go/ssa: support direct references to embedded fields in struct lit

h9jiang · h9jiang · commit 8e51a5fb67f9 · 2026-04-09T05:34:23.000-07:00
For golang/go#78553 Change-Id: If5a8fbeecefd13cd27848abea981fa95ff5a5d18 Reviewed-on: https://go-review.googlesource.com/c/tools/+/763920 Reviewed-by: Alan Donovan <adonovan@google.com> LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
diff --git a/go/ssa/builder.go b/go/ssa/builder.go
@@ -1275,7 +1275,7 @@ func (b *builder) arrayLen(fn *Function, elts []ast.Expr) int64 {
 //	x := T{a: 1}
 //	x = T{a: x.a}
 //
-// all the reads must occur before all the writes.  Thus all stores to
+// all the reads must occur before all the writes. Thus all stores to
 // loc are emitted to the storebuf sb for later execution.
 //
 // A CompositeLit may have pointer type only in the recursive (nested)
@@ -1292,28 +1292,35 @@ func (b *builder) compLit(fn *Function, addr Value, e *ast.CompositeLit, isZero
 			sb.store(&address{addr, e.Lbrace, nil}, zeroConst(zt))
 			isZero = true
 		}
+		var fIndices []int
 		for i, e := range e.Elts {
-			fieldIndex := i
-			pos := e.Pos()
-			if kv, ok := e.(*ast.KeyValueExpr); ok {
+			var (
+				pos   token.Pos
+				fType types.Type
+			)
+
+			if kv, ok := e.(*ast.KeyValueExpr); ok { // tagged field
 				fname := kv.Key.(*ast.Ident).Name
-				for i, n := 0, t.NumFields(); i < n; i++ {
-					sf := t.Field(i)
-					if sf.Name() == fname {
-						fieldIndex = i
-						pos = kv.Colon
-						e = kv.Value
-						break
-					}
-				}
+				obj, index, _ := types.LookupFieldOrMethod(t, true, fn.declaredPackage().Pkg, fname)
+				fIndices = append(fIndices[:0], index...)
+				pos = kv.Colon
+				e = kv.Value
+				fType = obj.Type()
+			} else { // untagged field
+				fIndices = append(fIndices[:0], i)
+				pos = e.Pos()
+				fType = t.Field(i).Type()
 			}
-			sf := t.Field(fieldIndex)
+
+			last := len(fIndices) - 1
+			v := emitImplicitSelections(fn, addr, fIndices[:last], pos)
+
 			faddr := &FieldAddr{
-				X:     addr,
-				Field: fieldIndex,
+				X:     v,
+				Field: fIndices[last],
 			}
 			faddr.setPos(pos)
-			faddr.setType(types.NewPointer(sf.Type()))
+			faddr.setType(types.NewPointer(fType))
 			fn.emit(faddr)
 			b.assign(fn, &address{addr: faddr, pos: pos, expr: e}, e, isZero, sb)
 		}
diff --git a/go/ssa/interp/interp_test.go b/go/ssa/interp/interp_test.go
@@ -141,6 +141,7 @@ var testdataTests = []string{
 	"slice2array.go",
 	"slice2arrayptr.go",
 	"static.go",
+	"structlitpromoted_go127.go",
 	"typeassert.go",
 	"width32.go",
 	"zeros.go",
diff --git a/go/ssa/interp/testdata/structlitpromoted_go127.go b/go/ssa/interp/testdata/structlitpromoted_go127.go
@@ -0,0 +1,28 @@
+// Copyright 2026 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build go1.27
+
+package main
+
+func main() {
+	// Test direct initialization of promoted fields in struct literals,
+	// introduced in go1.27. See golang/go#9859.
+	type Inner struct {
+		X int
+	}
+	type Outer struct {
+		Inner
+		Y int
+	}
+
+	o := Outer{
+		X: 1,
+		Y: 2,
+	}
+
+	if o.X != 1 || o.Y != 2 {
+		panic("failed to initialize promoted field")
+	}
+}
diff --git a/gopls/internal/test/marker/testdata/hover/issue78553.txt b/gopls/internal/test/marker/testdata/hover/issue78553.txt
@@ -0,0 +1,40 @@
+// This test verifies that hover works correctly on promoted fields
+// in struct composite literals (a Go 1.27 feature).
+
+-- flags --
+-min_go_command=go1.27
+
+-- go.mod --
+module mod.com
+
+go 1.27
+-- main.go --
+package main
+
+type E1 struct {
+	A int
+}
+
+type T struct {
+	E1
+}
+
+func main() {
+	_ = T{
+		A: 1,//@ hover("A", "A", a)
+	}
+
+	_ = T{
+		E1: E1{
+			A: 1,//@ hover("A", "A", a)
+		},
+	}
+}
+-- @a --
+```go
+field A int
+```
+
+---
+
+[`(main.E1).A` on pkg.go.dev](https://pkg.go.dev/mod.com#E1.A)
