From ad2ee714c29d662665ee0ed1859fbeb918a12b18 Mon Sep 17 00:00:00 2001
From: whitequark <whitequark@whitequark.org>
Date: Fri, 9 Jun 2017 07:29:08 +0000
Subject: [PATCH] compiler: do not permit iterating str values.

This currently breaks badly on UTF-8, and doesn't even return
a value of a correct type.
---
 artiq/compiler/transforms/inferencer.py     | 2 +-
 artiq/test/lit/inferencer/error_str_iter.py | 5 +++++
 2 files changed, 6 insertions(+), 1 deletion(-)
 create mode 100644 artiq/test/lit/inferencer/error_str_iter.py

diff --git a/artiq/compiler/transforms/inferencer.py b/artiq/compiler/transforms/inferencer.py
index 0003f214e..c4fb07b94 100644
--- a/artiq/compiler/transforms/inferencer.py
+++ b/artiq/compiler/transforms/inferencer.py
@@ -183,7 +183,7 @@ class Inferencer(algorithm.Visitor):
         if builtins.is_bytes(collection.type) or builtins.is_bytearray(collection.type):
             self._unify(element.type, builtins.get_iterable_elt(collection.type),
                         element.loc, None)
-        elif builtins.is_iterable(collection.type):
+        elif builtins.is_iterable(collection.type) and not builtins.is_str(collection.type):
             rhs_type = collection.type.find()
             rhs_wrapped_lhs_type = types.TMono(rhs_type.name, {"elt": element.type})
             self._unify(rhs_wrapped_lhs_type, rhs_type,
diff --git a/artiq/test/lit/inferencer/error_str_iter.py b/artiq/test/lit/inferencer/error_str_iter.py
new file mode 100644
index 000000000..a79c52f83
--- /dev/null
+++ b/artiq/test/lit/inferencer/error_str_iter.py
@@ -0,0 +1,5 @@
+# RUN: %python -m artiq.compiler.testbench.inferencer +diag %s >%t
+# RUN: OutputCheck %s --file-to-check=%t
+
+# CHECK-L: ${LINE:+1}: error: type str is not iterable
+("a")[0]