Unified: Treat Unified Swift switches as exhaustive

Use the shared exhaustive-switch handling.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Copilot-Session: 4a9b52f8-d07b-4692-8fb9-409f0efd64f2

Author: paldepind

unified/ql/lib/codeql/unified/internal/ControlFlowGraph.qll

@@ -325,6 +325,9 @@ private module Input implements InputSig1, InputSig2 {
 
   class CallableContext = Void;
 
+  // Swift switches are exhaustive.
+  predicate isExhaustive(Ast::Switch switch) { any() }
+
   predicate beginAbruptCompletion(
     AstNode ast, PreControlFlowNode n, AbruptCompletion c, boolean always
   ) {

unified/ql/test/library-tests/controlflow/basicblock-slices.expected

@@ -501,7 +501,6 @@
 | 618 | cfg.swift:618:7:618:14 | Block | 'Block -V 1 -^ ReturnExpr' |
 | 619 | cfg.swift:619:5:620:14 | SwitchCase | 'SwitchCase -V false' |
 | 620 | cfg.swift:620:7:620:14 | Block | 'Block -V 0 -^ ReturnExpr' |
-| 622 | cfg.swift:622:11:622:11 | 1 | '1 -^ - ... -^ ReturnExpr' |
 | 625 | cfg.swift:625:1:635:1 | func exhaustiveEnumSwitch | 'func exhaustiveEnumSwitch -V exhaustiveEnumSwitch' |
 | 625 | cfg.swift:625:29:625:33 | value | 'value -> flag -> Block' |
 | 626 | cfg.swift:626:3:633:3 | SwitchExpr | 'SwitchExpr -V value' |
@@ -511,4 +510,3 @@
 | 630 | cfg.swift:630:7:630:14 | Block | 'Block -V 2 -^ ReturnExpr' |
 | 631 | cfg.swift:631:5:632:14 | SwitchCase | 'SwitchCase -V . -^ ... .error2 -> . -^ ... .error3 -^ OrPattern' |
 | 632 | cfg.swift:632:7:632:14 | Block | 'Block -V 3 -^ ReturnExpr' |
-| 634 | cfg.swift:634:11:634:11 | 1 | '1 -^ - ... -^ ReturnExpr' |

unified/ql/test/library-tests/controlflow/cfg.expected

@@ -152,14 +152,10 @@ bbStep
 | cfg.swift:600:13:600:18 | ... < ... | '... < ... : true -> Block(+0)' |
 | cfg.swift:617:10:617:13 | true | 'true : match -> Block(+1)' |
 | cfg.swift:617:10:617:13 | true | 'true : no-match -> SwitchCase(+2)' |
-| cfg.swift:619:10:619:14 | false | 'false : match -> Block(+1)' |
-| cfg.swift:619:10:619:14 | false | 'false : no-match -> 1(+3)' |
 | cfg.swift:627:10:627:27 | ConditionalPattern | 'ConditionalPattern : match -> Block(+1)' |
 | cfg.swift:627:10:627:27 | ConditionalPattern | 'ConditionalPattern : no-match -> SwitchCase(+2)' |
 | cfg.swift:629:10:629:16 | ... .error1 | '... .error1 : match -> Block(+1)' |
 | cfg.swift:629:10:629:16 | ... .error1 | '... .error1 : no-match -> SwitchCase(+2)' |
-| cfg.swift:631:10:631:25 | OrPattern | 'OrPattern : match -> Block(+1)' |
-| cfg.swift:631:10:631:25 | OrPattern | 'OrPattern : no-match -> 1(+3)' |
 noCfg
 | cfg.swift:47:42:47:47 | String |
 | cfg.swift:53:34:53:34 | _ |
@@ -179,6 +175,8 @@ noCfg
 | cfg.swift:440:5:440:8 | init |
 | cfg.swift:506:25:506:27 | Int |
 | cfg.swift:564:49:564:51 | Int |
+| cfg.swift:622:3:622:11 | ReturnExpr |
+| cfg.swift:634:3:634:11 | ReturnExpr |
 nonSimple
 | cfg.swift:12:17:12:25 | withParam | 'withParam -? Block' |
 | cfg.swift:35:5:35:5 | CatchClause | 'CatchClause -V MyError -^ ... .error1 -> isZero -> Argument -V x -^ isZero(...) -? MyError -^ ... .error2 -^ ConditionalPattern -^ OrPattern' |

unified/ql/test/library-tests/controlflow/cfg.swift

@@ -616,10 +616,10 @@ func exhaustiveBoolSwitch(_ value: Bool) -> Int {
   switch value {
     case true: // $ bbStep='true : match -> Block(+1)' bbStep='true : no-match -> SwitchCase(+2)'
       return 1
-    case false: // $ bbStep='false : match -> Block(+1)' bbStep='false : no-match -> 1(+3)'
+    case false:
       return 0
   }
-  return -1
+  return -1 // $ noCfg
 }
 
 func exhaustiveEnumSwitch(_ value: MyError, _ flag: Bool) -> Int {
@@ -628,8 +628,8 @@ func exhaustiveEnumSwitch(_ value: MyError, _ flag: Bool) -> Int {
       return 1
     case .error1: // $ bbStep='... .error1 : match -> Block(+1)' bbStep='... .error1 : no-match -> SwitchCase(+2)'
       return 2
-    case .error2, .error3: // $ bbStep='OrPattern : match -> Block(+1)' bbStep='OrPattern : no-match -> 1(+3)'
+    case .error2, .error3:
       return 3
   }
-  return -1
+  return -1 // $ noCfg
 }