microsoft · andrewbranch · Sep 30, 2025 · Sep 29, 2025 · Sep 29, 2025
diff --git a/src/compiler/diagnosticMessages.json b/src/compiler/diagnosticMessages.json
@@ -4721,6 +4721,10 @@
         "category": "Error",
         "code": 5110
     },
+    "Visit https://aka.ms/ts6 for migration information.": {
+        "category": "Message",
+        "code": 5111
+    },
 
     "Generates a sourcemap for each corresponding '.d.ts' file.": {
         "category": "Message",

diff --git a/src/compiler/program.ts b/src/compiler/program.ts
@@ -4446,8 +4446,8 @@ export function createProgram(_rootNamesOrOptions: readonly string[] | CreatePro
     function checkDeprecations(
         deprecatedIn: string,
         removedIn: string,
-        createDiagnostic: (name: string, value: string | undefined, useInstead: string | undefined, message: DiagnosticMessage, ...args: DiagnosticArguments) => void,
-        fn: (createDeprecatedDiagnostic: (name: string, value?: string, useInstead?: string) => void) => void,
+        createDiagnostic: (name: string, value: string | undefined, useInstead: string | undefined, related: DiagnosticMessage | undefined, message: DiagnosticMessage, ...args: DiagnosticArguments) => void,
+        fn: (createDeprecatedDiagnostic: (name: string, value?: string, useInstead?: string, related?: DiagnosticMessage) => void) => void,
     ) {
         const deprecatedInVersion = new Version(deprecatedIn);
         const removedInVersion = new Version(removedIn);
@@ -4458,36 +4458,44 @@ export function createProgram(_rootNamesOrOptions: readonly string[] | CreatePro
         const canBeSilenced = !mustBeRemoved && ignoreDeprecationsVersion.compareTo(deprecatedInVersion) === Comparison.LessThan;
 
         if (mustBeRemoved || canBeSilenced) {
-            fn((name, value, useInstead) => {
+            fn((name, value, useInstead, related) => {
                 if (mustBeRemoved) {
                     if (value === undefined) {
-                        createDiagnostic(name, value, useInstead, Diagnostics.Option_0_has_been_removed_Please_remove_it_from_your_configuration, name);
+                        createDiagnostic(name, value, useInstead, related, Diagnostics.Option_0_has_been_removed_Please_remove_it_from_your_configuration, name);
                     }
                     else {
-                        createDiagnostic(name, value, useInstead, Diagnostics.Option_0_1_has_been_removed_Please_remove_it_from_your_configuration, name, value);
+                        createDiagnostic(name, value, useInstead, related, Diagnostics.Option_0_1_has_been_removed_Please_remove_it_from_your_configuration, name, value);
                     }
                 }
                 else {
                     if (value === undefined) {
-                        createDiagnostic(name, value, useInstead, Diagnostics.Option_0_is_deprecated_and_will_stop_functioning_in_TypeScript_1_Specify_compilerOption_ignoreDeprecations_Colon_2_to_silence_this_error, name, removedIn, deprecatedIn);
+                        createDiagnostic(name, value, useInstead, related, Diagnostics.Option_0_is_deprecated_and_will_stop_functioning_in_TypeScript_1_Specify_compilerOption_ignoreDeprecations_Colon_2_to_silence_this_error, name, removedIn, deprecatedIn);
                     }
                     else {
-                        createDiagnostic(name, value, useInstead, Diagnostics.Option_0_1_is_deprecated_and_will_stop_functioning_in_TypeScript_2_Specify_compilerOption_ignoreDeprecations_Colon_3_to_silence_this_error, name, value, removedIn, deprecatedIn);
+                        createDiagnostic(name, value, useInstead, related, Diagnostics.Option_0_1_is_deprecated_and_will_stop_functioning_in_TypeScript_2_Specify_compilerOption_ignoreDeprecations_Colon_3_to_silence_this_error, name, value, removedIn, deprecatedIn);
                     }
                 }
             });
         }
     }
 
     function verifyDeprecatedCompilerOptions() {
-        function createDiagnostic(name: string, value: string | undefined, useInstead: string | undefined, message: DiagnosticMessage, ...args: DiagnosticArguments) {
+        function createDiagnostic(name: string, value: string | undefined, useInstead: string | undefined, related: DiagnosticMessage | undefined, message: DiagnosticMessage, ...args: DiagnosticArguments) {
             if (useInstead) {
-                const details = chainDiagnosticMessages(/*details*/ undefined, Diagnostics.Use_0_instead, useInstead);
+                let details = chainDiagnosticMessages(/*details*/ undefined, Diagnostics.Use_0_instead, useInstead);
+                if (related) {
+                    details = chainDiagnosticMessages(details, related);
+                }
                 const chain = chainDiagnosticMessages(details, message, ...args);
                 createDiagnosticForOption(/*onKey*/ !value, name, /*option2*/ undefined, chain);
             }
             else {
-                createDiagnosticForOption(/*onKey*/ !value, name, /*option2*/ undefined, message, ...args);
+                let details: DiagnosticMessageChain | undefined;
+                if (related) {
+                    details = chainDiagnosticMessages(/*details*/ undefined, related);
+                }
+                const chain = chainDiagnosticMessages(details, message, ...args);
+                createDiagnosticForOption(/*onKey*/ !value, name, /*option2*/ undefined, chain);
             }
         }
 
