From ad2cd9c8007407964098b6f2d133d2741403b91d Mon Sep 17 00:00:00 2001
From: BobTheBuidler <70677534+BobTheBuidler@users.noreply.github.com>
Date: Thu, 25 Sep 2025 23:49:19 -0400
Subject: [PATCH 1/6] [mypyc] feat: extend `get_expr_len` to try
 `constant_fold_expr`

get_expr_len currently support StrExpr, BytesExpr, and string-type Final values

constant_fold_expr already has the code to parse values from all of these, so we can deduplicate code by using it

It's able to parse a few more Expressions than our existing implementation, and allows get_expr_length to automatically benefit from future constant-folding enhancements
---
 mypyc/irbuild/for_helpers.py | 22 ++++++++--------------
 1 file changed, 8 insertions(+), 14 deletions(-)

diff --git a/mypyc/irbuild/for_helpers.py b/mypyc/irbuild/for_helpers.py
index 5edee6cb4df4..267232856e5f 100644
--- a/mypyc/irbuild/for_helpers.py
+++ b/mypyc/irbuild/for_helpers.py
@@ -65,6 +65,7 @@
     short_int_rprimitive,
 )
 from mypyc.irbuild.builder import IRBuilder
+from mypyc.irbuild.constant_fold import constant_fold_expr
 from mypyc.irbuild.prepare import GENERATOR_HELPER_NAME
 from mypyc.irbuild.targets import AssignmentTarget, AssignmentTargetTuple
 from mypyc.primitives.dict_ops import (
@@ -1180,26 +1181,19 @@ def gen_cleanup(self) -> None:
             gen.gen_cleanup()
 
 
-def get_expr_length(expr: Expression) -> int | None:
-    if isinstance(expr, (StrExpr, BytesExpr)):
-        return len(expr.value)
+def get_expr_length(builder: IRBuilder, expr: Expression) -> int | None:
+    folded = constant_fold_expr(builder, expr)
+    if isinstance(folded, (str, bytes)):
+        return len(folded)
     elif isinstance(expr, (ListExpr, TupleExpr)):
         # if there are no star expressions, or we know the length of them,
         # we know the length of the expression
-        stars = [get_expr_length(i) for i in expr.items if isinstance(i, StarExpr)]
+        stars = [get_expr_length(builder, i) for i in expr.items if isinstance(i, StarExpr)]
         if None not in stars:
             other = sum(not isinstance(i, StarExpr) for i in expr.items)
             return other + sum(stars)  # type: ignore [arg-type]
     elif isinstance(expr, StarExpr):
-        return get_expr_length(expr.expr)
-    elif (
-        isinstance(expr, RefExpr)
-        and isinstance(expr.node, Var)
-        and expr.node.is_final
-        and isinstance(expr.node.final_value, str)
-        and expr.node.has_explicit_value
-    ):
-        return len(expr.node.final_value)
+        return get_expr_length(builder, expr.expr)
     # TODO: extend this, passing length of listcomp and genexp should have worthwhile
     # performance boost and can be (sometimes) figured out pretty easily. set and dict
     # comps *can* be done as well but will need special logic to consider the possibility
@@ -1212,7 +1206,7 @@ def get_expr_length_value(
 ) -> Value:
     rtype = builder.node_type(expr)
     assert is_sequence_rprimitive(rtype), rtype
-    length = get_expr_length(expr)
+    length = get_expr_length(builder, expr)
     if length is None:
         # We cannot compute the length at compile time, so we will fetch it.
         return builder.builder.builtin_len(expr_reg, line, use_pyssize_t=use_pyssize_t)

From f4b7b5a3b6f8f992c0e93a673d0c8ee7911c52a4 Mon Sep 17 00:00:00 2001
From: "pre-commit-ci[bot]"
 <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Date: Fri, 26 Sep 2025 03:51:10 +0000
Subject: [PATCH 2/6] [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci
---
 mypyc/irbuild/for_helpers.py | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/mypyc/irbuild/for_helpers.py b/mypyc/irbuild/for_helpers.py
index 267232856e5f..3b7ea50cdfe8 100644
--- a/mypyc/irbuild/for_helpers.py
+++ b/mypyc/irbuild/for_helpers.py
@@ -11,7 +11,6 @@
 
 from mypy.nodes import (
     ARG_POS,
-    BytesExpr,
     CallExpr,
     DictionaryComprehension,
     Expression,
@@ -23,10 +22,8 @@
     RefExpr,
     SetExpr,
     StarExpr,
-    StrExpr,
     TupleExpr,
     TypeAlias,
-    Var,
 )
 from mypyc.ir.ops import (
     ERR_NEVER,

From c7b559ac62c159a16e80ddd8056fad268d6a705c Mon Sep 17 00:00:00 2001
From: BobTheBuidler <70677534+BobTheBuidler@users.noreply.github.com>
Date: Fri, 26 Sep 2025 00:17:45 -0400
Subject: [PATCH 3/6] Update irbuild-tuple.test

