From 6a8bdda2a6f21a59eae75abe3a10866fe7e857f4 Mon Sep 17 00:00:00 2001
From: Dennis Korpel <dennis@sarc.nl>
Date: Tue, 28 Jan 2025 15:57:51 +0100
Subject: [PATCH] Fix #20763 - Inconsistent handling of type + value in typeof
 expressions

---
 compiler/src/dmd/expressionsem.d           | 11 ++++++----
 compiler/test/fail_compilation/test20763.d | 25 ++++++++++++++++++++++
 2 files changed, 32 insertions(+), 4 deletions(-)
 create mode 100644 compiler/test/fail_compilation/test20763.d

diff --git a/compiler/src/dmd/expressionsem.d b/compiler/src/dmd/expressionsem.d
index b7d44dddc93..2c798d3318b 100644
--- a/compiler/src/dmd/expressionsem.d
+++ b/compiler/src/dmd/expressionsem.d
@@ -14771,11 +14771,14 @@ private bool checkArithmetic(Expression e, EXP op)
         return true;
     }
 
-    // FIXME: Existing code relies on adding / subtracting types in typeof() expressions:
-    // alias I = ulong; alias U = typeof(I + 1u);
-    // https://github.com/dlang/dmd/issues/20763
-    if (op == EXP.add || op == EXP.min)
+    if ((op == EXP.add || op == EXP.min) && e.isTypeExp())
+    {
+        // @@@DEPRECATED_2.121@@@
+        // Deprecated in 2.111
+        // In 2.121, remove this branch to let `checkValue` raise the error
+        deprecation(e.loc, "type `%s` has no value", e.toChars);
         return false;
+    }
 
     return e.checkValue();
 }
diff --git a/compiler/test/fail_compilation/test20763.d b/compiler/test/fail_compilation/test20763.d
new file mode 100644
index 00000000000..d663da4f65b
--- /dev/null
+++ b/compiler/test/fail_compilation/test20763.d
@@ -0,0 +1,25 @@
+/*
+REQUIRED_ARGS: -de
+
+TEST_OUTPUT:
+---
+fail_compilation\test20763.d(19): Deprecation: type `ulong` has no value
+fail_compilation\test20763.d(20): Deprecation: type `ulong` has no value
+fail_compilation\test20763.d(21): Error: type `ulong` has no value
+fail_compilation\test20763.d(22): Error: type `ulong` has no value
+fail_compilation\test20763.d(23): Error: type `ulong` has no value
+fail_compilation\test20763.d(24): Error: type `ulong` has no value
+---
+*/
+
+// https://github.com/dlang/dmd/issues/20763
+void test()
+{
+    alias I = ulong;
+    alias U0 = typeof(I + 1u);
+    alias U1 = typeof(1 - I);
+    alias U2 = typeof(+I);
+    alias U3 = typeof(I * 1);
+    alias U4 = typeof(I << 1);
+    alias U5 = typeof(I | 1);
+}