@@ -4526,13 +4534,16 @@ export function createProgram(_rootNamesOrOptions: readonly string[] | CreatePro
 
         checkDeprecations("6.0", "7.0", createDiagnostic, createDeprecatedDiagnostic => {
             if (options.moduleResolution === ModuleResolutionKind.Node10) {
-                createDeprecatedDiagnostic("moduleResolution", "node10");
+                createDeprecatedDiagnostic("moduleResolution", "node10", /*useInstead*/ undefined, Diagnostics.Visit_https_Colon_Slash_Slashaka_ms_Slashts6_for_migration_information);
+            }
+            if (options.baseUrl !== undefined) {
+                createDeprecatedDiagnostic("baseUrl", /*value*/ undefined, /*useInstead*/ undefined, Diagnostics.Visit_https_Colon_Slash_Slashaka_ms_Slashts6_for_migration_information);
             }
         });
     }
 
     function verifyDeprecatedProjectReference(ref: ProjectReference, parentFile: JsonSourceFile | undefined, index: number) {
-        function createDiagnostic(_name: string, _value: string | undefined, _useInstead: string | undefined, message: DiagnosticMessage, ...args: DiagnosticArguments) {
+        function createDiagnostic(_name: string, _value: string | undefined, _useInstead: string | undefined, _related: DiagnosticMessage | undefined, message: DiagnosticMessage, ...args: DiagnosticArguments) {
             createDiagnosticForReference(parentFile, index, message, ...args);
         }
 

diff --git a/src/compiler/types.ts b/src/compiler/types.ts
@@ -7410,6 +7410,7 @@ export interface CompilerOptions {
     allowUnreachableCode?: boolean;
     allowUnusedLabels?: boolean;
     alwaysStrict?: boolean; // Always combine with strict property
+    /** @deprecated */
     baseUrl?: string;
     /**
      * An error if set - this should only go through the -b pipeline and not actually be observed

diff --git a/tests/baselines/reference/amdModuleConstEnumUsage.errors.txt b/tests/baselines/reference/amdModuleConstEnumUsage.errors.txt
@@ -0,0 +1,19 @@
+error TS5101: Option 'baseUrl' is deprecated and will stop functioning in TypeScript 7.0. Specify compilerOption '"ignoreDeprecations": "6.0"' to silence this error.
+  Visit https://aka.ms/ts6 for migration information.
+
+
+!!! error TS5101: Option 'baseUrl' is deprecated and will stop functioning in TypeScript 7.0. Specify compilerOption '"ignoreDeprecations": "6.0"' to silence this error.
+!!! error TS5101:   Visit https://aka.ms/ts6 for migration information.
+==== /proj/defs/cc.ts (0 errors) ====
+    export const enum CharCode {
+        A,
+        B
+    }
+==== /proj/component/file.ts (0 errors) ====
+    import { CharCode } from 'defs/cc';
+    export class User {
+        method(input: number) {
+            if (CharCode.A === input) {}
+        }
+    }
+
diff --git a/tests/baselines/reference/api/typescript.d.ts b/tests/baselines/reference/api/typescript.d.ts
@@ -7024,6 +7024,7 @@ declare namespace ts {
         allowUnreachableCode?: boolean;
         allowUnusedLabels?: boolean;
         alwaysStrict?: boolean;
+        /** @deprecated */
         baseUrl?: string;
         /** @deprecated */
         charset?: string;

