Add --noStrictGenericChecks compiler option

Author: ahejlsberg

src/compiler/checker.ts

@@ -9509,7 +9509,8 @@ namespace ts {
                     // in the context of the target signature before checking the relationship. Ideally we'd do
                     // this regardless of the number of signatures, but the potential costs are prohibitive due
                     // to the quadratic nature of the logic below.
-                    result = signatureRelatedTo(sourceSignatures[0], targetSignatures[0], /*erase*/ relation === comparableRelation, reportErrors);
+                    const eraseGenerics = relation === comparableRelation || compilerOptions.noStrictGenericChecks;
+                    result = signatureRelatedTo(sourceSignatures[0], targetSignatures[0], eraseGenerics, reportErrors);
                 }
                 else {
                     outer: for (const t of targetSignatures) {

src/compiler/commandLineParser.ts

@@ -620,6 +620,12 @@ namespace ts {
             category: Diagnostics.Advanced_Options,
             description: Diagnostics.The_maximum_dependency_depth_to_search_under_node_modules_and_load_JavaScript_files
         },
+        {
+            name: "noStrictGenericChecks",
+            type: "boolean",
+            category: Diagnostics.Advanced_Options,
+            description: Diagnostics.Disable_strict_checking_of_generic_signatures_in_function_types,
+        },
         {
             // A list of plugins to load in the language service
             name: "plugins",

src/compiler/diagnosticMessages.json

@@ -3278,6 +3278,10 @@
         "category": "Message",
         "code": 6184
     },
+    "Disable strict checking of generic signatures in function types.": {
+        "category": "Message",
+        "code": 6185
+    },
     "Variable '{0}' implicitly has an '{1}' type.": {
         "category": "Error",
         "code": 7005

src/compiler/types.ts

@@ -3522,6 +3522,7 @@ namespace ts {
         noImplicitAny?: boolean;  // Always combine with strict property
         noImplicitReturns?: boolean;
         noImplicitThis?: boolean;  // Always combine with strict property
+        noStrictGenericChecks?: boolean;
         noUnusedLocals?: boolean;
         noUnusedParameters?: boolean;
         noImplicitUseStrict?: boolean;