From: Matthew Dempsky <mdempsky@google.com>
Date: Mon, 17 May 2021 17:47:04 +0000 (-0700)
Subject: [dev.typeparams] cmd/compile/internal/types2: better recv Var for method expressions
X-Git-Tag: go1.18beta1~1818^2^2~531
X-Git-Url: http://www.git.cypherpunks.su/?a=commitdiff_plain;h=c92ae885d98d331ec489f6e705f2c5371e5f0e42;p=gostls13.git

[dev.typeparams] cmd/compile/internal/types2: better recv Var for method expressions

When synthesizing the Signature to represent a method expression, keep
as much of the original parameter as possible, substituting only the
receiver type.

Fixes #46209.

Change-Id: Ic4531820ae7d203bb0ba25a985f72d219b4aa25f
Reviewed-on: https://go-review.googlesource.com/c/go/+/320489
Trust: Matthew Dempsky <mdempsky@google.com>
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>
---

diff --git a/src/cmd/compile/internal/types2/call.go b/src/cmd/compile/internal/types2/call.go
index 6d149340b2..f0f769ec70 100644
--- a/src/cmd/compile/internal/types2/call.go
+++ b/src/cmd/compile/internal/types2/call.go
@@ -576,17 +576,23 @@ func (check *Checker) selector(x *operand, e *syntax.SelectorExpr) {
 
 		check.recordSelection(e, MethodExpr, x.typ, m, index, indirect)
 
+		sig := m.typ.(*Signature)
+		if sig.recv == nil {
+			check.error(e, "illegal cycle in method declaration")
+			goto Error
+		}
+
 		// the receiver type becomes the type of the first function
 		// argument of the method expression's function type
 		var params []*Var
-		sig := m.typ.(*Signature)
 		if sig.params != nil {
 			params = sig.params.vars
 		}
+		params = append([]*Var{NewVar(sig.recv.pos, sig.recv.pkg, sig.recv.name, x.typ)}, params...)
 		x.mode = value
 		x.typ = &Signature{
 			tparams:  sig.tparams,
-			params:   NewTuple(append([]*Var{NewVar(nopos, check.pkg, "_", x.typ)}, params...)...),
+			params:   NewTuple(params...),
 			results:  sig.results,
 			variadic: sig.variadic,
 		}
diff --git a/src/cmd/compile/internal/types2/testdata/check/decls0.src b/src/cmd/compile/internal/types2/testdata/check/decls0.src
index e78d8867e0..80bf4ebb3d 100644
--- a/src/cmd/compile/internal/types2/testdata/check/decls0.src
+++ b/src/cmd/compile/internal/types2/testdata/check/decls0.src
@@ -185,10 +185,10 @@ func f2(x *f2 /* ERROR "not a type" */ ) {}
 func f3() (x f3 /* ERROR "not a type" */ ) { return }
 func f4() (x *f4 /* ERROR "not a type" */ ) { return }
 
-func (S0) m1(x S0 /* ERROR value .* is not a type */ .m1) {}
-func (S0) m2(x *S0 /* ERROR value .* is not a type */ .m2) {}
-func (S0) m3() (x S0 /* ERROR value .* is not a type */ .m3) { return }
-func (S0) m4() (x *S0 /* ERROR value .* is not a type */ .m4) { return }
+func (S0) m1(x S0 /* ERROR illegal cycle in method declaration */ .m1) {}
+func (S0) m2(x *S0 /* ERROR illegal cycle in method declaration */ .m2) {}
+func (S0) m3() (x S0 /* ERROR illegal cycle in method declaration */ .m3) { return }
+func (S0) m4() (x *S0 /* ERROR illegal cycle in method declaration */ .m4) { return }
 
 // interfaces may not have any blank methods
 type BlankI interface {