diff --git a/tests/baselines/reference/declarationEmitMonorepoBaseUrl.errors.txt b/tests/baselines/reference/declarationEmitMonorepoBaseUrl.errors.txt
@@ -0,0 +1,59 @@
+/tsconfig.json(6,5): error TS5101: Option 'baseUrl' is deprecated and will stop functioning in TypeScript 7.0. Specify compilerOption '"ignoreDeprecations": "6.0"' to silence this error.
+  Visit https://aka.ms/ts6 for migration information.
+
+
+==== /tsconfig.json (1 errors) ====
+    {
+      "compilerOptions": {
+        "module": "nodenext",
+        "declaration": true,
+        "outDir": "temp",
+        "baseUrl": "."
+        ~~~~~~~~~
+!!! error TS5101: Option 'baseUrl' is deprecated and will stop functioning in TypeScript 7.0. Specify compilerOption '"ignoreDeprecations": "6.0"' to silence this error.
+!!! error TS5101:   Visit https://aka.ms/ts6 for migration information.
+      }
+    }
+
+==== /packages/compiler-core/src/index.ts (0 errors) ====
+    import { PluginConfig } from "@babel/parser";
+
+==== /packages/compiler-sfc/src/index.ts (0 errors) ====
+    import { createPlugin } from "@babel/parser";
+    export function resolveParserPlugins() {
+      return [createPlugin()];
+    }
+
+==== /node_modules/.pnpm/@[email protected]/node_modules/@babel/parser/package.json (0 errors) ====
+    {
+      "name": "@babel/parser",
+      "version": "7.23.6",
+      "main": "./lib/index.js",
+      "types": "./typings/babel-parser.d.ts"
+    }
+
+==== /node_modules/.pnpm/@[email protected]/node_modules/@babel/parser/typings/babel-parser.d.ts (0 errors) ====
+    export declare function createPlugin(): PluginConfig;
+    export declare class PluginConfig {}
+
+==== /packages/compiler-core/package.json (0 errors) ====
+    {
+      "name": "@vue/compiler-core",
+      "version": "3.0.0",
+      "main": "./src/index.ts",
+      "dependencies": {
+        "@babel/parser": "^7.0.0"
+      }
+    }
+
+==== /packages/compiler-sfc/package.json (0 errors) ====
+    {
+      "name": "@vue/compiler-sfc",
+      "version": "3.0.0",
+      "main": "./src/index.ts",
+      "dependencies": {
+        "@babel/parser": "^7.0.0",
+        "@vue/compiler-core": "^3.0.0"
+      }
+    }
+
diff --git a/tests/baselines/reference/declarationEmitPathMappingMonorepo.errors.txt b/tests/baselines/reference/declarationEmitPathMappingMonorepo.errors.txt
@@ -0,0 +1,34 @@
+packages/b/tsconfig.json(5,9): error TS5101: Option 'baseUrl' is deprecated and will stop functioning in TypeScript 7.0. Specify compilerOption '"ignoreDeprecations": "6.0"' to silence this error.
+  Visit https://aka.ms/ts6 for migration information.
+
+
+==== packages/b/tsconfig.json (1 errors) ====
+    {
+        "compilerOptions": {
+            "outDir": "dist",
+            "declaration": true,
+            "baseUrl": ".",
+            ~~~~~~~~~
+!!! error TS5101: Option 'baseUrl' is deprecated and will stop functioning in TypeScript 7.0. Specify compilerOption '"ignoreDeprecations": "6.0"' to silence this error.
+!!! error TS5101:   Visit https://aka.ms/ts6 for migration information.
+            "paths": {
+                "@ts-bug/a": ["../a"]
+            }
+        }
+    }
+
+
+==== packages/b/src/index.ts (0 errors) ====
+    import { a } from "@ts-bug/a";
+
+    export function b(text: string) {
+      return a(text);
+    }
+==== packages/a/index.d.ts (0 errors) ====
+    declare module "@ts-bug/a" {
+        export type AText = {
+          value: string;
+        };
+        export function a(text: string): AText;
+      }
+
diff --git a/tests/baselines/reference/declarationEmitPathMappingMonorepo2.errors.txt b/tests/baselines/reference/declarationEmitPathMappingMonorepo2.errors.txt
@@ -0,0 +1,51 @@
+packages/lab/tsconfig.json(5,9): error TS5101: Option 'baseUrl' is deprecated and will stop functioning in TypeScript 7.0. Specify compilerOption '"ignoreDeprecations": "6.0"' to silence this error.
+  Visit https://aka.ms/ts6 for migration information.
+
+
+==== packages/lab/tsconfig.json (1 errors) ====
+    {
+        "compilerOptions": {
+            "outDir": "dist",
+            "declaration": true,
+            "baseUrl": "../",
+            ~~~~~~~~~
+!!! error TS5101: Option 'baseUrl' is deprecated and will stop functioning in TypeScript 7.0. Specify compilerOption '"ignoreDeprecations": "6.0"' to silence this error.
