github · aschackmull · Sep 16, 2026
@@ -7,6 +7,7 @@ module;
 private import unified
 private import codeql.controlflow.ControlFlowGraph
 private import codeql.controlflow.SuccessorType
+private import ControlFlowGraphPlugin
 
 private module Cfg0 = Make0<Location, Ast>;
 
@@ -221,6 +222,8 @@ private module Ast implements AstSig<Location> {
   }
 }
 
+private predicate mayThrow(AstNode ast) { any(ControlFlowGraphPlugin p).mayThrow(ast) }
+
 private module Input implements InputSig1, InputSig2 {
   private import codeql.util.Void
 
@@ -256,7 +259,10 @@ private module Input implements InputSig1, InputSig2 {
   predicate beginAbruptCompletion(
     AstNode ast, PreControlFlowNode n, AbruptCompletion c, boolean always
   ) {
-    none()
+    mayThrow(ast) and
+    n.isIn(ast) and
+    c.asSimpleAbruptCompletion() instanceof ExceptionSuccessor and
+    always = false
   }
 
   predicate endAbruptCompletion(AstNode ast, PreControlFlowNode n, AbruptCompletion c) { none() }

@@ -0,0 +1,10 @@
+private import unified
+private import codeql.util.Unit
+
+private module Plugins {
+  private import ControlFlowGraphPluginSwift
+}
+
+class ControlFlowGraphPlugin extends Unit {
+  predicate mayThrow(AstNode ast) { none() }
+}
@@ -0,0 +1,16 @@
+private import unified
+private import ControlFlowGraphPlugin
+
+private predicate inTry(AstNode ast) {
+  ast.(UnaryExpr).getOperator().(Token).getValue() = "try"
+  or
+  exists(AstNode parent |
+    parent = ast.getParent() and
+    inTry(ast.getParent()) and
+    not parent instanceof Callable
+  )
+}
+
+private class ControlFlowGraphPluginSwift extends ControlFlowGraphPlugin {
+  override predicate mayThrow(AstNode ast) { ast instanceof CallExpr and inTry(ast) }
+}
@@ -19,10 +19,22 @@
 | 28 | cfg.swift:28:1:45:1 | FunctionDeclaration | 'FunctionDeclaration' |
 | 28 | cfg.swift:28:15:28:15 | x | 'x -^ Block' |
 | 29 | cfg.swift:29:3:43:3 | TryExpr | 'TryExpr -V Block' |
-| 30 | cfg.swift:30:9:30:18 | mightThrow | 'mightThrow -> Argument -V 0 -^ CallExpr -^ try -^ UnaryExpr' |
+| 30 | cfg.swift:30:5:30:24 | try | 'try -^ UnaryExpr' |
+| 30 | cfg.swift:30:9:30:18 | mightThrow | 'mightThrow -> Argument -V 0 -^ CallExpr' |
 | 31 | cfg.swift:31:5:31:9 | print | 'print -> Argument -V "Did not throw." -^ CallExpr' |
 | 32 | cfg.swift:32:10:32:19 | mightThrow | 'mightThrow -> Argument -V 0 -^ CallExpr -^ try! -^ UnaryExpr' |
 | 33 | cfg.swift:33:5:33:9 | print | 'print -> Argument -V "Still did not throw." -^ CallExpr' |
+| 35 | cfg.swift:35:5:37:3 | CatchClause | 'CatchClause -V MyError -^ MemberAccessExpr -> isZero -> Argument -V x -^ CallExpr -? MyError -^ MemberAccessExpr -^ ConditionalPattern -^ OrPattern' |
+| 35 | cfg.swift:35:62:37:3 | Block | 'Block' |
+| 36 | cfg.swift:36:12:36:12 | 0 | '0 -^ ReturnExpr' |
+| 37 | cfg.swift:37:5:39:3 | CatchClause | 'CatchClause -V MyError -^ MemberAccessExpr -> Argument -V withParam -^ ExprPattern -^ CallExpr' |
+| 37 | cfg.swift:37:41:39:3 | Block | 'Block' |
+| 38 | cfg.swift:38:12:38:20 | withParam | 'withParam -^ ReturnExpr' |
+| 39 | cfg.swift:39:5:41:3 | CatchClause | 'CatchClause -V ' |
+| 39 | cfg.swift:39:22:41:3 | Block | 'Block' |
+| 40 | cfg.swift:40:5:40:9 | print | 'print -> Argument -V "MyError" -^ CallExpr' |
+| 41 | cfg.swift:41:5:43:3 | CatchClause | 'CatchClause -V Block' |
+| 42 | cfg.swift:42:5:42:9 | print | 'print -> Argument -V Unknown error  -> interpolation -V Argument -V error -^ CallExpr ->  -^ StringInterpolationExpr -^ CallExpr' |
 | 44 | cfg.swift:44:10:44:10 | 0 | '0 -^ ReturnExpr' |
 | 47 | cfg.swift:47:1:51:1 | FunctionDeclaration | 'FunctionDeclaration' |
 | 47 | cfg.swift:47:21:47:21 | s | 's -^ Block' |
@@ -311,7 +323,8 @@
 | 396 | cfg.swift:396:1:404:1 | FunctionDeclaration | 'FunctionDeclaration' |
 | 396 | cfg.swift:396:21:396:21 | x | 'x -^ Block' |
 | 397 | cfg.swift:397:3:402:3 | TryExpr | 'TryExpr -V Block' |
-| 398 | cfg.swift:398:9:398:18 | mightThrow | 'mightThrow -> Argument -V 0 -^ CallExpr -^ try -^ UnaryExpr' |
+| 398 | cfg.swift:398:5:398:24 | try | 'try -^ UnaryExpr' |
+| 398 | cfg.swift:398:9:398:18 | mightThrow | 'mightThrow -> Argument -V 0 -^ CallExpr' |
 | 399 | cfg.swift:399:5:399:9 | print | 'print -> Argument -V "Did not throw." -^ CallExpr' |
 | 400 | cfg.swift:400:10:400:19 | mightThrow | 'mightThrow -> Argument -V 0 -^ CallExpr -^ try! -^ UnaryExpr' |
 | 401 | cfg.swift:401:5:401:9 | print | 'print -> Argument -V "Still did not throw." -^ CallExpr' |

