From 29ff25e70671ce2046aab5cf89bf519ec6cf2bed Mon Sep 17 00:00:00 2001
From: Iain Buclaw <ibuclaw@gdcproject.org>
Date: Tue, 8 Sep 2020 17:15:33 +0200
Subject: [PATCH] d: Warn when casting from a D class to a C++ class.

Before, the warning was only issued when casting in the other direction.
Now a warning is printed for both directions.

gcc/d/ChangeLog:

	* d-convert.cc (convert_expr): Warn when casting from a D class to a
	C++ class.

gcc/testsuite/ChangeLog:

	* gdc.dg/Waddress.d: New test.
	* gdc.dg/Wcastresult1.d: New test.
	* gdc.dg/Wcastresult2.d: New test.
---
 gcc/d/d-convert.cc                  |  4 ++--
 gcc/testsuite/gdc.dg/Waddress.d     | 12 ++++++++++++
 gcc/testsuite/gdc.dg/Wcastresult1.d | 18 ++++++++++++++++++
 gcc/testsuite/gdc.dg/Wcastresult2.d | 12 ++++++++++++
 4 files changed, 44 insertions(+), 2 deletions(-)
 create mode 100644 gcc/testsuite/gdc.dg/Waddress.d
 create mode 100644 gcc/testsuite/gdc.dg/Wcastresult1.d
 create mode 100644 gcc/testsuite/gdc.dg/Wcastresult2.d

diff --git a/gcc/d/d-convert.cc b/gcc/d/d-convert.cc
index 5e3e855b2cb..40e84f05347 100644
--- a/gcc/d/d-convert.cc
+++ b/gcc/d/d-convert.cc
@@ -430,10 +430,10 @@ convert_expr (tree exp, Type *etype, Type *totype)
 	      /* d_convert will make a no-op cast.  */
 	      break;
 	    }
-	  else if (cdfrom->isCPPclass ())
+	  else if (cdfrom->isCPPclass () || cdto->isCPPclass ())
 	    {
 	      /* Downcasting in C++ is a no-op.  */
-	      if (cdto->isCPPclass ())
+	      if (cdfrom->isCPPclass () && cdto->isCPPclass ())
 		break;
 
 	      /* Casting from a C++ interface to a class/non-C++ interface
diff --git a/gcc/testsuite/gdc.dg/Waddress.d b/gcc/testsuite/gdc.dg/Waddress.d
new file mode 100644
index 00000000000..74d7de80775
--- /dev/null
+++ b/gcc/testsuite/gdc.dg/Waddress.d
@@ -0,0 +1,12 @@
+// { dg-do compile }
+// { dg-options "-Waddress" }
+
+void* ptr;
+
+int test()
+{
+    if (&ptr) // { dg-warning "the address of 'ptr' will always evaluate as 'true'" }
+        return 1;
+
+    return 0;
+}
diff --git a/gcc/testsuite/gdc.dg/Wcastresult1.d b/gcc/testsuite/gdc.dg/Wcastresult1.d
new file mode 100644
index 00000000000..759b338acdc
--- /dev/null
+++ b/gcc/testsuite/gdc.dg/Wcastresult1.d
@@ -0,0 +1,18 @@
+// { dg-do compile }
+// { dg-options "-Wcast-result" }
+
+extern(C++) class CPPClass
+{
+    int a;
+}
+
+extern(D) class DClass
+{
+    int a;
+}
+
+void test()
+{
+    auto cpptod = cast(DClass)new CPPClass; // { dg-warning "cast to 'Wcastresult1.DClass' will produce null result" }
+    auto dtocpp = cast(CPPClass)new DClass; // { dg-warning "cast to 'Wcastresult1.CPPClass' will produce null result" }
+}
diff --git a/gcc/testsuite/gdc.dg/Wcastresult2.d b/gcc/testsuite/gdc.dg/Wcastresult2.d
new file mode 100644
index 00000000000..56d2dd20e82
--- /dev/null
+++ b/gcc/testsuite/gdc.dg/Wcastresult2.d
@@ -0,0 +1,12 @@
+// { dg-do compile }
+// { dg-options "-Wcast-result" }
+
+void test()
+{
+    auto imvalue = 1.23i;
+    auto revalue = 1.23;
+
+    auto imtore = cast(double)imvalue; // { dg-warning "cast from 'idouble' to 'double' will produce zero result" }
+    auto retoim = cast(idouble)revalue; // { dg-warning "cast from 'double' to 'idouble' will produce zero result" }
+    return;
+}
-- 
2.30.2