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.

Author: DanielRosenwasser

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") { 
@@ -55,15 +55,15 @@ function f2() {
 >1 : 1
     }
     catch (e) {
->e : any
+>e : unknown
 
         x = 2;
 >x = 2 : 2
 >x : 0 | 1 | 2 | 3
 >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
 }
 
 /**