---
 mypyc/test-data/irbuild-tuple.test | 42 ++++++++++++++++++++++++++++++
 1 file changed, 42 insertions(+)

diff --git a/mypyc/test-data/irbuild-tuple.test b/mypyc/test-data/irbuild-tuple.test
index 081cc1b174c9..48ea90279433 100644
--- a/mypyc/test-data/irbuild-tuple.test
+++ b/mypyc/test-data/irbuild-tuple.test
@@ -433,6 +433,48 @@ L4:
     a = r1
     return 1
 
+[case testTupleBuiltFromConstantFolding]
+def f2(val: str) -> str:
+    return val + "f2"
+
+def test() -> None:
+    a = tuple(f2(x) for x in "ab" + "c")
+
+[out]
+def f2(val):
+    val, r0, r1 :: str
+L0:
+    r0 = 'f2'
+    r1 = PyUnicode_Concat(val, r0)
+    return r1
+def test():
+    r0 :: str
+    r1 :: tuple
+    r2 :: native_int
+    r3 :: bit
+    r4, x, r5 :: str
+    r6 :: native_int
+    a :: tuple
+L0:
+    r0 = 'abc'
+    r1 = PyTuple_New(3)
+    r2 = 0
+L1:
+    r3 = r2 < 3 :: signed
+    if r3 goto L2 else goto L4 :: bool
+L2:
+    r4 = CPyStr_GetItemUnsafe(r0, r2)
+    x = r4
+    r5 = f2(x)
+    CPySequenceTuple_SetItemUnsafe(r1, r2, r5)
+L3:
+    r6 = r2 + 1
+    r2 = r6
+    goto L1
+L4:
+    a = r1
+    return 1
+
 [case testTupleBuiltFromFinalStr]
 from typing import Final
 

From 93fd89f48aced860c823ffd30fbf6e8eba4e258c Mon Sep 17 00:00:00 2001
From: BobTheBuidler <70677534+BobTheBuidler@users.noreply.github.com>
Date: Fri, 26 Sep 2025 01:48:33 -0400
Subject: [PATCH 4/6] use a final var in the test

---
 mypyc/test-data/irbuild-tuple.test | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/mypyc/test-data/irbuild-tuple.test b/mypyc/test-data/irbuild-tuple.test
index 48ea90279433..c1bd6b4f8f27 100644
--- a/mypyc/test-data/irbuild-tuple.test
+++ b/mypyc/test-data/irbuild-tuple.test
@@ -434,11 +434,15 @@ L4:
     return 1
 
 [case testTupleBuiltFromConstantFolding]
+from typing import Final
+
+c: Final = "c"
+
 def f2(val: str) -> str:
     return val + "f2"
 
 def test() -> None:
-    a = tuple(f2(x) for x in "ab" + "c")
+    a = tuple(f2(x) for x in "ab" + c)
 
 [out]
 def f2(val):

From a75a9c33915f0f249cfe048893eb1b631a0ed9a1 Mon Sep 17 00:00:00 2001
From: BobTheBuidler <70677534+BobTheBuidler@users.noreply.github.com>
Date: Fri, 26 Sep 2025 07:41:06 -0400
Subject: [PATCH 5/6] add comment

---
 mypyc/test-data/irbuild-tuple.test | 1 +
 1 file changed, 1 insertion(+)

diff --git a/mypyc/test-data/irbuild-tuple.test b/mypyc/test-data/irbuild-tuple.test
index c1bd6b4f8f27..b5f5971294e4 100644
--- a/mypyc/test-data/irbuild-tuple.test
+++ b/mypyc/test-data/irbuild-tuple.test
@@ -442,6 +442,7 @@ def f2(val: str) -> str:
     return val + "f2"
 
 def test() -> None:
+    # `"ab" + c` should constant fold to "abc"
     a = tuple(f2(x) for x in "ab" + c)
 
 [out]

From bab3dac5356ae314c0a677ad87e9152d1d993c6d Mon Sep 17 00:00:00 2001
From: BobTheBuidler <70677534+BobTheBuidler@users.noreply.github.com>
Date: Mon, 29 Sep 2025 11:14:20 -0400
Subject: [PATCH 6/6] Update irbuild-tuple.test

---
 mypyc/test-data/irbuild-tuple.test | 1 +
 1 file changed, 1 insertion(+)

diff --git a/mypyc/test-data/irbuild-tuple.test b/mypyc/test-data/irbuild-tuple.test
index 1ec895720fce..b5d7f7d72a4d 100644
--- a/mypyc/test-data/irbuild-tuple.test
+++ b/mypyc/test-data/irbuild-tuple.test
@@ -465,6 +465,7 @@ L0:
     r0 = 'abc'
     r1 = PyTuple_New(3)
     r2 = 0
+    goto L2
 L1:
     r3 = r2 < 3 :: signed
     if r3 goto L2 else goto L4 :: bool