feat: Implement the implicitUnknown complier flag

Author: ExE-Boss

src/compiler/checker.ts

@@ -396,6 +396,13 @@ namespace ts {
             category: Diagnostics.Strict_Type_Checking_Options,
             description: Diagnostics.Raise_error_on_expressions_and_declarations_with_an_implied_any_type
         },
+        {
+            name: "implicitUnknown",
+            type: "boolean",
+            showInSimplifiedHelpView: true,
+            category: Diagnostics.Strict_Type_Checking_Options,
+            description: Diagnostics.Use_unknown_as_implicit_type
+        },
         {
             name: "strictNullChecks",
             type: "boolean",

src/compiler/commandLineParser.ts

@@ -3899,6 +3899,10 @@
         "category": "Message",
         "code": 6217
     },
+    "Use unknown as implicit type.": {
+        "category": "Message",
+        "code": 6218
+    },
 
     "Projects to reference": {
         "category": "Message",

src/compiler/diagnosticMessages.json

@@ -4605,6 +4605,8 @@ namespace ts {
         experimentalDecorators?: boolean;
         forceConsistentCasingInFileNames?: boolean;
         /*@internal*/help?: boolean;
+        /** Changes the implicit type from `any` to `unknown`. */
+        implicitUnknown?: boolean;
         importHelpers?: boolean;
         /*@internal*/init?: boolean;
         inlineSourceMap?: boolean;

src/compiler/types.ts

@@ -2956,6 +2956,8 @@ namespace ts.server.protocol {
         emitDecoratorMetadata?: boolean;
         experimentalDecorators?: boolean;
         forceConsistentCasingInFileNames?: boolean;
+        /** Changes the implicit type from `any` to `unknown`. */
+        implicitUnknown?: boolean;
         importHelpers?: boolean;
         inlineSourceMap?: boolean;
         inlineSources?: boolean;

src/server/protocol.ts

@@ -260,6 +260,10 @@ var x = 0;`, {
             options: { compilerOptions: { forceConsistentCasingInFileNames: true }, fileName: "input.js", reportDiagnostics: true }
         });
 
+        transpilesCorrectly("Supports setting 'implicitUnknown'", "x;", {
+            options: { compilerOptions: { implicitUnknown: true }, fileName: "input.js", reportDiagnostics: true }
+        });
+
         transpilesCorrectly("Supports setting 'isolatedModules'", "x;", {
             options: { compilerOptions: { isolatedModules: true }, fileName: "input.js", reportDiagnostics: true }
         });
@@ -312,6 +316,10 @@ var x = 0;`, {
             options: { compilerOptions: { noImplicitAny: true }, fileName: "input.js", reportDiagnostics: true }
         });
 
+        transpilesCorrectly("Supports setting 'noImplicitAny' and 'implicitUnknown'", "x;", {
+            options: { compilerOptions: { noImplicitAny: true, implicitUnknown: true }, fileName: "input.js", reportDiagnostics: true }
+        });
+
         transpilesCorrectly("Supports setting 'noImplicitReturns'", "x;", {
             options: { compilerOptions: { noImplicitReturns: true }, fileName: "input.js", reportDiagnostics: true }
         });