gopls/internal/analysis: fix waitgroup modernizer formatting

Previously, the waitgroup modernizer directly printed the ast.Expr
for the receiver in the call to sync.WaitGroup.Go(). This resulted
in incorrect formatting when the sync.WaitGroup is inside a struct
type. Use printer.Fprint for formatting instead.

Fixes golang/go#74708

Change-Id: I32774163f309dcdd3d9f337898a6e0db3c9c0304
Reviewed-on: https://go-review.googlesource.com/c/tools/+/698155
Reviewed-by: Peter Weinberger <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>

Author: madelinekalil

gopls/internal/analysis/modernize/testdata/src/waitgroup/waitgroup.go

@@ -150,3 +150,35 @@ func _() {
 		wg1.Done()
 	}()
 }
+
+type Server struct {
+	wg sync.WaitGroup
+}
+
+type ServerContainer struct {
+	serv Server
+}
+
+func _() {
+	var s Server
+	s.wg.Add(1) // want "Goroutine creation can be simplified using WaitGroup.Go"
+	go func() {
+		print()
+		s.wg.Done()
+	}()
+
+	var sc ServerContainer
+	sc.serv.wg.Add(1) // want "Goroutine creation can be simplified using WaitGroup.Go"
+	go func() {
+		print()
+		sc.serv.wg.Done()
+	}()
+
+	var wg sync.WaitGroup
+	arr := [1]*sync.WaitGroup{&wg}
+	arr[0].Add(1) // want "Goroutine creation can be simplified using WaitGroup.Go"
+	go func() {
+		print()
+		arr[0].Done()
+	}()
+}

gopls/internal/analysis/modernize/testdata/src/waitgroup/waitgroup.go.golden

@@ -141,3 +141,32 @@ func _() {
 		wg1.Done()
 	}()
 }
+
+type Server struct {
+	wg sync.WaitGroup
+}
+
+type ServerContainer struct {
+	serv Server
+}
+
+func _() {
+	var s Server
+	// want "Goroutine creation can be simplified using WaitGroup.Go"
+	s.wg.Go(func() {
+		print()
+	})
+
+	var sc ServerContainer
+	// want "Goroutine creation can be simplified using WaitGroup.Go"
+	sc.serv.wg.Go(func() {
+		print()
+	})
+
+	var wg sync.WaitGroup
+	arr := [1]*sync.WaitGroup{&wg}
+	// want "Goroutine creation can be simplified using WaitGroup.Go"
+	arr[0].Go(func() {
+		print()
+	})
+}

gopls/internal/analysis/modernize/waitgroup.go

@@ -5,8 +5,10 @@
 package modernize
 
 import (
+	"bytes"
 	"fmt"
 	"go/ast"
+	"go/printer"
 	"slices"
 
 	"golang.org/x/tools/go/analysis"
@@ -108,6 +110,12 @@ func waitgroup(pass *analysis.Pass) {
 			continue
 		}
 
+		var addCallRecvText bytes.Buffer
+		err := printer.Fprint(&addCallRecvText, pass.Fset, addCallRecv)
+		if err != nil {
+			continue // error getting text for the edit
+		}
+
 		pass.Report(analysis.Diagnostic{
 			Pos:      addCall.Pos(),
 			End:      goStmt.End(),
@@ -127,7 +135,7 @@ func waitgroup(pass *analysis.Pass) {
 						{
 							Pos:     goStmt.Pos(),
 							End:     goStmt.Call.Pos(),
-							NewText: fmt.Appendf(nil, "%s.Go(", addCallRecv),
+							NewText: fmt.Appendf(nil, "%s.Go(", addCallRecvText.String()),
 						},
 						// ... }()
 						//      -