Added "reportOptionalContextManager" config switch.

client/schemas/pyrightconfig.schema.json

@@ -109,6 +109,12 @@
       "title": "Controls reporting of attempts to use an Optional type as an iterable value",
       "default": "none"
     },
+    "reportOptionalContextManager": {
+      "$id": "#/properties/reportOptionalContextManager",
+      "$ref": "#/definitions/diagnostic",
+      "title": "Controls reporting of attempts to use an Optional type as a parameter to a with statement",
+      "default": "none"
+    },
     "reportUntypedFunctionDecorator": {
       "$id": "#/properties/reportUntypedFunctionDecorator",
       "$ref": "#/definitions/diagnostic",

docs/configuration.md

@@ -44,6 +44,8 @@ The following settings control pyright's diagnostic output (warnings or errors).
 
 **reportOptionalIterable** [boolean or string, optional]: Generate or suppress diagnostics for an attempt to use an Optional type as an iterable value (e.g. within a `for` statement). The default value for this setting is 'none'.
 
+**reportOptionalContextManager** [boolean or string, optional]: Generate or suppress diagnostics for an attempt to use an Optional type as a context manager (as a parameter to a `with` statement). The default value for this setting is 'none'.
+
 **reportUntypedFunctionDecorator** [boolean or string, optional]: Generate or suppress diagnostics for function decorators that have no type annotations. These obscure the function type, defeating many type analysis features.
 
 **reportUntypedClassDecorator** [boolean or string, optional]: Generate or suppress diagnostics for class decorators that have no type annotations. These obscure the class type, defeating many type analysis features.

server/src/analyzer/typeAnalyzer.ts

@@ -623,7 +623,16 @@ export class TypeAnalyzer extends ParseTreeWalker {
         });
 
         node.withItems.forEach(item => {
-            const exprType = this._getTypeOfExpression(item.expression);
+            let exprType = this._getTypeOfExpression(item.expression);
+
+            if (exprType instanceof UnionType && exprType.getTypes().some(t => t instanceof NoneType)) {
+                this._addDiagnostic(
+                    this._fileInfo.configOptions.reportOptionalContextManager,
+                    `Object of type 'None' cannot be used with 'with'`,
+                    node);
+                exprType = exprType.removeOptional();
+            }
+
             const enterMethodName = node.isAsync ? '__aenter__' : '__enter__';
 
             const scopedType = TypeUtils.doForSubtypes(exprType, subtype => {

server/src/common/configOptions.ts

@@ -100,6 +100,9 @@ export class ConfigOptions {
     // Report attempts to use an Optional type as an iterable?
     reportOptionalIterable: DiagnosticLevel = 'none';
 
+    // Report attempts to use an Optional type in a "with" statement?
+    reportOptionalContextManager: DiagnosticLevel = 'none';
+
     // Report untyped function decorators that obscure the function type?
     reportUntypedFunctionDecorator: DiagnosticLevel = 'none';
 
@@ -245,6 +248,10 @@ export class ConfigOptions {
         this.reportOptionalIterable = this._convertDiagnosticLevel(
             configObj.reportOptionalIterable, 'reportOptionalIterable', 'none');
 
+        // Read the "reportOptionalContextManager" entry.
+        this.reportOptionalContextManager = this._convertDiagnosticLevel(
+            configObj.reportOptionalContextManager, 'reportOptionalContextManager', 'none');
+
         // Read the "reportUntypedFunctionDecorator" entry.
         this.reportUntypedFunctionDecorator = this._convertDiagnosticLevel(
             configObj.reportUntypedFunctionDecorator, 'reportUntypedFunctionDecorator', 'none');

server/src/tests/samples/optional1.py

@@ -7,6 +7,9 @@ class Foo:
     def do_stuff(self):
         pass
 
+    def __enter__(self):
+        return 3
+
 a = None
 if 1:
     a = Foo()
@@ -41,3 +44,12 @@ c[2]
 # this should generate an error.
 for val in c:
     pass
+
+# If "reportOptionalContextManager" is enabled,
+# this should generate an error.
+cm = None
+if 1:
+    cm = Foo()
+with cm as val:
+    pass
+

server/src/tests/typeAnalyzer.test.ts

@@ -199,16 +199,18 @@ test('Optional1', () => {
     configOptions.reportOptionalMemberAccess = 'warning';
     configOptions.reportOptionalCall = 'warning';
     configOptions.reportOptionalIterable = 'warning';
+    configOptions.reportOptionalContextManager = 'warning';
     analysisResults = TestUtils.typeAnalyzeSampleFiles(['optional1.py'], configOptions);
-    validateResults(analysisResults, 0, 4);
+    validateResults(analysisResults, 0, 5);
 
     // Turn on errors.
     configOptions.reportOptionalSubscript = 'error';
     configOptions.reportOptionalMemberAccess = 'error';
     configOptions.reportOptionalCall = 'error';
     configOptions.reportOptionalIterable = 'error';
+    configOptions.reportOptionalContextManager = 'error';
     analysisResults = TestUtils.typeAnalyzeSampleFiles(['optional1.py'], configOptions);
-    validateResults(analysisResults, 4);
+    validateResults(analysisResults, 5);
 });
 
 test('Private1', () => {