Added support for PEP 675 (arbitrary literal strings)

Author: msfterictraut

README.md

@@ -29,7 +29,9 @@ Pyright supports [configuration files](/docs/configuration.md) that provide gran
 * [PEP 647](https://www.python.org/dev/peps/pep-0647/) user-defined type guards
 * [PEP 655](https://www.python.org/dev/peps/pep-0655/) required typed dictionary items
 * [PEP 673](https://www.python.org/dev/peps/pep-0673/) Self type
+* [PEP 675](https://www.python.org/dev/peps/pep-0675/) arbitrary literal strings
 * [PEP 677](https://www.python.org/dev/peps/pep-0677/) callable type syntax
+* [PEP 681](https://www.python.org/dev/peps/pep-0681/) dataclass transform
 * Type inference for function return values, instance variables, class variables, and globals
 * Type guards that understand conditional code flow constructs like if/else statements
 

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

@@ -3842,6 +3842,7 @@ export class Binder extends ParseTreeWalker {
             ['Self', true],
             ['NoReturn', true],
             ['Never', true],
+            ['LiteralString', true],
         ]);
 
         const assignedName = assignedNameNode.value;

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

@@ -13610,6 +13610,7 @@ export function createTypeEvaluator(importLookup: ImportLookup, evaluatorOptions
             ['Self', { alias: '', module: 'builtins' }],
             ['NoReturn', { alias: '', module: 'builtins' }],
             ['Never', { alias: '', module: 'builtins' }],
+            ['LiteralString', { alias: '', module: 'builtins' }],
         ]);
 
         const aliasMapEntry = specialTypes.get(assignedName);
@@ -16956,6 +16957,10 @@ export function createTypeEvaluator(importLookup: ImportLookup, evaluatorOptions
                 case 'Self': {
                     return createSelfType(classType, errorNode, typeArgs);
                 }
+
+                case 'LiteralString': {
+                    return createSpecialType(classType, typeArgs, 0);
+                }
             }
         }
 
@@ -20750,6 +20755,12 @@ export function createTypeEvaluator(importLookup: ImportLookup, evaluatorOptions
                     }
                 }
 
+                if (ClassType.isBuiltIn(destType, 'LiteralString') && ClassType.isBuiltIn(concreteSrcType, 'str')) {
+                    if (concreteSrcType.literalValue !== undefined) {
+                        return true;
+                    }
+                }
+
                 if (
                     !canAssignClass(
                         ClassType.cloneAsInstantiable(destType),

packages/pyright-internal/src/tests/samples/literalString1.py

@@ -0,0 +1,25 @@
+# This sample tests the evaluation of LiteralString as described
+# in PEP 675.
+
+from typing_extensions import LiteralString
+
+
+def func1(a: str, b: bytes):
+    # This should generate an error.
+    v1: LiteralString = a
+
+    # This should generate an error.
+    v2: LiteralString = b
+
+    # This should generate an error.
+    v3: LiteralString = b""
+
+    v4: LiteralString = "Hello!"
+
+    v5: LiteralString = "Hello " + "Bob"
+
+    # This should generate an error.
+    v6: LiteralString = f"{a}"
+
+    # This should generate an error.
+    v7: LiteralString[int]

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

@@ -1246,3 +1246,9 @@ test('PseudoGeneric1', () => {
 
     TestUtils.validateResults(analysisResults, 0);
 });
+
+test('LiteralString1', () => {
+    const analysisResults = TestUtils.typeAnalyzeSampleFiles(['literalString1.py']);
+
+    TestUtils.validateResults(analysisResults, 5);
+});

packages/pyright-internal/typeshed-fallback/stdlib/typing_extensions.pyi

@@ -145,9 +145,12 @@ else:
     def assert_never(__arg: NoReturn) -> NoReturn: ...
 
 # Experimental (hopefully these will be in 3.11)
+
+# PEP 655
 Required: _SpecialForm
 NotRequired: _SpecialForm
 
+# PEP 681
 def dataclass_transform(
     *,
     eq_default: bool = ...,
@@ -156,7 +159,7 @@ def dataclass_transform(
     field_descriptors: tuple[type[Any] | Callable[..., Any], ...] = ...,
 ) -> Callable[[_T], _T]: ...
 
-# Experimental types, not yet implemented in typing_extensions library.
+# Types not yet implemented in typing_extensions library
 
 # PEP 646
 Unpack: _SpecialForm = ...
@@ -165,4 +168,8 @@ class TypeVarTuple:
     __name__: str
     def __init__(self, name: str) -> None: ...
 
+# PEP 675
+LiteralString: _SpecialForm = ...
+
+# Proposed extension to PEP 647
 StrictTypeGuard: _SpecialForm = ...