d: Merge upstream dmd 0fcdaab32

Fixes a bug where there was undefined template references when compiling
upstream dmd mainline.

In `TemplateInstance::semantic`, there exists special handling of
matching template instances for the same template declaration to ensure
that only at most one instance gets codegen'd.

If the primary instance `inst` originated from a non-root module, the
`minst` field will be updated so it is now coming from a root module,
however all Dsymbol `inst->members` of the instance still have their
`_scope->minst` pointing at the original non-root module. We must now
propagate `minst` to all members so that forward referenced dependencies
that get instantiated will also be appended to the root module,
otherwise there will be undefined references at link-time.

This doesn't affect compilations where all modules are compiled
together, as every module is a root module in that situation.  What this
primarily affects are cases where there is a mix of root and non-root
modules, and a template was first instantiated in a non-root context,
then later instantiated again in a root context.

Reviewed-on: https://github.com/dlang/dmd/pull/11867

gcc/d/ChangeLog:

	* dmd/MERGE: Merge upstream dmd 0fcdaab32

2 files changed, 64 insertions, 4 deletions

diff --git a/gcc/d/dmd/MERGE b/gcc/d/dmd/MERGE
index 5f6193f..7b561e4 100644
--- a/gcc/d/dmd/MERGE
+++ b/gcc/d/dmd/MERGE
@@ -1,4 +1,4 @@
-70aabfb511d55f2bfbdccbac7868519d9d4b63da
+0fcdaab32c7645820820f6e1474343ccfb7560e5
 
 The first line of this file holds the git revision number of the last
 merge done from the dlang/dmd repository.
diff --git a/gcc/d/dmd/dtemplate.c b/gcc/d/dmd/dtemplate.c
index a86daee..caa8a5b 100644
--- a/gcc/d/dmd/dtemplate.c
+++ b/gcc/d/dmd/dtemplate.c
@@ -33,6 +33,7 @@
 #include "hdrgen.h"
 #include "id.h"
 #include "attrib.h"
+#include "cond.h"
 #include "tokens.h"
 
 #define IDX_NOTFOUND (0x12345678)               // index is not found
@@ -6088,17 +6089,18 @@ Lerror:
         if (minst && minst->isRoot() && !(inst->minst && inst->minst->isRoot()))
         {
             /* Swap the position of 'inst' and 'this' in the instantiation graph.
-             * Then, the primary instance `inst` will be changed to a root instance.
+             * Then, the primary instance `inst` will be changed to a root instance,
+             * along with all members of `inst` having their scopes updated.
              *
              * Before:
-             *  non-root -> A!() -> B!()[inst] -> C!()
+             *  non-root -> A!() -> B!()[inst] -> C!() { members[non-root] }
              *                      |
              *  root     -> D!() -> B!()[this]
              *
              * After:
              *  non-root -> A!() -> B!()[this]
              *                      |
-             *  root     -> D!() -> B!()[inst] -> C!()
+             *  root     -> D!() -> B!()[inst] -> C!() { members[root] }
              */
             Module *mi = minst;
             TemplateInstance *ti = tinst;
@@ -6107,6 +6109,64 @@ Lerror:
             inst->minst = mi;
             inst->tinst = ti;
 
+            /* https://issues.dlang.org/show_bug.cgi?id=21299
+               `minst` has been updated on the primary instance `inst` so it is
+               now coming from a root module, however all Dsymbol `inst.members`
+               of the instance still have their `_scope.minst` pointing at the
+               original non-root module. We must now propagate `minst` to all
+               members so that forward referenced dependencies that get
+               instantiated will also be appended to the root module, otherwise
+               there will be undefined references at link-time.  */
+            class InstMemberWalker : public Visitor
+            {
+            public:
+                TemplateInstance *inst;
+
+                InstMemberWalker(TemplateInstance *inst)
+                    : inst(inst) { }
+
+                void visit(Dsymbol *d)
+                {
+                    if (d->_scope)
+                        d->_scope->minst = inst->minst;
+                }
+
+                void visit(ScopeDsymbol *sds)
+                {
+                    if (!sds->members)
+                        return;
+                    for (size_t i = 0; i < sds->members->length; i++)
+                    {
+                        Dsymbol *s = (*sds->members)[i];
+                        s->accept(this);
+                    }
+                    visit((Dsymbol *)sds);
+                }
+
+                void visit(AttribDeclaration *ad)
+                {
+                    Dsymbols *d = ad->include(NULL);
+                    if (!d)
+                        return;
+                    for (size_t i = 0; i < d->length; i++)
+                    {
+                        Dsymbol *s = (*d)[i];
+                        s->accept(this);
+                    }
+                    visit((Dsymbol *)ad);
+                }
+
+                void visit(ConditionalDeclaration *cd)
+                {
+                    if (cd->condition->inc)
+                        visit((AttribDeclaration *)cd);
+                    else
+                        visit((Dsymbol *)cd);
+                }
+            };
+            InstMemberWalker v(inst);
+            inst->accept(&v);
+
             if (minst)  // if inst was not speculative
             {
                 /* Add 'inst' once again to the root module members[], then the