Add deprecation warning for alwaysStrict: false

Co-authored-by: RyanCavanaugh <6685088+RyanCavanaugh@users.noreply.github.com>

Author: Copilot

src/compiler/program.ts

@@ -4526,6 +4526,9 @@ export function createProgram(_rootNamesOrOptions: readonly string[] | CreatePro
         });
 
         checkDeprecations("6.0", "7.0", createDiagnostic, createDeprecatedDiagnostic => {
+            if (options.alwaysStrict === false) {
+                createDeprecatedDiagnostic("alwaysStrict", "false", /*useInstead*/ undefined, /*related*/ undefined);
+            }
             if (options.moduleResolution === ModuleResolutionKind.Node10) {
                 createDeprecatedDiagnostic("moduleResolution", "node10", /*useInstead*/ undefined, Diagnostics.Visit_https_Colon_Slash_Slashaka_ms_Slashts6_for_migration_information);
             }

tests/baselines/reference/alwaysStrictDeprecation.errors.txt

@@ -0,0 +1,15 @@
+/foo/tsconfig.json(3,25): error TS5107: Option 'alwaysStrict=false' is deprecated and will stop functioning in TypeScript 7.0. Specify compilerOption '"ignoreDeprecations": "6.0"' to silence this error.
+
+
+==== /foo/tsconfig.json (1 errors) ====
+    {
+        "compilerOptions": {
+            "alwaysStrict": false
+                            ~~~~~
+!!! error TS5107: Option 'alwaysStrict=false' is deprecated and will stop functioning in TypeScript 7.0. Specify compilerOption '"ignoreDeprecations": "6.0"' to silence this error.
+        }
+    }
+    
+==== /foo/a.ts (0 errors) ====
+    const a = 1;
+    

tests/baselines/reference/alwaysStrictDeprecation.js

@@ -0,0 +1,8 @@
+//// [tests/cases/compiler/alwaysStrictDeprecation.ts] ////
+
+//// [a.ts]
+const a = 1;
+
+
+//// [a.js]
+var a = 1;

tests/baselines/reference/alwaysStrictDeprecation.symbols

@@ -0,0 +1,6 @@
+//// [tests/cases/compiler/alwaysStrictDeprecation.ts] ////
+
+=== /foo/a.ts ===
+const a = 1;
+>a : Symbol(a, Decl(a.ts, 0, 5))
+

tests/baselines/reference/alwaysStrictDeprecation.types

@@ -0,0 +1,9 @@
+//// [tests/cases/compiler/alwaysStrictDeprecation.ts] ////
+
+=== /foo/a.ts ===
+const a = 1;
+>a : 1
+>  : ^
+>1 : 1
+>  : ^
+

tests/baselines/reference/alwaysStrictDeprecationSilenced.js

@@ -0,0 +1,8 @@
+//// [tests/cases/compiler/alwaysStrictDeprecationSilenced.ts] ////
+
+//// [a.ts]
+const a = 1;
+
+
+//// [a.js]
+var a = 1;

tests/baselines/reference/alwaysStrictDeprecationSilenced.symbols

@@ -0,0 +1,6 @@
+//// [tests/cases/compiler/alwaysStrictDeprecationSilenced.ts] ////
+
+=== /foo/a.ts ===
+const a = 1;
+>a : Symbol(a, Decl(a.ts, 0, 5))
+

tests/baselines/reference/alwaysStrictDeprecationSilenced.types

@@ -0,0 +1,9 @@
+//// [tests/cases/compiler/alwaysStrictDeprecationSilenced.ts] ////
+
+=== /foo/a.ts ===
+const a = 1;
+>a : 1
+>  : ^
+>1 : 1
+>  : ^
+

tests/cases/compiler/alwaysStrictDeprecation.ts

@@ -0,0 +1,10 @@
+// @typeScriptVersion: 6.0
+// @filename: /foo/tsconfig.json
+{
+    "compilerOptions": {
+        "alwaysStrict": false
+    }
+}
+
+// @filename: /foo/a.ts
+const a = 1;

tests/cases/compiler/alwaysStrictDeprecationSilenced.ts

@@ -0,0 +1,11 @@
+// @typeScriptVersion: 6.0
+// @filename: /foo/tsconfig.json
+{
+    "compilerOptions": {
+        "alwaysStrict": false,
+        "ignoreDeprecations": "6.0"
+    }
+}
+
+// @filename: /foo/a.ts
+const a = 1;