs:268:21:268:24 | PathExpr | match |
 | test.rs:268:13:268:16 | LiteralPat | test.rs:269:13:269:17 | LiteralPat | no-match |
 | test.rs:268:21:268:24 | PathExpr | test.rs:268:26:268:30 | false |  |