Add codefix for 'convert to unknown' diagnostic

Codefix for diagnostic error 2352: "Conversion of type '{0}' to type '{1}' may be
a mistake because neither type sufficiently overlaps with the other. If this was
intentional, convert the expression to 'unknown' first."

Add codefix for both AsExpressions and TypeAssertions

src/compiler/diagnosticMessages.json

@@ -4724,5 +4724,13 @@
     "Generate types for all packages without types": {
         "category": "Message",
         "code": 95068
+    },
+    "Add 'unknown' conversion for non-overlapping types": {
+        "category": "Message",
+        "code": 95069
+    },
+    "Add 'unknown' to all conversions of non-overlapping types": {
+        "category": "Message",
+        "code": 95070
     }
 }

src/services/codefixes/addConvertToUnknownForNonOverlappingTypes.ts

@@ -0,0 +1,42 @@
+/* @internal */
+namespace ts.codefix {
+    const fixId = "addConvertToUnknownForNonOverlappingTypes";
+    const errorCodes = [Diagnostics.Conversion_of_type_0_to_type_1_may_be_a_mistake_because_neither_type_sufficiently_overlaps_with_the_other_If_this_was_intentional_convert_the_expression_to_unknown_first.code];
+    registerCodeFix({
+        errorCodes,
+        getCodeActions: (context) => {
+            const changes = textChanges.ChangeTracker.with(context, t => makeChange(t, context.sourceFile, context.span.start));
+            return [createCodeFixAction(fixId, changes, Diagnostics.Add_unknown_conversion_for_non_overlapping_types, fixId, Diagnostics.Add_unknown_to_all_conversions_of_non_overlapping_types)];
+        },
+        fixIds: [fixId],
+        getAllCodeActions: context => codeFixAll(context, errorCodes, (changes, diag) => makeChange(changes, diag.file, diag.start)),
+    });
+
+    function makeChange(changeTracker: textChanges.ChangeTracker, sourceFile: SourceFile, pos: number) {
+        const token = getTokenAtPosition(sourceFile, pos);
+
+        const asExpression = findAncestor<AsExpression>(token, isAsExpression)!;
+        if (!!asExpression) {
+            Debug.assert(!!asExpression, "Expected position to be owned by an as-expression.");
+
+            const nodeBeingCast = asExpression.getChildAt(0);
+            const expressionBeingCast = findAncestor<Expression>(nodeBeingCast, isExpression)!;
+            Debug.assert(!!expressionBeingCast, "Expected position to be owned by an expression.");
+
+            const replacement = createAsExpression(expressionBeingCast, createKeywordTypeNode(SyntaxKind.UnknownKeyword));
+            changeTracker.replaceNode(sourceFile, expressionBeingCast, replacement);
+        }
+
+        const typeAssertion = findAncestor<TypeAssertion>(token, isTypeAssertion)!;
+        if (!!typeAssertion) {
+            Debug.assert(!!typeAssertion, "Expected position to be owned by a type assertion.");
+
+            const nodeBeingCast = typeAssertion.getLastToken();
+            const expressionBeingCast = findAncestor<Expression>(nodeBeingCast, isExpression)!;
+            Debug.assert(!!expressionBeingCast, "Expected position to be owned by an expression.");
+
+            const replacement = createTypeAssertion(createKeywordTypeNode(SyntaxKind.UnknownKeyword), expressionBeingCast);
+            changeTracker.replaceNode(sourceFile, expressionBeingCast, replacement);
+        }
+    }
+}

src/services/tsconfig.json

@@ -43,6 +43,7 @@
         "textChanges.ts",
         "codeFixProvider.ts",
         "refactorProvider.ts",
+        "codefixes/addConvertToUnknownForNonOverlappingTypes.ts",
         "codefixes/addMissingInvocationForDecorator.ts",
         "codefixes/annotateWithTypeFromJSDoc.ts",
         "codefixes/convertFunctionToEs6Class.ts",