+!!! error TS5101:   Visit https://aka.ms/ts6 for migration information.
+            "paths": {
+                "@ts-bug/core": ["./core/src"],
+                "@ts-bug/core/*": ["./core/src/*"],
+                "@ts-bug/lab": ["./lab/src"],
+                "@ts-bug/lab/*": ["./lab/src/*"],
+                "@ts-bug/styles": ["./styles/src"],
+                "@ts-bug/styles/*": ["./styles/src/*"]
+            }
+        }
+    }
+==== packages/lab/src/index.ts (0 errors) ====
+    import { createSvgIcon } from "@ts-bug/core/utils";
+    export default createSvgIcon("Hello", "ArrowLeft");
+
+==== packages/core/src/index.d.ts (0 errors) ====
+    export * from "./utils";
+    export { default as SvgIcon } from "./SvgIcon";
+
+==== packages/core/src/SvgIcon.d.ts (0 errors) ====
+    import { StyledComponentProps } from "@ts-bug/styles";
+    export interface SvgIconProps extends StyledComponentProps<"root"> {
+        children?: string[];
+    }
+    export interface SomeInterface {
+        myProp: string;
+    }
+    declare const SvgIcon: SomeInterface;
+    export default SvgIcon;
+
+==== packages/core/src/utils.d.ts (0 errors) ====
+    import SvgIcon from "./SvgIcon";
+    export function createSvgIcon(path: string, displayName: string): typeof SvgIcon;
+
+==== packages/styles/src/index.d.ts (0 errors) ====
+    export interface StyledComponentProps<ClassKey extends string> {
+        classes?: Record<ClassKey, string>;
+    }
+
diff --git a/tests/baselines/reference/declarationEmitPrefersPathKindBasedOnBundling.errors.txt b/tests/baselines/reference/declarationEmitPrefersPathKindBasedOnBundling.errors.txt
@@ -0,0 +1,24 @@
+error TS5101: Option 'baseUrl' is deprecated and will stop functioning in TypeScript 7.0. Specify compilerOption '"ignoreDeprecations": "6.0"' to silence this error.
+  Visit https://aka.ms/ts6 for migration information.
+
+
+!!! error TS5101: Option 'baseUrl' is deprecated and will stop functioning in TypeScript 7.0. Specify compilerOption '"ignoreDeprecations": "6.0"' to silence this error.
+!!! error TS5101:   Visit https://aka.ms/ts6 for migration information.
+==== src/lib/operators/scalar.ts (0 errors) ====
+    export interface Scalar {
+    	(): string;
+    	value: number;
+    }
+
+    export function scalar(value: string): Scalar {
+    	return null as any;
+    }
+==== src/settings/spacing.ts (0 errors) ====
+    import { scalar } from '../lib/operators/scalar';
+
+    export default {
+    	get xs() {
+    		return scalar("14px");
+    	}
+    };
+
diff --git a/tests/baselines/reference/declarationEmitPrefersPathKindBasedOnBundling.types b/tests/baselines/reference/declarationEmitPrefersPathKindBasedOnBundling.types
@@ -16,6 +16,7 @@ export function scalar(value: string): Scalar {
 
 	return null as any;
 >null as any : any
+>            : ^^^
 }
 === src/settings/spacing.ts ===
 import { scalar } from '../lib/operators/scalar';

diff --git a/tests/baselines/reference/declarationEmitPrefersPathKindBasedOnBundling2.errors.txt b/tests/baselines/reference/declarationEmitPrefersPathKindBasedOnBundling2.errors.txt
@@ -0,0 +1,24 @@
+error TS5101: Option 'baseUrl' is deprecated and will stop functioning in TypeScript 7.0. Specify compilerOption '"ignoreDeprecations": "6.0"' to silence this error.
+  Visit https://aka.ms/ts6 for migration information.
+
+
+!!! error TS5101: Option 'baseUrl' is deprecated and will stop functioning in TypeScript 7.0. Specify compilerOption '"ignoreDeprecations": "6.0"' to silence this error.
+!!! error TS5101:   Visit https://aka.ms/ts6 for migration information.
+==== src/lib/operators/scalar.ts (0 errors) ====
+    export interface Scalar {
+    	(): string;
+    	value: number;
+    }
+
+    export function scalar(value: string): Scalar {
+    	return null as any;
+    }
+==== src/settings/spacing.ts (0 errors) ====
+    import { scalar } from '../lib/operators/scalar';
+
+    export default {
+    	get xs() {
+    		return scalar("14px");
+    	}
+    };
+
diff --git a/tests/baselines/reference/declarationEmitPrefersPathKindBasedOnBundling2.types b/tests/baselines/reference/declarationEmitPrefersPathKindBasedOnBundling2.types
@@ -16,6 +16,7 @@ export function scalar(value: string): Scalar {
 
 	return null as any;
 >null as any : any
+>            : ^^^
 }
 === src/settings/spacing.ts ===
 import { scalar } from '../lib/operators/scalar';