feat: constant fold common builtin call expressions

mypy/constant_fold.py

@@ -5,16 +5,21 @@
 
 from __future__ import annotations
 
-from typing import Final, Union
+from typing import Any, Callable, Final, Union
 
 from mypy.nodes import (
+    ArgKind,
+    CallExpr,
     ComplexExpr,
     Expression,
     FloatExpr,
     IntExpr,
+    ListExpr,
+    MemberExpr,
     NameExpr,
     OpExpr,
     StrExpr,
+    TupleExpr,
     UnaryExpr,
     Var,
 )
@@ -73,6 +78,8 @@ def constant_fold_expr(expr: Expression, cur_mod_id: str) -> ConstantValue | Non
         value = constant_fold_expr(expr.expr, cur_mod_id)
         if value is not None:
             return constant_fold_unary_op(expr.op, value)
+    elif isinstance(expr, CallExpr):
+        return constant_fold_call_expr(expr, cur_mod_id)
     return None
 
 
@@ -185,3 +192,94 @@ def constant_fold_unary_op(op: str, value: ConstantValue) -> int | float | None:
     elif op == "+" and isinstance(value, (int, float)):
         return value
     return None
+
+
+foldable_builtins: dict[str, Callable[..., Any]] = {
+    "builtins.str": str,
+    "builtins.int": int,
+    "builtins.bool": bool,
+    "builtins.float": float,
+    "builtins.complex": complex,
+    "builtins.repr": repr,
+    "builtins.len": len,
+    "builtins.hasattr": hasattr,
+    "builtins.hex": hex,
+    "builtins.hash": hash,
+    "builtins.min": min,
+    "builtins.max": max,
+    "builtins.oct": oct,
+    "builtins.pow": pow,
+    "builtins.round": round,
+    "builtins.abs": abs,
+    "builtins.ascii": ascii,
+    "builtins.bin": bin,
+    "builtins.chr": chr,
+}
+
+
+def constant_fold_call_expr(
+    expr: CallExpr,
+    cur_mod_id: str,
+    foldable_builtins: dict[str, Callable[..., Any]] = foldable_builtins,
+) -> ConstantValue | None:
+    folded_args: list[ConstantValue]
+
+    callee = expr.callee
+    if isinstance(callee, NameExpr):
+        func = foldable_builtins.get(callee.fullname)
+        if func is None:
+            return None
+
+        folded_args = []
+        for arg in expr.args:
+            val = constant_fold_expr(arg, cur_mod_id)
+            if val is None:
+                return None
+            folded_args.append(val)
+
+        call_args: list[ConstantValue] = []
+        call_kwargs: dict[str, ConstantValue] = {}
+        for folded_arg, arg_kind, arg_name in zip(folded_args, expr.arg_kinds, expr.arg_names):
+            try:
+                if arg_kind == ArgKind.ARG_POS:
+                    call_args.append(folded_arg)
+                elif arg_kind == ArgKind.ARG_NAMED:
+                    call_kwargs[arg_name] = folded_arg  # type: ignore [index]
+                elif arg_kind == ArgKind.ARG_STAR:
+                    call_args.extend(folded_arg)  # type: ignore [arg-type]
+                elif arg_kind == ArgKind.ARG_STAR2:
+                    call_kwargs.update(folded_arg)  # type: ignore [arg-type, call-overload]
+            except:
+                return None
+
+        try:
+            return func(*call_args, **call_kwargs)  # type: ignore [no-any-return]
+        except:
+            return None
+    # --- f-string requires partial support for both str.join and str.format ---
+    elif isinstance(callee, MemberExpr) and isinstance(
+        folded_callee := constant_fold_expr(callee.expr, cur_mod_id), str
+    ):
+        # --- partial str.join constant folding ---
+        if (
+            callee.name == "join"
+            and len(args := expr.args) == 1
+            and isinstance(arg := args[0], (ListExpr, TupleExpr))
+        ):
+            folded_strings: list[str] = []
+            for item in arg.items:
+                val = constant_fold_expr(item, cur_mod_id)
+                if not isinstance(val, str):
+                    return None
+                folded_strings.append(val)
+            return folded_callee.join(folded_strings)
+        # --- str.format constant folding ---
+        elif callee.name == "format":
+            folded_args = []
+            for arg in expr.args:
+                arg_val = constant_fold_expr(arg, cur_mod_id)
+                if arg_val is None:
+                    return None
+                folded_args.append(arg_val)
+            return folded_callee.format(*folded_args)
+    return None