@@ -4,6 +4,17 @@ bbContinues
 | cfg.swift:525:78:525:78 | Block | 'Block goto Task(+2)' |
 | cfg.swift:526:9:526:20 | continuation | 'continuation goto Block(-1)' |
 bbStep
+| cfg.swift:30:9:30:24 | CallExpr | 'CallExpr : exception -> CatchClause(+5)' |
+| cfg.swift:30:9:30:24 | CallExpr | 'CallExpr : successor -> try(+0)' |
+| cfg.swift:33:5:33:33 | CallExpr | 'CallExpr : successor -> 0(+11)' |
+| cfg.swift:35:5:35:5 | OrPattern | 'OrPattern : match -> Block(+0)' |
+| cfg.swift:35:5:35:5 | OrPattern | 'OrPattern : no-match -> CatchClause(+2)' |
+| cfg.swift:37:11:37:39 | CallExpr | 'CallExpr : match -> Block(+0)' |
+| cfg.swift:37:11:37:39 | CallExpr | 'CallExpr : no-match -> CatchClause(+2)' |
+| cfg.swift:39:11:39:20 |  | ' : match -> Block(+0)' |
+| cfg.swift:39:11:39:20 |  | ' : no-match -> CatchClause(+2)' |
+| cfg.swift:40:5:40:20 | CallExpr | 'CallExpr : successor -> 0(+4)' |
+| cfg.swift:42:5:42:35 | CallExpr | 'CallExpr : successor -> 0(+2)' |
 | cfg.swift:140:12:140:17 | BinaryExpr | 'BinaryExpr : empty -> SwitchExpr(+3)' |
 | cfg.swift:140:12:140:17 | BinaryExpr | 'BinaryExpr : non-empty -> _(+0)' |
 | cfg.swift:141:9:141:12 | Block | 'Block : successor -> SwitchExpr(+2)' |
@@ -80,6 +91,7 @@ bbStep
 | cfg.swift:360:3:360:3 | WhileStmt | 'WhileStmt : successor -> x(+0)' |
 | cfg.swift:360:9:360:14 | BinaryExpr | 'BinaryExpr : true -> Block(+0)' |
 | cfg.swift:361:5:361:10 | CompoundAssignExpr | 'CompoundAssignExpr : successor -> x(-1)' |
+| cfg.swift:398:9:398:24 | CallExpr | 'CallExpr : successor -> try(+0)' |
 | cfg.swift:500:6:500:28 |  | ' : false -> IfExpr(+4)' |
 | cfg.swift:500:6:500:28 |  | ' : true -> Block(+0)' |
 | cfg.swift:501:5:501:10 | CompoundAssignExpr | 'CompoundAssignExpr : successor -> IfExpr(+3)' |
@@ -116,13 +128,6 @@ bbStep
 noCfg
 | cfg.swift:23:9:23:9 | x |
 | cfg.swift:24:5:24:42 | ThrowExpr |
-| cfg.swift:35:11:35:17 | MyError |
-| cfg.swift:36:5:36:12 | ReturnExpr |
-| cfg.swift:37:11:37:17 | MyError |
-| cfg.swift:38:5:38:20 | ReturnExpr |
-| cfg.swift:39:11:39:20 |  |
-| cfg.swift:40:5:40:9 | print |
-| cfg.swift:42:5:42:9 | print |
 | cfg.swift:47:42:47:47 | String |
 | cfg.swift:53:34:53:34 | _ |
 | cfg.swift:60:34:60:34 | _ |
@@ -152,6 +157,7 @@ noCfg
 | cfg.swift:559:6:559:20 | autoclosureTest |
 nonSimple
 | cfg.swift:10:1:10:1 | ClassLikeDeclaration | 'ClassLikeDeclaration -V MyError -^ BaseType -V Error' |
+| cfg.swift:35:5:35:5 | CatchClause | 'CatchClause -V MyError -^ MemberAccessExpr -> isZero -> Argument -V x -^ CallExpr -? MyError -^ MemberAccessExpr -^ ConditionalPattern -^ OrPattern' |
 | cfg.swift:209:5:209:5 | x | 'x -> x -? - -^ UnaryExpr -^ AssignExpr' |
 | cfg.swift:390:1:390:1 | ClassLikeDeclaration | 'ClassLikeDeclaration -V Derived -^ BaseType -V C' |
 | cfg.swift:527:13:527:16 | Task | 'Task -^ MemberAccessExpr -^ Argument -V FunctionExpr -^ CallExpr' |

@@ -27,19 +27,19 @@ func mightThrow(x : Int) throws -> Void {
 
 func tryCatch(x : Int) -> Int {
   do {
-    try mightThrow(x: 0)
+    try mightThrow(x: 0) // $ bbStep='CallExpr : exception -> CatchClause(+5)' bbStep='CallExpr : successor -> try(+0)'
     print("Did not throw.")
     try! mightThrow(x: 0)
-    print("Still did not throw.")
+    print("Still did not throw.") // $ bbStep='CallExpr : successor -> 0(+11)'
 
-  } catch MyError.error1 , MyError.error2 where isZero(x: x) { // $ noCfg
-    return 0 // $ noCfg
-  } catch MyError.error3(let withParam) { // $ noCfg
-    return withParam // $ noCfg
-  } catch is MyError { // $ noCfg
-    print("MyError") // $ noCfg
+  } catch MyError.error1 , MyError.error2 where isZero(x: x) { // $ bbStep='OrPattern : match -> Block(+0)' bbStep='OrPattern : no-match -> CatchClause(+2)' nonSimple='CatchClause -V MyError -^ MemberAccessExpr -> isZero -> Argument -V x -^ CallExpr -? MyError -^ MemberAccessExpr -^ ConditionalPattern -^ OrPattern'
+    return 0
+  } catch MyError.error3(let withParam) { // $ bbStep='CallExpr : match -> Block(+0)' bbStep='CallExpr : no-match -> CatchClause(+2)'
+    return withParam
+  } catch is MyError { // $ bbStep=' : match -> Block(+0)' bbStep=' : no-match -> CatchClause(+2)'
+    print("MyError") // $ bbStep='CallExpr : successor -> 0(+4)'
   } catch {
-    print("Unknown error \(error)") // $ noCfg
+    print("Unknown error \(error)") // $ bbStep='CallExpr : successor -> 0(+2)'
   }
   return 0
 }
@@ -395,7 +395,7 @@ class Derived : C { // $ nonSimple='ClassLikeDeclaration -V Derived -^ BaseType
 
 func doWithoutCatch(x : Int) throws -> Int {
   do {
-    try mightThrow(x: 0)
+    try mightThrow(x: 0) // $ bbStep='CallExpr : successor -> try(+0)'
     print("Did not throw.")
     try! mightThrow(x: 0)
     print("Still did not throw.")