Add flag to change catch variables' default types to unknown (#41013)

* Add test case for 'useUnknownInCatchVariables'.

* Add new 'useUnknownInCatchVariables' flag.

* Accepted baselines.

* Add test for catch variable explicitly typed as 'any'.

* Accepted baselines.

* Move option under 'strict'.

* Accepted baselines.

* 'useUnknownInCatchVariables' is strict in command line help.

src/compiler/checker.ts

@@ -346,6 +346,7 @@ namespace ts {
         const strictOptionalProperties = getStrictOptionValue(compilerOptions, "strictOptionalProperties");
         const noImplicitAny = getStrictOptionValue(compilerOptions, "noImplicitAny");
         const noImplicitThis = getStrictOptionValue(compilerOptions, "noImplicitThis");
+        const useUnknownInCatchVariables = getStrictOptionValue(compilerOptions, "useUnknownInCatchVariables");
         const keyofStringsOnly = !!compilerOptions.keyofStringsOnly;
         const freshObjectLiteralFlag = compilerOptions.suppressExcessPropertyErrors ? 0 : ObjectFlags.FreshLiteral;
 
@@ -9012,7 +9013,7 @@ namespace ts {
             if (isCatchClauseVariableDeclarationOrBindingElement(declaration)) {
                 const typeNode = getEffectiveTypeAnnotationNode(declaration);
                 if (typeNode === undefined) {
-                    return anyType;
+                    return useUnknownInCatchVariables ? unknownType : anyType;
                 }
                 const type = getTypeOfNode(typeNode);
                 // an errorType will make `checkTryStatement` issue an error

src/compiler/commandLineParser.ts

@@ -632,6 +632,15 @@ namespace ts {
             category: Diagnostics.Type_Checking,
             description: Diagnostics.Raise_error_on_this_expressions_with_an_implied_any_type,
         },
+        {
+            name: "useUnknownInCatchVariables",
+            type: "boolean",
+            affectsSemanticDiagnostics: true,
+            strictFlag: true,
+            showInSimplifiedHelpView: true,
+            category: Diagnostics.Type_Checking,
+            description: Diagnostics.Type_catch_clause_variables_as_unknown_instead_of_any,
+        },
         {
             name: "alwaysStrict",
             type: "boolean",

src/compiler/diagnosticMessages.json

@@ -5198,6 +5198,10 @@
         "category": "Message",
         "code": 6802
     },
+    "Type catch clause variables as 'unknown' instead of 'any'.": {
+        "category": "Message",
+        "code": 6803
+    },
  
     "Variable '{0}' implicitly has an '{1}' type.": {
         "category": "Error",

src/compiler/types.ts

@@ -6048,6 +6048,7 @@ namespace ts {
         /* @internal */ suppressOutputPathCheck?: boolean;
         target?: ScriptTarget; // TODO: GH#18217 frequently asserted as defined
         traceResolution?: boolean;
+        useUnknownInCatchVariables?: boolean;
         resolveJsonModule?: boolean;
         types?: string[];
         /** Paths used to compute primary types search locations */

src/compiler/utilities.ts

@@ -6088,6 +6088,7 @@ namespace ts {
         | "strictPropertyInitialization"
         | "strictOptionalProperties"
         | "alwaysStrict"
+        | "useUnknownInCatchVariables"
         ;
 
     export function getStrictOptionValue(compilerOptions: CompilerOptions, flag: StrictOptionName): boolean {

tests/baselines/reference/api/tsserverlibrary.d.ts

@@ -2919,6 +2919,7 @@ declare namespace ts {
         suppressImplicitAnyIndexErrors?: boolean;
         target?: ScriptTarget;
         traceResolution?: boolean;
+        useUnknownInCatchVariables?: boolean;
         resolveJsonModule?: boolean;
         types?: string[];
         /** Paths used to compute primary types search locations */

