Added new diagnostic rule "reportInvalidTypeVarUse" that controls reporting of TypeVars that appear only once in a function signature. By default it is off in basic type checking mode but on in strict mode.

docs/configuration.md

@@ -112,6 +112,8 @@ The following settings control pyright’s diagnostic output (warnings or errors
 
 **reportMissingTypeArgument** [boolean or string, optional]: Generate or suppress diagnostics when a generic class is used without providing explicit or implicit type arguments. The default value for this setting is 'none'.
 
+**reportInvalidTypeVarUse** [boolean or string, optional]: Generate or suppress diagnostics when a TypeVar is used inappropriately (e.g. if a TypeVar appears only once) within a generic function signature. The default value for this setting is 'none'.
+
 **reportCallInDefaultInitializer** [boolean or string, optional]: Generate or suppress diagnostics for function calls within a default value initialization expression. Such calls can mask expensive operations that are performed at module initialization time. The default value for this setting is 'none'.
 
 **reportUnnecessaryIsInstance** [boolean or string, optional]: Generate or suppress diagnostics for 'isinstance' or 'issubclass' calls where the result is statically determined to be always true or always false. Such calls are often indicative of a programming error. The default value for this setting is 'none'.

packages/pyright-internal/src/analyzer/checker.ts

@@ -796,6 +796,11 @@ export class Checker extends ParseTreeWalker {
 
     // Verifies that each local type variable is used more than once.
     private _validateFunctionTypeVarUsage(node: FunctionNode) {
+        // Skip this check entirely if it's disabled.
+        if (this._fileInfo.diagnosticRuleSet.reportInvalidTypeVarUse === 'none') {
+            return;
+        }
+
         const localTypeVarUsage = new Map<string, NameNode[]>();
 
         const nameWalker = new ParseTreeUtils.NameNodeWalker((nameNode) => {
@@ -827,8 +832,8 @@ export class Checker extends ParseTreeWalker {
         localTypeVarUsage.forEach((nameNodes) => {
             if (nameNodes.length === 1) {
                 this._evaluator.addDiagnostic(
-                    this._fileInfo.diagnosticRuleSet.reportGeneralTypeIssues,
-                    DiagnosticRule.reportGeneralTypeIssues,
+                    this._fileInfo.diagnosticRuleSet.reportInvalidTypeVarUse,
+                    DiagnosticRule.reportInvalidTypeVarUse,
                     Localizer.Diagnostic.typeVarUsedOnlyOnce().format({
                         name: nameNodes[0].value,
                     }),

packages/pyright-internal/src/common/configOptions.ts

@@ -192,6 +192,9 @@ export interface DiagnosticRuleSet {
     // Report usage of generic class without explicit type arguments?
     reportMissingTypeArgument: DiagnosticLevel;
 
+    // Report improper usage of type variables within function signatures?
+    reportInvalidTypeVarUse: DiagnosticLevel;
+
     // Report usage of function call within default value
     // initialization expression?
     reportCallInDefaultInitializer: DiagnosticLevel;
@@ -277,6 +280,7 @@ export function getDiagLevelDiagnosticRules() {
         DiagnosticRule.reportUnknownVariableType,
         DiagnosticRule.reportUnknownMemberType,
         DiagnosticRule.reportMissingTypeArgument,
+        DiagnosticRule.reportInvalidTypeVarUse,
         DiagnosticRule.reportCallInDefaultInitializer,
         DiagnosticRule.reportUnnecessaryIsInstance,
         DiagnosticRule.reportUnnecessaryCast,
@@ -338,6 +342,7 @@ export function getOffDiagnosticRuleSet(): DiagnosticRuleSet {
         reportUnknownVariableType: 'none',
         reportUnknownMemberType: 'none',
         reportMissingTypeArgument: 'none',
+        reportInvalidTypeVarUse: 'none',
         reportCallInDefaultInitializer: 'none',
         reportUnnecessaryIsInstance: 'none',
         reportUnnecessaryCast: 'none',
@@ -395,6 +400,7 @@ export function getBasicDiagnosticRuleSet(): DiagnosticRuleSet {
         reportUnknownVariableType: 'none',
         reportUnknownMemberType: 'none',
         reportMissingTypeArgument: 'none',
+        reportInvalidTypeVarUse: 'none',
         reportCallInDefaultInitializer: 'none',
         reportUnnecessaryIsInstance: 'none',
         reportUnnecessaryCast: 'none',
@@ -452,6 +458,7 @@ export function getStrictDiagnosticRuleSet(): DiagnosticRuleSet {
         reportUnknownVariableType: 'error',
         reportUnknownMemberType: 'error',
         reportMissingTypeArgument: 'error',
+        reportInvalidTypeVarUse: 'error',
         reportCallInDefaultInitializer: 'none',
         reportUnnecessaryIsInstance: 'error',
         reportUnnecessaryCast: 'error',
@@ -1020,6 +1027,13 @@ export class ConfigOptions {
                 defaultSettings.reportMissingTypeArgument
             ),
 
