quickfix/qf1002: emit valid fix for switches with initialization statements

Closes: gh-1613

Author: dominikh

quickfix/qf1002/qf1002.go

@@ -109,7 +109,7 @@ func run(pass *analysis.Pass) (interface{}, error) {
 
 			edits = append(edits, edit.ReplaceWithString(edit.Range{stmt.List[0].Pos(), stmt.Colon}, strings.Join(values, ", ")))
 		}
-		pos := swtch.Switch + token.Pos(len("switch"))
+		pos := swtch.Body.Lbrace
 		edits = append(edits, edit.ReplaceWithString(edit.Range{pos, pos}, " "+report.Render(pass, x)))
 		report.Report(pass, swtch, fmt.Sprintf("could use tagged switch on %s", report.Render(pass, x)),
 			report.Fixes(edit.Fix("Replace with tagged switch", edits...)))

quickfix/qf1002/testdata/go1.0/CheckTaglessSwitch/CheckTaglessSwitch.go

@@ -57,4 +57,11 @@ func fn1() {
 	switch {
 	case x == 1 && x == 2:
 	}
+
+	switch b := 42; { //@ diag(`could use tagged switch on b`)
+	case b == 0:
+	case b == 1:
+	default:
+		_ = b
+	}
 }

quickfix/qf1002/testdata/go1.0/CheckTaglessSwitch/CheckTaglessSwitch.go.golden

@@ -57,4 +57,11 @@ func fn1() {
 	switch {
 	case x == 1 && x == 2:
 	}
+
+	switch b := 42; b { //@ diag(`could use tagged switch on b`)
+	case 0:
+	case 1:
+	default:
+		_ = b
+	}
 }