tests/baselines/reference/api/typescript.d.ts

@@ -2919,6 +2919,7 @@ declare namespace ts {
         suppressImplicitAnyIndexErrors?: boolean;
         target?: ScriptTarget;
         traceResolution?: boolean;
+        useUnknownInCatchVariables?: boolean;
         resolveJsonModule?: boolean;
         types?: string[];
         /** Paths used to compute primary types search locations */

tests/baselines/reference/controlFlowForCatchAndFinally.types

@@ -120,7 +120,7 @@ class Foo {
 >Aborter : typeof Aborter
 
         } catch (error) {
->error : any
+>error : unknown
 
             if (this.abortController !== undefined) {
 >this.abortController !== undefined : boolean

tests/baselines/reference/showConfig/Shows tsconfig for single option/useUnknownInCatchVariables/tsconfig.json

@@ -0,0 +1,5 @@
+{
+    "compilerOptions": {
+        "useUnknownInCatchVariables": true
+    }
+}

tests/baselines/reference/tryCatchFinallyControlFlow.types

@@ -19,10 +19,10 @@ function f1() {
 >a : number
     }
     catch (e) {
->e : any
+>e : unknown
 
         throw e;
->e : any
+>e : unknown
     }
     finally {
         if (a != null && a.toFixed(0) == "123") { 
@@ -55,7 +55,7 @@ function f2() {
 >1 : 1
     }
     catch (e) {
->e : any
+>e : unknown
 
         x = 2;
 >x = 2 : 2
@@ -63,7 +63,7 @@ function f2() {
 >2 : 2
 
         throw e;
->e : any
+>e : unknown
     }
     finally {
         x;  // 0 | 1 | 2
@@ -87,7 +87,7 @@ function f3() {
 >1 : 1
     }
     catch (e) {
->e : any
+>e : unknown
 
         x = 2;
 >x = 2 : 2
@@ -118,7 +118,7 @@ function f4() {
 >1 : 1
     }
     catch (e) {
->e : any
+>e : unknown
 
         x = 2;
 >x = 2 : 2
@@ -149,7 +149,7 @@ function f5() {
         return;
     }
     catch (e) {
->e : any
+>e : unknown
 
         x = 2;
 >x = 2 : 2
@@ -178,7 +178,7 @@ function f6() {
 >1 : 1
     }
     catch (e) {
->e : any
+>e : unknown
 
         x = 2;
 >x = 2 : 2
@@ -211,7 +211,7 @@ function f7() {
         return;
     }
     catch (e) {
->e : any
+>e : unknown
 
         x = 2;
 >x = 2 : 2
@@ -324,7 +324,7 @@ function f10() {
             return;
         }
         catch (e) {
->e : any
+>e : unknown
 
             x = 2;
 >x = 2 : 2
@@ -388,7 +388,7 @@ function f11() {
             }
         }
         catch (e) {
->e : any
+>e : unknown
 
             x;  // 0 | 1 | 2
 >x : 0 | 1 | 2
@@ -466,7 +466,7 @@ function f12() {
             }
         }
         catch (e) {
->e : any
+>e : unknown
 
             x;  // 0 | 1 | 2
 >x : 0 | 1 | 2
@@ -576,7 +576,7 @@ function t1() {
 >'x' : "x"
         }
         catch (e) {
->e : any
+>e : unknown
 
             return null;
 >null : null
@@ -626,7 +626,7 @@ function notallowed(arg: number) {
         finally { }
     }
     catch (err) {
->err : any
+>err : unknown
 
         state.tag;
 >state.tag : "one" | "two" | "three"
@@ -770,7 +770,7 @@ function f21() {
 >x : 3 | 4 | 5
     }
     catch (e) {
->e : any
+>e : unknown
 
