From 28bc5c6e7436b6b30b3bac1c31b406bd274f4575 Mon Sep 17 00:00:00 2001
From: Dennis <dkorpel@users.noreply.github.com>
Date: Wed, 29 Jan 2025 11:26:01 +0100
Subject: [PATCH] Fix #20763 - Inconsistent handling of type + value in typeof
 expressions (#20798)

* Fix #20763 - Inconsistent handling of type + value in typeof expressions

* Add supplemental error

---------

Co-authored-by: Dennis Korpel <dennis@sarc.nl>
---
 compiler/src/dmd/expressionsem.d           | 15 ++++++++---
 compiler/src/dmd/typesem.d                 | 12 +++++++++
 compiler/test/fail_compilation/b17285.d    |  7 ++---
 compiler/test/fail_compilation/ice9545.d   |  3 ++-
 compiler/test/fail_compilation/test20763.d | 31 ++++++++++++++++++++++
 5 files changed, 60 insertions(+), 8 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 394bb2d9f423..3b9743e2927d 100644
--- a/compiler/src/dmd/expressionsem.d
+++ b/compiler/src/dmd/expressionsem.d
@@ -14769,11 +14769,16 @@ 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);
+        if (!e.type.isOpaqueType)
+            deprecationSupplemental(e.loc, "perhaps use `%s.init`", e.toChars);
         return false;
+    }
 
     return e.checkValue();
 }
@@ -14844,6 +14849,8 @@ bool checkValue(Expression e)
     if (auto te = e.isTypeExp())
     {
         error(e.loc, "type `%s` has no value", e.toChars());
+        if (!e.type.isOpaqueType)
+            errorSupplemental(e.loc, "perhaps use `%s.init`", e.toChars());
         return true;
     }
 
diff --git a/compiler/src/dmd/typesem.d b/compiler/src/dmd/typesem.d
index 073f0906494b..6d21d67befc5 100644
--- a/compiler/src/dmd/typesem.d
+++ b/compiler/src/dmd/typesem.d
@@ -7609,6 +7609,18 @@ bool checkRetType(TypeFunction tf, const ref Loc loc)
     return false;
 }
 
+/// Returns: whether `t` is a struct/class/enum without a body
+bool isOpaqueType(Type t)
+{
+    if (auto te = t.isTypeEnum())
+        return te.sym.members is null;
+    if (auto ts = t.isTypeStruct())
+        return ts.sym.members is null;
+    if (auto tc = t.isTypeClass())
+        return tc.sym.members is null;
+    return false;
+}
+
 
 /******************************* Private *****************************************/
 
diff --git a/compiler/test/fail_compilation/b17285.d b/compiler/test/fail_compilation/b17285.d
index 7b79cf0666fc..9bf5d96cb247 100644
--- a/compiler/test/fail_compilation/b17285.d
+++ b/compiler/test/fail_compilation/b17285.d
@@ -1,9 +1,10 @@
 /*
 TEST_OUTPUT:
 ---
-fail_compilation/b17285.d(14): Error: type `ONE` has no value
-fail_compilation/b17285.d(14): Error: type `TWO` has no value
-fail_compilation/b17285.d(14): Error: cannot implicitly convert expression `ONE` of type `b17285.ONE` to `int`
+fail_compilation/b17285.d(15): Error: type `ONE` has no value
+fail_compilation/b17285.d(15):        perhaps use `ONE.init`
+fail_compilation/b17285.d(15): Error: type `TWO` has no value
+fail_compilation/b17285.d(15): Error: cannot implicitly convert expression `ONE` of type `b17285.ONE` to `int`
 ---
 */
 
diff --git a/compiler/test/fail_compilation/ice9545.d b/compiler/test/fail_compilation/ice9545.d
index 7360bc534f2a..b10e63987cf1 100644
--- a/compiler/test/fail_compilation/ice9545.d
+++ b/compiler/test/fail_compilation/ice9545.d
@@ -2,7 +2,8 @@
 /*
 TEST_OUTPUT:
 ----
-fail_compilation/ice9545.d(13): Error: type `int` has no value
+fail_compilation/ice9545.d(14): Error: type `int` has no value
+fail_compilation/ice9545.d(14):        perhaps use `int.init`
 ----
 */
 
diff --git a/compiler/test/fail_compilation/test20763.d b/compiler/test/fail_compilation/test20763.d
new file mode 100644
index 000000000000..786f8d895abd
--- /dev/null
+++ b/compiler/test/fail_compilation/test20763.d
@@ -0,0 +1,31 @@
+/*
+REQUIRED_ARGS: -de
+
+TEST_OUTPUT:
+---
+fail_compilation/test20763.d(25): Deprecation: type `ulong` has no value
+fail_compilation/test20763.d(25):        perhaps use `ulong.init`
+fail_compilation/test20763.d(26): Deprecation: type `ulong` has no value
+fail_compilation/test20763.d(26):        perhaps use `ulong.init`
+fail_compilation/test20763.d(27): Error: type `ulong` has no value
+fail_compilation/test20763.d(27):        perhaps use `ulong.init`
+fail_compilation/test20763.d(28): Error: type `ulong` has no value
+fail_compilation/test20763.d(28):        perhaps use `ulong.init`
+fail_compilation/test20763.d(29): Error: type `ulong` has no value
+fail_compilation/test20763.d(29):        perhaps use `ulong.init`
+fail_compilation/test20763.d(30): Error: type `ulong` has no value
+fail_compilation/test20763.d(30):        perhaps use `ulong.init`
+---
+*/
+
+// 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);
+}