mypyc/test-data/exceptions-freq.test

@@ -99,11 +99,22 @@ hot blocks: [0, 1]
 [case testRareBranch_freq]
 from typing import Final
 
-x: Final = str()
+def setter() -> str:
+    # we need this helper to ensure `x` cannot be constant folded
+    return ""
+
+x: Final = setter()
 
 def f() -> str:
     return x
 [out]
+def setter():
+    r0 :: str
+L0:
+    r0 = ''
+    inc_ref r0
+    return r0
+hot blocks: [0]
 def f():
     r0 :: str
     r1 :: bool
@@ -113,7 +124,7 @@ L0:
     if is_error(r0) goto L1 else goto L3
 L1:
     r1 = raise NameError('value for final name "x" was not set')
-    if not r1 goto L4 (error at f:6) else goto L2 :: bool
+    if not r1 goto L4 (error at f:10) else goto L2 :: bool
 L2:
     unreachable
 L3:

mypyc/test-data/irbuild-basic.test

@@ -3093,18 +3093,8 @@ def f() -> int:
     return x - 1
 [out]
 def f():
-    r0 :: int
-    r1 :: bool
-    r2 :: int
 L0:
-    r0 = __main__.x :: static
-    if is_error(r0) goto L1 else goto L2
-L1:
-    r1 = raise NameError('value for final name "x" was not set')
-    unreachable
-L2:
-    r2 = CPyTagged_Subtract(r0, 2)
-    return r2
+    return 0
 
 [case testFinalRestrictedTypeVar]
 from typing import TypeVar

test-data/unit/check-final.test

@@ -11,7 +11,7 @@ y: Final[float] = int()
 z: Final[int] = int()
 bad: Final[str] = int()  # E: Incompatible types in assignment (expression has type "int", variable has type "str")
 
-reveal_type(x)  # N: Revealed type is "builtins.int"
+reveal_type(x)  # N: Revealed type is "Literal[0]?"
 reveal_type(y)  # N: Revealed type is "builtins.float"
 reveal_type(z)  # N: Revealed type is "builtins.int"
 [out]
@@ -26,10 +26,10 @@ class C:
     bad: Final[str] = int()  # E: Incompatible types in assignment (expression has type "int", variable has type "str")
 class D(C): pass
 
-reveal_type(D.x)  # N: Revealed type is "builtins.int"
+reveal_type(D.x)  # N: Revealed type is "Literal[0]?"
 reveal_type(D.y)  # N: Revealed type is "builtins.float"
 reveal_type(D.z)  # N: Revealed type is "builtins.int"
-reveal_type(D().x)  # N: Revealed type is "builtins.int"
+reveal_type(D().x)  # N: Revealed type is "Literal[0]?"
 reveal_type(D().y)  # N: Revealed type is "builtins.float"
 reveal_type(D().z)  # N: Revealed type is "builtins.int"
 [out]

test-data/unit/check-inference.test

@@ -2174,8 +2174,8 @@ class A:
 [out]
 
 [case testMultipassAndTopLevelVariable]
-y = x # E: Cannot determine type of "x"  # E: Name "x" is used before definition
-y()
+y = x # E: Name "x" is used before definition
+y() # E: "int" not callable
 x = 1+int()
 [out]