         x;  // 0 | 1 | 2 | 3 | 4 | 5
 >x : 0 | 1 | 2 | 3 | 4 | 5

tests/baselines/reference/tsConfig/Default initialized TSConfig/tsconfig.json

@@ -81,6 +81,7 @@
     // "strictPropertyInitialization": true,             /* Enable strict checking of property initialization in classes. */
     // "strictOptionalProperties": true,                 /* Enable strict checking of optional properties. */
     // "noImplicitThis": true,                           /* Raise error on 'this' expressions with an implied 'any' type. */
+    // "useUnknownInCatchVariables": true,               /* Type catch clause variables as 'unknown' instead of 'any'. */
     // "alwaysStrict": true,                             /* Parse in strict mode and emit "use strict" for each source file. */
     // "noUnusedLocals": true,                           /* Report errors on unused locals. */
     // "noUnusedParameters": true,                       /* Report errors on unused parameters. */

tests/baselines/reference/tsConfig/Initialized TSConfig with advanced options/tsconfig.json

@@ -81,6 +81,7 @@
     // "strictPropertyInitialization": true,             /* Enable strict checking of property initialization in classes. */
     // "strictOptionalProperties": true,                 /* Enable strict checking of optional properties. */
     // "noImplicitThis": true,                           /* Raise error on 'this' expressions with an implied 'any' type. */
+    // "useUnknownInCatchVariables": true,               /* Type catch clause variables as 'unknown' instead of 'any'. */
     // "alwaysStrict": true,                             /* Parse in strict mode and emit "use strict" for each source file. */
     // "noUnusedLocals": true,                           /* Report errors on unused locals. */
     // "noUnusedParameters": true,                       /* Report errors on unused parameters. */

tests/baselines/reference/tsConfig/Initialized TSConfig with boolean value compiler options/tsconfig.json

@@ -81,6 +81,7 @@
     // "strictPropertyInitialization": true,             /* Enable strict checking of property initialization in classes. */
     // "strictOptionalProperties": true,                 /* Enable strict checking of optional properties. */
     // "noImplicitThis": true,                           /* Raise error on 'this' expressions with an implied 'any' type. */
+    // "useUnknownInCatchVariables": true,               /* Type catch clause variables as 'unknown' instead of 'any'. */
     // "alwaysStrict": true,                             /* Parse in strict mode and emit "use strict" for each source file. */
     "noUnusedLocals": true,                              /* Report errors on unused locals. */
     // "noUnusedParameters": true,                       /* Report errors on unused parameters. */

tests/baselines/reference/tsConfig/Initialized TSConfig with enum value compiler options/tsconfig.json

@@ -81,6 +81,7 @@
     // "strictPropertyInitialization": true,             /* Enable strict checking of property initialization in classes. */
     // "strictOptionalProperties": true,                 /* Enable strict checking of optional properties. */
     // "noImplicitThis": true,                           /* Raise error on 'this' expressions with an implied 'any' type. */
+    // "useUnknownInCatchVariables": true,               /* Type catch clause variables as 'unknown' instead of 'any'. */
     // "alwaysStrict": true,                             /* Parse in strict mode and emit "use strict" for each source file. */
     // "noUnusedLocals": true,                           /* Report errors on unused locals. */
     // "noUnusedParameters": true,                       /* Report errors on unused parameters. */

tests/baselines/reference/tsConfig/Initialized TSConfig with files options/tsconfig.json

@@ -81,6 +81,7 @@
     // "strictPropertyInitialization": true,             /* Enable strict checking of property initialization in classes. */
     // "strictOptionalProperties": true,                 /* Enable strict checking of optional properties. */
     // "noImplicitThis": true,                           /* Raise error on 'this' expressions with an implied 'any' type. */
+    // "useUnknownInCatchVariables": true,               /* Type catch clause variables as 'unknown' instead of 'any'. */
     // "alwaysStrict": true,                             /* Parse in strict mode and emit "use strict" for each source file. */
     // "noUnusedLocals": true,                           /* Report errors on unused locals. */
     // "noUnusedParameters": true,                       /* Report errors on unused parameters. */

tests/baselines/reference/tsConfig/Initialized TSConfig with incorrect compiler option value/tsconfig.json

