From 8e0c5f15e1f7b1339eec4befc9ed35a7e0a4aa88 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Daniel=20Mart=C3=AD?= <mvdan@mvdan.cc>
Date: Tue, 3 Jan 2023 21:48:36 +0100
Subject: [PATCH] syntax/typedjson: avoid MethodByName

We only used it with static method names,
so we can use type assertions to reach those methods instead.
This is easier as we avoid more reflection,
and does not throw off the linker's dead code elimination.

See https://github.com/dominikh/go-tools/issues/1348.
---
 syntax/typedjson/json.go | 21 ++++++++++-----------
 1 file changed, 10 insertions(+), 11 deletions(-)

diff --git a/syntax/typedjson/json.go b/syntax/typedjson/json.go
index e4a305a65..1fa659d5c 100644
--- a/syntax/typedjson/json.go
+++ b/syntax/typedjson/json.go
@@ -90,18 +90,17 @@ func encodeValue(val reflect.Value) (reflect.Value, string) {
 		encTyp := reflect.StructOf(fields)
 		enc := reflect.New(encTyp).Elem()
 
-		// Pos methods are defined on struct pointer receivers.
-		for i, name := range [...]string{"Pos", "End"} {
-			if fn := val.Addr().MethodByName(name); fn.IsValid() {
-				encodePos(enc.Field(1+i), fn.Call(nil)[0])
-			}
+		// Node methods are defined on struct pointer receivers.
+		if node, _ := val.Addr().Interface().(syntax.Node); node != nil {
+			encodePos(enc.Field(1), node.Pos()) // posField
+			encodePos(enc.Field(2), node.End()) // endField
 		}
 		// Do the rest of the fields.
 		for i := 3; i < encTyp.NumField(); i++ {
 			ftyp := encTyp.Field(i)
 			fval := val.FieldByName(ftyp.Name)
 			if ftyp.Type == exportedPosType {
-				encodePos(enc.Field(i), fval)
+				encodePos(enc.Field(i), fval.Interface().(syntax.Pos))
 			} else {
 				encElem, _ := encodeValue(fval)
 				if encElem.IsValid() {
@@ -173,17 +172,17 @@ type exportedPos struct {
 	Offset, Line, Col uint
 }
 
-func encodePos(encPtr, val reflect.Value) {
-	if !val.MethodByName("IsValid").Call(nil)[0].Bool() {
+func encodePos(encPtr reflect.Value, val syntax.Pos) {
+	if !val.IsValid() {
 		return
 	}
 	enc := reflect.New(exportedPosType.Elem())
 	encPtr.Set(enc)
 	enc = enc.Elem()
 
-	enc.Field(0).Set(val.MethodByName("Offset").Call(nil)[0])
-	enc.Field(1).Set(val.MethodByName("Line").Call(nil)[0])
-	enc.Field(2).Set(val.MethodByName("Col").Call(nil)[0])
+	enc.Field(0).SetUint(uint64(val.Offset()))
+	enc.Field(1).SetUint(uint64(val.Line()))
+	enc.Field(2).SetUint(uint64(val.Col()))
 }
 
 func decodePos(val reflect.Value, enc map[string]interface{}) {