Merge upstream stable

dmd/expressionsem.d

@@ -5274,7 +5274,12 @@ private extern (C++) final class ExpressionSemanticVisitor : Visitor
                     // Perturb the name mangling so that the symbols can co-exist
                     // instead of colliding
                     s.localNum = cast(ushort)(originalSymbol.localNum + 1);
-                    assert(s.localNum);         // 65535 should be enough for anyone
+                    // 65535 should be enough for anyone
+                    if (!s.localNum)
+                    {
+                        e.error("more than 65535 symbols with name `%s` generated", s.ident.toChars());
+                        return setError();
+                    }
 
                     // Replace originalSymbol with s, which updates the localCount
                     sc.func.localsymtab.update(s);

dmd/mtype.d

@@ -6374,7 +6374,7 @@ extern (C++) final class TypeClass : Type
         /* Conversion derived to const(base)
          */
         int offset = 0;
-        if (to.isBaseOf(this, &offset) && offset == 0 && MODimplicitConv(mod, to.mod))
+        if (to.isBaseOf(this, &offset) && MODimplicitConv(mod, to.mod))
         {
             // Disallow:
             //  derived to base

dmd/vsoptions.d

@@ -438,11 +438,17 @@ public:
     */
     const(char)* getVCLibDir(bool x64) const
     {
+        const(char)* proposed;
+
         if (VCToolsInstallDir !is null)
-            return FileName.combine(VCToolsInstallDir, x64 ? r"lib\x64" : r"lib\x86");
-        if (VCInstallDir !is null)
-            return FileName.combine(VCInstallDir, x64 ? r"lib\amd64" : "lib");
-        return null;
+            proposed = FileName.combine(VCToolsInstallDir, x64 ? r"lib\x64" : r"lib\x86");
+        else if (VCInstallDir !is null)
+            proposed = FileName.combine(VCInstallDir, x64 ? r"lib\amd64" : "lib");
+
+        // Due to the possibility of VS being installed with VC directory without the libraries
+        // we must check that the expected directory does exist.
+        // It is possible that this isn't the only location a file check is required.
+        return FileName.exists(proposed) ? proposed : null;
     }
 
     /**