Run statements in the second argument of assert

I've edited the test to use a list instead of a set because the order of evaluation probably ought to be guaranteed.

NEWS.rst

@@ -9,6 +9,10 @@ Removals
 * Support for attribute lists in `defclass` has been removed. Use `setv`
   and `defn` instead.
 
+Bug Fixes
+------------------------------
+* Statements in the second argument of `assert` are now executed.
+
 0.17.0
 ==============================
 

hy/compiler.py

@@ -820,11 +820,22 @@ class HyASTCompiler(object):
 
     @special("assert", [FORM, maybe(FORM)])
     def compile_assert_expression(self, expr, root, test, msg):
+        if msg is None or type(msg) is HySymbol:
             ret = self.compile(test)
-        e = ret.force_expr
-        if msg is not None:
-            msg = self.compile(msg).force_expr
-        return ret + asty.Assert(expr, test=e, msg=msg)
+            return ret + asty.Assert(
+                expr,
+                test=ret.force_expr,
+                msg=(None if msg is None else self.compile(msg).force_expr))
+
+        # The `msg` part may involve statements, which we only
+        # want to be executed if the assertion fails. Rewrite the
+        # form to set `msg` to a variable.
+        msg_var = self.get_anon_var()
+        return self.compile(mkexpr(
+            'if*', mkexpr('and', '__debug__', mkexpr('not', [test])),
+                mkexpr('do',
+                    mkexpr('setv', msg_var, [msg]),
+                    mkexpr('assert', 'False', msg_var))).replace(expr))
 
     @special(["global", "nonlocal"], [oneplus(SYM)])
     def compile_global_or_nonlocal(self, expr, root, syms):

tests/native_tests/language.hy

@@ -1653,16 +1653,15 @@ macros()
    (= (identify-keywords 1 "bloo" :foo)
       ["other" "other" "keyword"])))
 
-#@(pytest.mark.xfail
 (defn test-assert-multistatements []
   ; https://github.com/hylang/hy/issues/1390
-  (setv s (set))
+  (setv l [])
   (defn f [x]
-    (.add s x)
+    (.append l x)
     False)
   (with [(pytest.raises AssertionError)]
     (assert (do (f 1) (f 2)) (do (f 3) (f 4))))
-  (assert (= s #{1 2 3 4}))))
+  (assert (= l [1 2 3 4])))
 
 (defn test-underscore_variables []
   ; https://github.com/hylang/hy/issues/1340