@@ -81,6 +81,7 @@
     // "strictPropertyInitialization": true,             /* Enable strict checking of property initialization in classes. */
     // "strictOptionalProperties": true,                 /* Enable strict checking of optional properties. */
     // "noImplicitThis": true,                           /* Raise error on 'this' expressions with an implied 'any' type. */
+    // "useUnknownInCatchVariables": true,               /* Type catch clause variables as 'unknown' instead of 'any'. */
     // "alwaysStrict": true,                             /* Parse in strict mode and emit "use strict" for each source file. */
     // "noUnusedLocals": true,                           /* Report errors on unused locals. */
     // "noUnusedParameters": true,                       /* Report errors on unused parameters. */

tests/baselines/reference/tsConfig/Initialized TSConfig with incorrect compiler option/tsconfig.json

@@ -81,6 +81,7 @@
     // "strictPropertyInitialization": true,             /* Enable strict checking of property initialization in classes. */
     // "strictOptionalProperties": true,                 /* Enable strict checking of optional properties. */
     // "noImplicitThis": true,                           /* Raise error on 'this' expressions with an implied 'any' type. */
+    // "useUnknownInCatchVariables": true,               /* Type catch clause variables as 'unknown' instead of 'any'. */
     // "alwaysStrict": true,                             /* Parse in strict mode and emit "use strict" for each source file. */
     // "noUnusedLocals": true,                           /* Report errors on unused locals. */
     // "noUnusedParameters": true,                       /* Report errors on unused parameters. */

tests/baselines/reference/tsConfig/Initialized TSConfig with list compiler options with enum value/tsconfig.json

@@ -81,6 +81,7 @@
     // "strictPropertyInitialization": true,             /* Enable strict checking of property initialization in classes. */
     // "strictOptionalProperties": true,                 /* Enable strict checking of optional properties. */
     // "noImplicitThis": true,                           /* Raise error on 'this' expressions with an implied 'any' type. */
+    // "useUnknownInCatchVariables": true,               /* Type catch clause variables as 'unknown' instead of 'any'. */
     // "alwaysStrict": true,                             /* Parse in strict mode and emit "use strict" for each source file. */
     // "noUnusedLocals": true,                           /* Report errors on unused locals. */
     // "noUnusedParameters": true,                       /* Report errors on unused parameters. */

tests/baselines/reference/tsConfig/Initialized TSConfig with list compiler options/tsconfig.json

@@ -81,6 +81,7 @@
     // "strictPropertyInitialization": true,             /* Enable strict checking of property initialization in classes. */
     // "strictOptionalProperties": true,                 /* Enable strict checking of optional properties. */
     // "noImplicitThis": true,                           /* Raise error on 'this' expressions with an implied 'any' type. */
+    // "useUnknownInCatchVariables": true,               /* Type catch clause variables as 'unknown' instead of 'any'. */
     // "alwaysStrict": true,                             /* Parse in strict mode and emit "use strict" for each source file. */
     // "noUnusedLocals": true,                           /* Report errors on unused locals. */
     // "noUnusedParameters": true,                       /* Report errors on unused parameters. */

tests/baselines/reference/tsc/runWithoutArgs/initial-build/show-help-with-ExitStatus.DiagnosticsPresent_OutputsSkipped.js

@@ -44,6 +44,7 @@ Options:
  --strictPropertyInitialization                     Enable strict checking of property initialization in classes.
  --strictOptionalProperties                         Enable strict checking of optional properties.
  --noImplicitThis                                   Raise error on 'this' expressions with an implied 'any' type.
+ --useUnknownInCatchVariables                       Type catch clause variables as 'unknown' instead of 'any'.
  --alwaysStrict                                     Parse in strict mode and emit "use strict" for each source file.
  --noUnusedLocals                                   Report errors on unused locals.
  --noUnusedParameters                               Report errors on unused parameters.

tests/baselines/reference/tscWatch/programUpdates/should-not-trigger-recompilation-because-of-program-emit/declarationDir-is-specified.js

