Added missing check for Final variable assigned in a loop. (#8561)

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

@@ -3058,6 +3058,8 @@ export class Checker extends ParseTreeWalker {
 
                     this._reportMultipleFinalDeclarations(name, symbol, scope.type);
 
+                    this._reportFinalInLoop(symbol);
+
                     this._reportMultipleTypeAliasDeclarations(name, symbol);
 
                     this._reportInvalidOverload(name, symbol);
@@ -3208,6 +3210,25 @@ export class Checker extends ParseTreeWalker {
         });
     }
 
+    private _reportFinalInLoop(symbol: Symbol) {
+        if (!this._evaluator.isFinalVariable(symbol)) {
+            return;
+        }
+
+        const decls = symbol.getDeclarations();
+        if (decls.length === 0) {
+            return;
+        }
+
+        if (ParseTreeUtils.isWithinLoop(decls[0].node)) {
+            this._evaluator.addDiagnostic(
+                DiagnosticRule.reportGeneralTypeIssues,
+                LocMessage.finalInLoop(),
+                decls[0].node
+            );
+        }
+    }
+
     private _reportMultipleFinalDeclarations(name: string, symbol: Symbol, scopeType: ScopeType) {
         if (!this._evaluator.isFinalVariable(symbol)) {
             return;

packages/pyright-internal/src/localization/localize.ts

@@ -497,6 +497,7 @@ export namespace Localizer {
         export const finalClassIsAbstract = () =>
             new ParameterizedString<{ type: string }>(getRawString('Diagnostic.finalClassIsAbstract'));
         export const finalContext = () => getRawString('Diagnostic.finalContext');
+        export const finalInLoop = () => getRawString('Diagnostic.finalInLoop');
         export const finalMethodOverride = () =>
             new ParameterizedString<{ name: string; className: string }>(
                 getRawString('Diagnostic.finalMethodOverride')

packages/pyright-internal/src/localization/package.nls.en-us.json

@@ -197,6 +197,7 @@
         "expectedYieldExpr": "Expected expression in yield statement",
         "finalClassIsAbstract": "Class \"{type}\" is marked final and must implement all abstract symbols",
         "finalContext": "\"Final\" is not allowed in this context",
+        "finalInLoop": "A \"Final\" variable cannot be assigned within a loop",
         "finalMethodOverride": "Method \"{name}\" cannot override final method defined in class \"{className}\"",
         "finalNonMethod": "Function \"{name}\" cannot be marked @final because it is not a method",
         "finalReassigned": "\"{name}\" is declared as Final and cannot be reassigned",

packages/pyright-internal/src/tests/samples/final3.py

@@ -246,3 +246,25 @@ reveal_type(v11, expected_text='Literal[b""]')
 
 v12: Final = b"2" and True
 reveal_type(v12, expected_text="Literal[True]")
+
+
+def func4():
+    while 1 < 1:
+        # This should generate an error because it's in a loop.
+        x1: Final = 1
+
+    for i in range(10):
+        if i < 3:
+            # This should generate an error because it's in a loop.
+            x2: Final[int] = 1
+
+
+class ClassF:
+    while 1 < 2:
+        # This should generate an error because it's in a loop.
+        x1: Final = 1
+
+    for i in range(10):
+        if i < 3:
+            # This should generate an error because it's in a loop.
+            x2: Final[int] = 1

packages/pyright-internal/src/tests/typeEvaluator4.test.ts

@@ -33,7 +33,7 @@ test('Final2', () => {
 
 test('Final3', () => {
     const analysisResults = TestUtils.typeAnalyzeSampleFiles(['final3.py']);
-    TestUtils.validateResults(analysisResults, 38);
+    TestUtils.validateResults(analysisResults, 42);
 });
 
 test('Final4', () => {