Extended the defineConstant mechanism to work with conditional statements that contain member access expressions that reference a defined member name. This addresses https://github.com/microsoft/pyright/issues/4060.

docs/configuration.md

@@ -16,7 +16,7 @@ Relative paths specified within the config file are relative to the config file
 
 **strict** [array of paths, optional]: Paths of directories or files that should use “strict” analysis if they are included. This is the same as manually adding a “# pyright: strict” comment. In strict mode, most type-checking rules are enabled. Refer to [this table](https://github.com/microsoft/pyright/blob/main/docs/configuration.md#diagnostic-rule-defaults) for details about which rules are enabled in strict mode. Paths may contain wildcard characters ** (a directory or multiple levels of directories), * (a sequence of zero or more characters), or ? (a single character).
 
-**defineConstant** [map of constants to values (boolean or string), optional]: Set of identifiers that should be assumed to contain a constant value wherever used within this program. For example, `{ "DEBUG": true }` indicates that pyright should assume that the identifier `DEBUG` will always be equal to `True`. If this identifier is used within a conditional expression (such as `if not DEBUG:`) pyright will use the indicated value to determine whether the guarded block is reachable or not.
+**defineConstant** [map of constants to values (boolean or string), optional]: Set of identifiers that should be assumed to contain a constant value wherever used within this program. For example, `{ "DEBUG": true }` indicates that pyright should assume that the identifier `DEBUG` will always be equal to `True`. If this identifier is used within a conditional expression (such as `if not DEBUG:`) pyright will use the indicated value to determine whether the guarded block is reachable or not. Member expressions that reference one of these constants (e.g. `my_module.DEBUG`) are also supported.
 
 **typeshedPath** [path, optional]: Path to a directory that contains typeshed type stub files. Pyright ships with a bundled copy of typeshed type stubs. If you want to use a different version of typeshed stubs, you can clone the [typeshed github repo](https://github.com/python/typeshed) to a local directory and reference the location with this path. This option is useful if you’re actively contributing updates to typeshed.
 

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

@@ -118,11 +118,15 @@ export function evaluateStaticBoolExpression(
             }
         } else {
             // Handle the special case of <definedConstant> == 'X' or <definedConstant> != 'X'.
-            if (
-                node.leftExpression.nodeType === ParseNodeType.Name &&
-                node.rightExpression.nodeType === ParseNodeType.StringList
-            ) {
-                const constantValue = definedConstants.get(node.leftExpression.value);
+            if (node.rightExpression.nodeType === ParseNodeType.StringList) {
+                let constantValue: string | number | boolean | undefined;
+
+                if (node.leftExpression.nodeType === ParseNodeType.Name) {
+                    constantValue = definedConstants.get(node.leftExpression.value);
+                } else if (node.leftExpression.nodeType === ParseNodeType.MemberAccess) {
+                    constantValue = definedConstants.get(node.leftExpression.memberName.value);
+                }
+
                 if (constantValue !== undefined && typeof constantValue === 'string') {
                     const comparisonStringName = node.rightExpression.strings.map((s) => s.value).join('');
                     return _evaluateStringBinaryOperation(node.operator, constantValue, comparisonStringName);
@@ -144,14 +148,20 @@ export function evaluateStaticBoolExpression(
         if (constant !== undefined) {
             return !!constant;
         }
-    } else if (
-        typingImportAliases &&
-        node.nodeType === ParseNodeType.MemberAccess &&
-        node.memberName.value === 'TYPE_CHECKING' &&
-        node.leftExpression.nodeType === ParseNodeType.Name &&
-        typingImportAliases.some((alias) => alias === (node.leftExpression as NameNode).value)
-    ) {
-        return true;
+    } else if (node.nodeType === ParseNodeType.MemberAccess) {
+        if (
+            typingImportAliases &&
+            node.memberName.value === 'TYPE_CHECKING' &&
+            node.leftExpression.nodeType === ParseNodeType.Name &&
+            typingImportAliases.some((alias) => alias === (node.leftExpression as NameNode).value)
+        ) {
+            return true;
+        }
+
+        const constant = definedConstants.get(node.memberName.value);
+        if (constant !== undefined) {
+            return !!constant;
+        }
     }
 
     return undefined;

packages/pyright-internal/src/tests/samples/staticExpressions1.py

@@ -50,3 +50,25 @@ if DEFINED_STR == "hi!":
     x = 1
 else:
     x = "error!"
+
+class Dummy:
+    DEFINED_FALSE: bool
+    DEFINED_TRUE: bool
+    DEFINED_STR: str
+
+dummy = Dummy()
+
+if dummy.DEFINED_TRUE:
+    x = 1
+else:
+    x = "error!"
+
+if not dummy.DEFINED_FALSE:
+    x = 1
+else:
+    x = "error!"
+
+if dummy.DEFINED_STR == "hi!":
+    x = 1
+else:
+    x = "error!"

packages/pyright-internal/src/tests/typeEvaluator1.test.ts

@@ -1374,13 +1374,13 @@ test('StaticExpressions1', () => {
     configOptions.defaultPythonPlatform = 'windows';
 
     const analysisResults1 = TestUtils.typeAnalyzeSampleFiles(['staticExpressions1.py'], configOptions);
-    TestUtils.validateResults(analysisResults1, 6);
+    TestUtils.validateResults(analysisResults1, 9);
 
     configOptions.defaultPythonVersion = PythonVersion.V3_11;
     configOptions.defaultPythonPlatform = 'Linux';
 
     const analysisResults2 = TestUtils.typeAnalyzeSampleFiles(['staticExpressions1.py'], configOptions);
-    TestUtils.validateResults(analysisResults2, 3);
+    TestUtils.validateResults(analysisResults2, 6);
 
     configOptions.defineConstant.set('DEFINED_TRUE', true);
     configOptions.defineConstant.set('DEFINED_FALSE', false);