@@ -102,6 +102,7 @@ interface Array<T> { length: number; [n: number]: T; }
     // "strictPropertyInitialization": true,             /* Enable strict checking of property initialization in classes. */
     // "strictOptionalProperties": true,                 /* Enable strict checking of optional properties. */
     // "noImplicitThis": true,                           /* Raise error on 'this' expressions with an implied 'any' type. */
+    // "useUnknownInCatchVariables": true,               /* Type catch clause variables as 'unknown' instead of 'any'. */
     // "alwaysStrict": true,                             /* Parse in strict mode and emit "use strict" for each source file. */
     // "noUnusedLocals": true,                           /* Report errors on unused locals. */
     // "noUnusedParameters": true,                       /* Report errors on unused parameters. */

tests/baselines/reference/tscWatch/programUpdates/should-not-trigger-recompilation-because-of-program-emit/when-outDir-and-declarationDir-is-specified.js

@@ -102,6 +102,7 @@ interface Array<T> { length: number; [n: number]: T; }
     // "strictPropertyInitialization": true,             /* Enable strict checking of property initialization in classes. */
     // "strictOptionalProperties": true,                 /* Enable strict checking of optional properties. */
     // "noImplicitThis": true,                           /* Raise error on 'this' expressions with an implied 'any' type. */
+    // "useUnknownInCatchVariables": true,               /* Type catch clause variables as 'unknown' instead of 'any'. */
     // "alwaysStrict": true,                             /* Parse in strict mode and emit "use strict" for each source file. */
     // "noUnusedLocals": true,                           /* Report errors on unused locals. */
     // "noUnusedParameters": true,                       /* Report errors on unused parameters. */

tests/baselines/reference/tscWatch/programUpdates/should-not-trigger-recompilation-because-of-program-emit/when-outDir-is-specified.js

@@ -102,6 +102,7 @@ interface Array<T> { length: number; [n: number]: T; }
     // "strictPropertyInitialization": true,             /* Enable strict checking of property initialization in classes. */
     // "strictOptionalProperties": true,                 /* Enable strict checking of optional properties. */
     // "noImplicitThis": true,                           /* Raise error on 'this' expressions with an implied 'any' type. */
+    // "useUnknownInCatchVariables": true,               /* Type catch clause variables as 'unknown' instead of 'any'. */
     // "alwaysStrict": true,                             /* Parse in strict mode and emit "use strict" for each source file. */
     // "noUnusedLocals": true,                           /* Report errors on unused locals. */
     // "noUnusedParameters": true,                       /* Report errors on unused parameters. */

tests/baselines/reference/tscWatch/programUpdates/should-not-trigger-recompilation-because-of-program-emit/with-outFile.js

@@ -102,6 +102,7 @@ interface Array<T> { length: number; [n: number]: T; }
     // "strictPropertyInitialization": true,             /* Enable strict checking of property initialization in classes. */
     // "strictOptionalProperties": true,                 /* Enable strict checking of optional properties. */
     // "noImplicitThis": true,                           /* Raise error on 'this' expressions with an implied 'any' type. */
+    // "useUnknownInCatchVariables": true,               /* Type catch clause variables as 'unknown' instead of 'any'. */
     // "alwaysStrict": true,                             /* Parse in strict mode and emit "use strict" for each source file. */
     // "noUnusedLocals": true,                           /* Report errors on unused locals. */
     // "noUnusedParameters": true,                       /* Report errors on unused parameters. */

tests/baselines/reference/tscWatch/programUpdates/should-not-trigger-recompilation-because-of-program-emit/without-outDir-or-outFile-is-specified-with-declaration-enabled.js

