From f1a3dc1e235e2df7deb89c9166f5751e08b418c7 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=C3=89loi=20Rivard?= <eloi@yaal.coop>
Date: Fri, 29 Dec 2023 20:31:43 +0100
Subject: [PATCH] fix: :class:`~fields.SelectMultipleField` value coercion on
 validation.

Co-authored-by: Andy Caine <acaine00@gmail.com>
---
 CHANGES.rst                         |  6 ++++++
 src/wtforms/fields/choices.py       | 15 +++++++++------
 tests/fields/test_selectmultiple.py | 13 +++++++++++++
 3 files changed, 28 insertions(+), 6 deletions(-)

diff --git a/CHANGES.rst b/CHANGES.rst
index 186501bcb..18129d459 100644
--- a/CHANGES.rst
+++ b/CHANGES.rst
@@ -1,5 +1,11 @@
 .. currentmodule:: wtforms
 
+Unreleased
+----------
+
+- Fix :class:`~fields.SelectMultipleField` value coercion on validation.
+  :issue:`822` :pr:`823`
+
 Version 3.1.1
 -------------
 
diff --git a/src/wtforms/fields/choices.py b/src/wtforms/fields/choices.py
index 2b1fd2e08..62ed49763 100644
--- a/src/wtforms/fields/choices.py
+++ b/src/wtforms/fields/choices.py
@@ -121,8 +121,9 @@ def _choices_generator(self, choices):
             _choices = zip(choices, choices)
 
         for value, label, *other_args in _choices:
+            selected = self.coerce(value) == self.data
             render_kw = other_args[0] if len(other_args) else {}
-            yield (value, label, self.coerce(value) == self.data, render_kw)
+            yield (value, label, selected, render_kw)
 
     def process_data(self, value):
         try:
@@ -173,9 +174,9 @@ def _choices_generator(self, choices):
         else:
             _choices = zip(choices, choices)
 
-        for value, label, *args in _choices:
+        for value, label, *other_args in _choices:
             selected = self.data is not None and self.coerce(value) in self.data
-            render_kw = args[0] if len(args) else {}
+            render_kw = other_args[0] if len(other_args) else {}
             yield (value, label, selected, render_kw)
 
     def process_data(self, value):
@@ -201,9 +202,11 @@ def pre_validate(self, form):
         if self.choices is None:
             raise TypeError(self.gettext("Choices cannot be None."))
 
-        acceptable = {c[0] for c in self.iter_choices()}
-        if any(d not in acceptable for d in self.data):
-            unacceptable = [str(d) for d in set(self.data) - acceptable]
+        acceptable = [self.coerce(choice[0]) for choice in self.iter_choices()]
+        if any(data not in acceptable for data in self.data):
+            unacceptable = [
+                str(data) for data in set(self.data) if data not in acceptable
+            ]
             raise ValidationError(
                 self.ngettext(
                     "'%(value)s' is not a valid choice for this field.",
diff --git a/tests/fields/test_selectmultiple.py b/tests/fields/test_selectmultiple.py
index 5fd2a99b7..127fe45ab 100644
--- a/tests/fields/test_selectmultiple.py
+++ b/tests/fields/test_selectmultiple.py
@@ -190,3 +190,16 @@ def test_optgroup_option_render_kw():
     assert list(form.a.iter_choices()) == [
         ("a", "Foo", True, {"title": "foobar", "data-foo": "bar"})
     ]
+
+
+def test_can_supply_coercable_values_as_options():
+    F = make_form(
+        a=SelectMultipleField(
+            choices=[("1", "One"), ("2", "Two")],
+            coerce=int,
+        )
+    )
+    post_data = DummyPostData(a=["1", "2"])
+    form = F(post_data)
+    assert form.validate()
+    assert form.a.data == [1, 2]