From 117b68e6b74221ec85822f721c23c8245e2294fe Mon Sep 17 00:00:00 2001
From: Mark Koch <48097969+mark-koch@users.noreply.github.com>
Date: Fri, 18 Oct 2024 12:04:04 +0100
Subject: [PATCH] fix: Enable len for linear arrays (#576)

Closes #570
---
 guppylang/prelude/builtins.py           |  2 +-
 tests/error/array_errors/linear_len.err |  7 -------
 tests/error/array_errors/linear_len.py  | 17 -----------------
 tests/integration/test_array.py         | 18 ++++++++++++++++++
 4 files changed, 19 insertions(+), 25 deletions(-)
 delete mode 100644 tests/error/array_errors/linear_len.err
 delete mode 100644 tests/error/array_errors/linear_len.py

diff --git a/guppylang/prelude/builtins.py b/guppylang/prelude/builtins.py
index a1e12c5f..baa079df 100644
--- a/guppylang/prelude/builtins.py
+++ b/guppylang/prelude/builtins.py
@@ -553,7 +553,7 @@ def __getitem__(self: array[L, n], idx: int) -> L: ...
     def __setitem__(self: array[L, n], idx: int, value: L @ owned) -> None: ...
 
     @guppy.custom(checker=ArrayLenChecker())
-    def __len__(self: array[T, n]) -> int: ...
+    def __len__(self: array[L, n]) -> int: ...
 
     @guppy.custom(NewArrayCompiler(), NewArrayChecker(), higher_order_value=False)
     def __new__(): ...
diff --git a/tests/error/array_errors/linear_len.err b/tests/error/array_errors/linear_len.err
deleted file mode 100644
index 0a429cf9..00000000
--- a/tests/error/array_errors/linear_len.err
+++ /dev/null
@@ -1,7 +0,0 @@
-Guppy compilation failed. Error in file $FILE:14
-
-12:    @guppy(module)
-13:    def main(qs: array[qubit, 42]) -> int:
-14:        return len(qs)
-                  ^^^^^^^
-GuppyTypeError: Cannot instantiate non-linear type variable `T` in type `forall T, n: nat. array[T, n] -> int` with linear type `qubit`
diff --git a/tests/error/array_errors/linear_len.py b/tests/error/array_errors/linear_len.py
deleted file mode 100644
index 5f7cc069..00000000
--- a/tests/error/array_errors/linear_len.py
+++ /dev/null
@@ -1,17 +0,0 @@
-import guppylang.prelude.quantum as quantum
-from guppylang.decorator import guppy
-from guppylang.module import GuppyModule
-from guppylang.prelude.builtins import array
-from guppylang.prelude.quantum import qubit
-
-
-module = GuppyModule("test")
-module.load_all(quantum)
-
-
-@guppy(module)
-def main(qs: array[qubit, 42]) -> int:
-    return len(qs)
-
-
-module.compile()
\ No newline at end of file
diff --git a/tests/integration/test_array.py b/tests/integration/test_array.py
index a4b557ac..cedbb1c8 100644
--- a/tests/integration/test_array.py
+++ b/tests/integration/test_array.py
@@ -27,6 +27,24 @@ def main(xs: array[float, 42]) -> int:
     assert val.val.v == 42
 
 
+def test_len_linear(validate):
+    module = GuppyModule("test")
+    module.load(qubit)
+
+    @guppy(module)
+    def main(qs: array[qubit, 42]) -> int:
+        return len(qs)
+
+    package = module.compile()
+    validate(package)
+
+    hg = package.module
+    [val] = [data.op for node, data in hg.nodes() if isinstance(data.op, ops.Const)]
+    assert isinstance(val, ops.Const)
+    assert isinstance(val.val, IntVal)
+    assert val.val.v == 42
+
+
 def test_index(validate):
     @compile_guppy
     def main(xs: array[int, 5], i: int) -> int: