[go] cmd/compile: adjust compiler to allow for embedded field selectors

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Robert Griesemer (Gerrit)

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Mar 16, 2026, 5:03:00 PM (3 days ago) Mar 16
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cmd/compile: adjust compiler to allow for embedded field selectors

WIP.
Change-Id: Ie314e28567cfa6cf4c9e962a07b32dd05b06bf5e

Change diff

diff --git a/src/cmd/compile/internal/typecheck/expr.go b/src/cmd/compile/internal/typecheck/expr.go
index 53c2912..10b7c82 100644
--- a/src/cmd/compile/internal/typecheck/expr.go
+++ b/src/cmd/compile/internal/typecheck/expr.go
@@ -312,6 +312,19 @@
 		return ir.NewStructKeyExpr(kv.Pos(), f, kv.Value)
 	}
 
+	var f *types.Field
+	if p, ambig := dotpath(sym, typ, &f, false); p != nil {
+		if ambig {
+			base.Errorf("ambiguous promoted field '%v' in struct literal of type %v", sym, typ)
+			return nil
+		}
+		if f.IsMethod() {
+			base.Errorf("cannot use method '%v' in struct literal of type %v", sym, typ)
+			return nil
+		}
+		return ir.NewStructKeyExpr(kv.Pos(), f, kv.Value)
+	}
+
 	if ci := Lookdot1(nil, sym, typ, typ.Fields(), 2); ci != nil { // Case-insensitive lookup.
 		if visible(ci.Sym) {
 			base.Errorf("unknown field '%v' in struct literal of type %v (but does have %v)", sym, typ, ci.Sym)
@@ -323,7 +336,6 @@
 		return nil
 	}
 
-	var f *types.Field
 	p, _ := dotpath(sym, typ, &f, true)
 	if p == nil || f.IsMethod() {
 		base.Errorf("unknown field '%v' in struct literal of type %v", sym, typ)
@@ -335,8 +347,8 @@
 	for ei := len(p) - 1; ei >= 0; ei-- {
 		ep = append(ep, p[ei].field.Sym.Name)
 	}
-	ep = append(ep, sym.Name)
-	base.Errorf("cannot use promoted field %v in struct literal of type %v", strings.Join(ep, "."), typ)
+	ep = append(ep, f.Sym.Name)
+	base.Errorf("unknown field '%v' in struct literal of type %v (but does have %v)", sym, typ, strings.Join(ep, "."))
 	return nil
 }
 
diff --git a/src/cmd/compile/internal/walk/complit.go b/src/cmd/compile/internal/walk/complit.go
index 1bc4d42..6f04a37 100644
--- a/src/cmd/compile/internal/walk/complit.go
+++ b/src/cmd/compile/internal/walk/complit.go
@@ -220,7 +220,7 @@
 				return ir.BlankNode, r.Value
 			}
 			ir.SetPos(r)
-			return ir.NewSelectorExpr(base.Pos, ir.ODOT, var_, r.Sym()), r.Value
+			return ir.NewSelectorExpr(base.Pos, ir.OXDOT, var_, r.Sym()), r.Value
 		}
 	default:
 		base.Fatalf("fixedlit bad op: %v", n.Op())
diff --git a/test/complit2.go b/test/complit2.go
new file mode 100644
index 0000000..43b23c0
--- /dev/null
+++ b/test/complit2.go
@@ -0,0 +1,37 @@
+// run
+
+// 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.
+
+// Verify that composite literals using selectors for
+// embedded fields are assembled correctly.
+
+package main
+
+import "fmt"
+
+type A struct {
+	a int
+	B
+}
+
+type B struct {
+	b string
+	C
+}
+
+type C struct {
+	c any
+}
+
+func main() {
+	eq(A{1, B{b: "foo"}}, A{a: 1, b: "foo"})
+	eq(A{B: B{C: C{c: "foo"}}}, A{c: "foo"})
+}
+
+func eq(x, y any) {
+	if x != y {
+		panic(fmt.Sprintf("%v != %v", x, y))
+	}
+}

Change information

Files:
  • M src/cmd/compile/internal/typecheck/expr.go
  • M src/cmd/compile/internal/walk/complit.go
  • A test/complit2.go
Change size: M
Delta: 3 files changed, 53 insertions(+), 4 deletions(-)
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Robert Griesemer (Gerrit)

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Robert Griesemer (Gerrit)

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    Change information

    Commit message:
    cmd/compile: enable promoted field selectors as keys in struct literals

    Switch the generated UIR version from V2 to V3.
    Adjust cmd/compile/internal/types to accept promoted field selectors
    in composite literals.

    Fixes #9859.
    Change-Id: Ie314e28567cfa6cf4c9e962a07b32dd05b06bf5e
    Auto-Submit: Robert Griesemer <g...@google.com>
    Reviewed-by: Mark Freeman <markf...@google.com>
    Reviewed-by: Keith Randall <k...@golang.org>
    Files:
    • M src/cmd/compile/internal/noder/unified.go
    • M src/cmd/compile/internal/typecheck/expr.go
    • M src/cmd/compile/internal/walk/complit.go
    • A test/complit2.go
      Change size: M
      Delta: 4 files changed, 55 insertions(+), 6 deletions(-)
      Branch: refs/heads/master
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