@@ -102,6 +102,7 @@ interface Array<T> { length: number; [n: number]: T; }
     // "strictPropertyInitialization": true,             /* Enable strict checking of property initialization in classes. */
     // "strictOptionalProperties": true,                 /* Enable strict checking of optional properties. */
     // "noImplicitThis": true,                           /* Raise error on 'this' expressions with an implied 'any' type. */
+    // "useUnknownInCatchVariables": true,               /* Type catch clause variables as 'unknown' instead of 'any'. */
     // "alwaysStrict": true,                             /* Parse in strict mode and emit "use strict" for each source file. */
     // "noUnusedLocals": true,                           /* Report errors on unused locals. */
     // "noUnusedParameters": true,                       /* Report errors on unused parameters. */

tests/baselines/reference/tscWatch/programUpdates/should-not-trigger-recompilation-because-of-program-emit/without-outDir-or-outFile-is-specified.js

@@ -102,6 +102,7 @@ interface Array<T> { length: number; [n: number]: T; }
     // "strictPropertyInitialization": true,             /* Enable strict checking of property initialization in classes. */
     // "strictOptionalProperties": true,                 /* Enable strict checking of optional properties. */
     // "noImplicitThis": true,                           /* Raise error on 'this' expressions with an implied 'any' type. */
+    // "useUnknownInCatchVariables": true,               /* Type catch clause variables as 'unknown' instead of 'any'. */
     // "alwaysStrict": true,                             /* Parse in strict mode and emit "use strict" for each source file. */
     // "noUnusedLocals": true,                           /* Report errors on unused locals. */
     // "noUnusedParameters": true,                       /* Report errors on unused parameters. */

tests/baselines/reference/typedefOnStatements.types

@@ -68,7 +68,7 @@ throw new Error('Unreachable')
 try {
 }
 catch (e) {
->e : any
+>e : unknown
 }
 
