From 7fcc7ac4b663d44344af6123ac71c13c7a71dbf6 Mon Sep 17 00:00:00 2001
From: Kodi Arfer <git@arfer.net>
Date: Tue, 27 Feb 2018 16:33:21 -0800
Subject: [PATCH] Make unary comparison ops evaluate their argument

---
 NEWS.rst                        | 6 ++++++
 hy/compiler.py                  | 3 ++-
 tests/native_tests/operators.hy | 9 +++++++++
 3 files changed, 17 insertions(+), 1 deletion(-)

diff --git a/NEWS.rst b/NEWS.rst
index beb22ed..a1b503f 100644
--- a/NEWS.rst
+++ b/NEWS.rst
@@ -3,6 +3,12 @@
 Unreleased
 ==============================
 
+Other Breaking Changes
+------------------------------
+* Non-shadow unary `=`, `is`, `<`, etc. now evaluate their argument
+  instead of ignoring it. This change increases consistency a bit
+  and makes accidental unary uses easier to notice.
+
 Bug Fixes
 ------------------------------
 * Fix `(return)` so it works correctly to exit a Python 2 generator
diff --git a/hy/compiler.py b/hy/compiler.py
index e6a888e..1132b65 100755
--- a/hy/compiler.py
+++ b/hy/compiler.py
@@ -1574,7 +1574,8 @@ class HyASTCompiler(object):
     @checkargs(min=1)
     def compile_compare_op_expression(self, expression):
         if len(expression) == 2:
-            return asty.Name(expression, id="True", ctx=ast.Load())
+            return (self.compile(expression[1]) +
+                asty.Name(expression, id="True", ctx=ast.Load()))
         return self._compile_compare_op_expression(expression)
 
     @builds("!=", "is_not")
diff --git a/tests/native_tests/operators.hy b/tests/native_tests/operators.hy
index 721ee6c..a32d5ab 100644
--- a/tests/native_tests/operators.hy
+++ b/tests/native_tests/operators.hy
@@ -219,7 +219,15 @@
 
 (op-and-shadow-test [= is]
   (forbid (f))
+
   (assert (is (f "hello") True))
+
+  ; Unary comparison operators, despite always returning True,
+  ; should evaluate their argument.
+  (setv p "a")
+  (assert (is (f (do (setv p "b") "hello")) True))
+  (assert (= p "b"))
+
   (defclass C)
   (setv x (get {"is" (C) "=" 0} f-name))
   (setv y (get {"is" (C) "=" 1} f-name))
@@ -229,6 +237,7 @@
   (assert (is (f y x) False))
   (assert (is (f x x x x x) True))
   (assert (is (f x x x y x) False))
+
   (setv n None)
   (assert (is (f n None) True))
   (assert (is (f n "b") False)))