[dev.typeparams] cmd/compile: fix getDictionarySym for methods references, write out sub-dictionaries

For method references (only), selectorExpr() now computes n.Selection,
which is the generic method that is selected. This allows us to compute
as needed the proper sub-dictionary for method reference. Also cleans up
some code for distinguishing method references from references to a
field that has a function value (especially in the presence of embedded
fields).

Change-Id: I9c5b789c15537ff48c70ca7a6444aa0420178a3a
Reviewed-on: https://go-review.googlesource.com/c/go/+/332095
Trust: Dan Scales <danscales@google.com>
Run-TryBot: Dan Scales <danscales@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>

1 files changed, 25 insertions, 4 deletions

diff --git a/src/cmd/compile/internal/noder/expr.go b/src/cmd/compile/internal/noder/expr.go
index 017e98986f..d974b291d0 100644
--- a/src/cmd/compile/internal/noder/expr.go
+++ b/src/cmd/compile/internal/noder/expr.go
@@ -206,6 +206,30 @@ func (g *irgen) selectorExpr(pos src.XPos, typ types2.Type, expr *syntax.Selecto
 		// only be fully transformed once it has an instantiated type.
 		n := ir.NewSelectorExpr(pos, ir.OXDOT, x, typecheck.Lookup(expr.Sel.Value))
 		typed(g.typ(typ), n)
+
+		// Fill in n.Selection for a generic method reference, even though we
+		// won't use it directly, since it is useful for analysis.
+		// Specifically do not fill in for fields or interfaces methods, so
+		// n.Selection being non-nil means a method reference, rather than an
+		// interface reference or reference to a field with a function value.
+		obj2 := g.info.Selections[expr].Obj()
+		sig := types2.AsSignature(obj2.Type())
+		if sig == nil || sig.Recv() == nil {
+			return n
+		}
+		// recvType is the type of the last embedded field. Because of the
+		// way methods are imported, g.obj(obj2) doesn't work across
+		// packages, so we have to lookup the method via the receiver type.
+		recvType := deref2(sig.Recv().Type())
+		if types2.AsInterface(recvType.Underlying()) != nil {
+			return n
+		}
+
+		index := g.info.Selections[expr].Index()
+		last := index[len(index)-1]
+		recvObj := types2.AsNamed(recvType).Obj()
+		recv := g.pkg(recvObj.Pkg()).Lookup(recvObj.Name()).Def
+		n.Selection = recv.Type().Methods().Index(last)
 		return n
 	}
 
@@ -308,10 +332,7 @@ func (g *irgen) selectorExpr(pos src.XPos, typ types2.Type, expr *syntax.Selecto
 
 // getTargs gets the targs associated with the receiver of a selected method
 func getTargs(selinfo *types2.Selection) []types2.Type {
-	r := selinfo.Recv()
-	if p := types2.AsPointer(r); p != nil {
-		r = p.Elem()
-	}
+	r := deref2(selinfo.Recv())
 	n := types2.AsNamed(r)
 	if n == nil {
 		base.Fatalf("Incorrect type for selinfo %v", selinfo)