 /**

tests/baselines/reference/useUnknownInCatchVariables01.errors.txt

@@ -0,0 +1,47 @@
+tests/cases/compiler/useUnknownInCatchVariables01.ts(6,12): error TS2339: Property 'toUpperCase' does not exist on type 'unknown'.
+tests/cases/compiler/useUnknownInCatchVariables01.ts(7,10): error TS2356: An arithmetic operand must be of type 'any', 'number', 'bigint' or an enum type.
+tests/cases/compiler/useUnknownInCatchVariables01.ts(8,10): error TS2349: This expression is not callable.
+  Type '{}' has no call signatures.
+
+
+==== tests/cases/compiler/useUnknownInCatchVariables01.ts (3 errors) ====
+    try {
+        // ...
+    }
+    catch (e) {
+        // error!
+        void e.toUpperCase();
+               ~~~~~~~~~~~
+!!! error TS2339: Property 'toUpperCase' does not exist on type 'unknown'.
+        void e++;
+             ~
+!!! error TS2356: An arithmetic operand must be of type 'any', 'number', 'bigint' or an enum type.
+        void e();
+             ~
+!!! error TS2349: This expression is not callable.
+!!! error TS2349:   Type '{}' has no call signatures.
+    
+        if (typeof e === "string") {
+            // works!
+            // We've narrowed 'e' down to the type 'string'.
+            console.log(e.toUpperCase());
+        }
+        if (e instanceof Error) {
+            e.stack?.toUpperCase();
+        }
+        if (typeof e === "number") {
+            e.toExponential();
+            e++;
+        }
+    }
+    
+    
+    try {
+        // ...
+    }
+    catch (e: any) {
+        // All are allowed.
+        void e.toUpperCase();
+        void e.toExponential();
+        void e();
+    }

tests/baselines/reference/useUnknownInCatchVariables01.js

@@ -0,0 +1,67 @@
+//// [useUnknownInCatchVariables01.ts]
+try {
+    // ...
+}
+catch (e) {
+    // error!
+    void e.toUpperCase();
+    void e++;
+    void e();
+
+    if (typeof e === "string") {
+        // works!
+        // We've narrowed 'e' down to the type 'string'.
+        console.log(e.toUpperCase());
+    }
+    if (e instanceof Error) {
+        e.stack?.toUpperCase();
+    }
+    if (typeof e === "number") {
+        e.toExponential();
+        e++;
+    }
+}
+
+
+try {
+    // ...
+}
+catch (e: any) {
+    // All are allowed.
+    void e.toUpperCase();
+    void e.toExponential();
+    void e();
+}
+
+//// [useUnknownInCatchVariables01.js]
+var _a;
+try {
+    // ...
+}
+catch (e) {
+    // error!
+    void e.toUpperCase();
+    void e++;
+    void e();
+    if (typeof e === "string") {
+        // works!
+        // We've narrowed 'e' down to the type 'string'.
+        console.log(e.toUpperCase());
+    }
+    if (e instanceof Error) {
+        (_a = e.stack) === null || _a === void 0 ? void 0 : _a.toUpperCase();
+    }
+    if (typeof e === "number") {
+        e.toExponential();
+        e++;
+    }
+}
+try {
+    // ...
+}
+catch (e) {
+    // All are allowed.
+    void e.toUpperCase();
+    void e.toExponential();
+    void e();
+}

tests/baselines/reference/useUnknownInCatchVariables01.symbols

@@ -0,0 +1,71 @@
+=== tests/cases/compiler/useUnknownInCatchVariables01.ts ===
+try {
+    // ...
+}
+catch (e) {
+>e : Symbol(e, Decl(useUnknownInCatchVariables01.ts, 3, 7))
+
+    // error!
+    void e.toUpperCase();
+>e : Symbol(e, Decl(useUnknownInCatchVariables01.ts, 3, 7))
+
+    void e++;
+>e : Symbol(e, Decl(useUnknownInCatchVariables01.ts, 3, 7))
+
+    void e();
+>e : Symbol(e, Decl(useUnknownInCatchVariables01.ts, 3, 7))
+
+    if (typeof e === "string") {
+>e : Symbol(e, Decl(useUnknownInCatchVariables01.ts, 3, 7))
+
+        // works!
+        // We've narrowed 'e' down to the type 'string'.
+        console.log(e.toUpperCase());
+>console.log : Symbol(Console.log, Decl(lib.dom.d.ts, --, --))
+>console : Symbol(console, Decl(lib.dom.d.ts, --, --))
+>log : Symbol(Console.log, Decl(lib.dom.d.ts, --, --))
+>e.toUpperCase : Symbol(String.toUpperCase, Decl(lib.es5.d.ts, --, --))
+>e : Symbol(e, Decl(useUnknownInCatchVariables01.ts, 3, 7))
+>toUpperCase : Symbol(String.toUpperCase, Decl(lib.es5.d.ts, --, --))
+    }
+    if (e instanceof Error) {
+>e : Symbol(e, Decl(useUnknownInCatchVariables01.ts, 3, 7))