+            // Read the "reportInvalidTypeVarUse" entry.
+            reportInvalidTypeVarUse: this._convertDiagnosticLevel(
+                configObj.reportInvalidTypeVarUse,
+                DiagnosticRule.reportInvalidTypeVarUse,
+                defaultSettings.reportInvalidTypeVarUse
+            ),
+
             // Read the "reportCallInDefaultInitializer" entry.
             reportCallInDefaultInitializer: this._convertDiagnosticLevel(
                 configObj.reportCallInDefaultInitializer,

packages/pyright-internal/src/common/diagnosticRules.ts

@@ -49,6 +49,7 @@ export enum DiagnosticRule {
     reportUnknownVariableType = 'reportUnknownVariableType',
     reportUnknownMemberType = 'reportUnknownMemberType',
     reportMissingTypeArgument = 'reportMissingTypeArgument',
+    reportInvalidTypeVarUse = 'reportInvalidTypeVarUse',
     reportCallInDefaultInitializer = 'reportCallInDefaultInitializer',
     reportUnnecessaryIsInstance = 'reportUnnecessaryIsInstance',
     reportUnnecessaryCast = 'reportUnnecessaryCast',

packages/pyright-internal/src/tests/samples/typeVar5.py

@@ -2,6 +2,8 @@
 # a generic function. A TypeVar must appear at least twice to be
 # considered legitimate.
 
+# pyright: reportInvalidTypeVarUse=true
+
 from typing import Dict, Generic, List, TypeVar
 
 

packages/pyright-internal/src/tests/typeEvaluator2.test.ts

@@ -878,7 +878,7 @@ test('ParamSpec1', () => {
 
     configOptions.defaultPythonVersion = PythonVersion.V3_10;
     const results = TestUtils.typeAnalyzeSampleFiles(['paramSpec1.py'], configOptions);
-    TestUtils.validateResults(results, 8);
+    TestUtils.validateResults(results, 7);
 });
 
 test('ParamSpec2', () => {
@@ -906,7 +906,7 @@ test('ParamSpec4', () => {
 
     configOptions.defaultPythonVersion = PythonVersion.V3_10;
     const results = TestUtils.typeAnalyzeSampleFiles(['paramSpec4.py'], configOptions);
-    TestUtils.validateResults(results, 7);
+    TestUtils.validateResults(results, 5);
 });
 
 test('ClassVar1', () => {

packages/vscode-pyright/package.json

@@ -477,6 +477,17 @@
                                 "error"
                             ]
                         },
+                        "reportInvalidTypeVarUse": {
+                            "type": "string",
+                            "description": "Diagnostics for improper use of type variables in a function signature.",
+                            "default": "none",
+                            "enum": [
+                                "none",
+                                "information",
+                                "warning",
+                                "error"
+                            ]
+                        },
                         "reportCallInDefaultInitializer": {
                             "type": "string",
                             "description": "Diagnostics for function calls within a default value initialization expression. Such calls can mask expensive operations that are performed at module initialization time.",

packages/vscode-pyright/schemas/pyrightconfig.schema.json

@@ -321,6 +321,12 @@
       "title": "Controls reporting generic class reference with missing type arguments",
       "default": "none"
     },
+    "reportInvalidTypeVarUse": {
+      "$id": "#/properties/reportInvalidTypeVarUse",
+      "$ref": "#/definitions/diagnostic",
+      "title": "Controls reporting improper use of type variables within function signatures",
+      "default": "none"
+    },
     "reportCallInDefaultInitializer": {
       "$id": "#/properties/reportCallInDefaultInitializer",
       "$ref": "#/definitions/diagnostic",