+>Error : Symbol(Error, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
+
+        e.stack?.toUpperCase();
+>e.stack?.toUpperCase : Symbol(String.toUpperCase, Decl(lib.es5.d.ts, --, --))
+>e.stack : Symbol(Error.stack, Decl(lib.es5.d.ts, --, --))
+>e : Symbol(e, Decl(useUnknownInCatchVariables01.ts, 3, 7))
+>stack : Symbol(Error.stack, Decl(lib.es5.d.ts, --, --))
+>toUpperCase : Symbol(String.toUpperCase, Decl(lib.es5.d.ts, --, --))
+    }
+    if (typeof e === "number") {
+>e : Symbol(e, Decl(useUnknownInCatchVariables01.ts, 3, 7))
+
+        e.toExponential();
+>e.toExponential : Symbol(Number.toExponential, Decl(lib.es5.d.ts, --, --))
+>e : Symbol(e, Decl(useUnknownInCatchVariables01.ts, 3, 7))
+>toExponential : Symbol(Number.toExponential, Decl(lib.es5.d.ts, --, --))
+
+        e++;
+>e : Symbol(e, Decl(useUnknownInCatchVariables01.ts, 3, 7))
+    }
+}
+
+
+try {
+    // ...
+}
+catch (e: any) {
+>e : Symbol(e, Decl(useUnknownInCatchVariables01.ts, 27, 7))
+
+    // All are allowed.
+    void e.toUpperCase();
+>e : Symbol(e, Decl(useUnknownInCatchVariables01.ts, 27, 7))
+
+    void e.toExponential();
+>e : Symbol(e, Decl(useUnknownInCatchVariables01.ts, 27, 7))
+
+    void e();
+>e : Symbol(e, Decl(useUnknownInCatchVariables01.ts, 27, 7))
+}

tests/baselines/reference/useUnknownInCatchVariables01.types

@@ -0,0 +1,101 @@
+=== tests/cases/compiler/useUnknownInCatchVariables01.ts ===
+try {
+    // ...
+}
+catch (e) {
+>e : unknown
+
+    // error!
+    void e.toUpperCase();
+>void e.toUpperCase() : undefined
+>e.toUpperCase() : any
+>e.toUpperCase : any
+>e : unknown
+>toUpperCase : any
+
+    void e++;
+>void e++ : undefined
+>e++ : number
+>e : unknown
+
+    void e();
+>void e() : undefined
+>e() : any
+>e : unknown
+
+    if (typeof e === "string") {
+>typeof e === "string" : boolean
+>typeof e : "string" | "number" | "bigint" | "boolean" | "symbol" | "undefined" | "object" | "function"
+>e : unknown
+>"string" : "string"
+
+        // works!
+        // We've narrowed 'e' down to the type 'string'.
+        console.log(e.toUpperCase());
+>console.log(e.toUpperCase()) : void
+>console.log : (...data: any[]) => void
+>console : Console
+>log : (...data: any[]) => void
+>e.toUpperCase() : string
+>e.toUpperCase : () => string
+>e : string
+>toUpperCase : () => string
+    }
+    if (e instanceof Error) {
+>e instanceof Error : boolean
+>e : unknown
+>Error : ErrorConstructor
+
+        e.stack?.toUpperCase();
+>e.stack?.toUpperCase() : string
+>e.stack?.toUpperCase : () => string
+>e.stack : string
+>e : Error
+>stack : string
+>toUpperCase : () => string
+    }
+    if (typeof e === "number") {
+>typeof e === "number" : boolean
+>typeof e : "string" | "number" | "bigint" | "boolean" | "symbol" | "undefined" | "object" | "function"
+>e : unknown
+>"number" : "number"
+
+        e.toExponential();
+>e.toExponential() : string
+>e.toExponential : (fractionDigits?: number) => string
+>e : number
+>toExponential : (fractionDigits?: number) => string
+
+        e++;
+>e++ : number
+>e : number
+    }
+}
+
+
+try {
+    // ...
+}
+catch (e: any) {
+>e : any
+
+    // All are allowed.
+    void e.toUpperCase();
+>void e.toUpperCase() : undefined
+>e.toUpperCase() : any
+>e.toUpperCase : any
+>e : any
+>toUpperCase : any
+
+    void e.toExponential();
+>void e.toExponential() : undefined
+>e.toExponential() : any
+>e.toExponential : any
+>e : any
+>toExponential : any
+
+    void e();
+>void e() : undefined
+>e() : any
+>e : any
+}

tests/cases/compiler/useUnknownInCatchVariables01.ts

@@ -0,0 +1,35 @@
+// @useUnknownInCatchVariables: true
+
+try {
+    // ...
+}
+catch (e) {
+    // error!
+    void e.toUpperCase();
+    void e++;
+    void e();
+
+    if (typeof e === "string") {
+        // works!
+        // We've narrowed 'e' down to the type 'string'.
+        console.log(e.toUpperCase());
+    }
+    if (e instanceof Error) {
+        e.stack?.toUpperCase();
+    }
+    if (typeof e === "number") {
+        e.toExponential();
+        e++;
+    }
+}
+
+
+try {
+    // ...
+}
+catch (e: any) {
+    // All are allowed.
+    void e.toUpperCase();
+    void e.toExponential();
+    void e();
+}