go/analysis: remove stray print statement in the timeformat analyzer

A debugging print statement was left in the analyzer, which breaks
gopls' communication over stdin/stdout.

Fix this, and add tests.

Fixes golang/vscode-go#2406

Change-Id: I1b785fa09e66eae2f1b1e03806e5b59d2015e75e
Reviewed-on: https://go-review.googlesource.com/c/tools/+/422902
TryBot-Result: Gopher Robot <gobot@golang.org>
gopls-CI: kokoro <noreply+kokoro@google.com>
Run-TryBot: Robert Findley <rfindley@google.com>
Reviewed-by: Tim King <taking@google.com>

go/analysis/passes/timeformat/timeformat.go

@@ -7,7 +7,6 @@
 package timeformat
 
 import (
-	"fmt"
 	"go/ast"
 	"go/constant"
 	"go/token"
@@ -59,7 +58,6 @@ func run(pass *analysis.Pass) (interface{}, error) {
 			if badAt > -1 {
 				// Check if it's a literal string, otherwise we can't suggest a fix.
 				if _, ok := arg.(*ast.BasicLit); ok {
-					fmt.Printf("%#v\n", arg)
 					pos := int(arg.Pos()) + badAt + 1 // +1 to skip the " or `
 					end := pos + len(badFormat)
 

gopls/internal/regtest/diagnostics/analysis_test.go

@@ -0,0 +1,54 @@
+// Copyright 2022 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.
+
+package diagnostics
+
+import (
+	"testing"
+
+	"golang.org/x/tools/internal/lsp/protocol"
+	. "golang.org/x/tools/internal/lsp/regtest"
+)
+
+// Test for the timeformat analyzer, following golang/vscode-go#2406.
+//
+// This test checks that applying the suggested fix from the analyzer resolves
+// the diagnostic warning.
+func TestTimeFormatAnalyzer(t *testing.T) {
+	const files = `
+-- go.mod --
+module mod.com
+
+go 1.18
+-- main.go --
+package main
+
+import (
+	"fmt"
+	"time"
+)
+
+func main() {
+	now := time.Now()
+	fmt.Println(now.Format("2006-02-01"))
+}`
+
+	Run(t, files, func(t *testing.T, env *Env) {
+		env.OpenFile("main.go")
+
+		var d protocol.PublishDiagnosticsParams
+		env.Await(
+			OnceMet(
+				env.DoneWithOpen(),
+				env.DiagnosticAtRegexp("main.go", "2006-02-01"),
+				ReadDiagnostics("main.go", &d),
+			),
+		)
+
+		env.ApplyQuickFixes("main.go", d.Diagnostics)
+		env.Await(
+			EmptyDiagnostics("main.go"),
+		)
+	})
+}

internal/lsp/testdata/analyzer/bad_test.go

@@ -4,6 +4,7 @@ import (
 	"fmt"
 	"sync"
 	"testing"
+	"time"
 )
 
 func Testbad(t *testing.T) { //@diag("", "tests", "Testbad has malformed name: first letter after 'Test' must not be lowercase", "warning")
@@ -16,3 +17,8 @@ func Testbad(t *testing.T) { //@diag("", "tests", "Testbad has malformed name: f
 func printfWrapper(format string, args ...interface{}) {
 	fmt.Printf(format, args...)
 }
+
+func _() {
+	now := time.Now()
+	fmt.Println(now.Format("2006-02-01")) //@diag("2006-02-01", "timeformat", "2006-02-01 should be 2006-01-02", "warning")
+}

internal/lsp/testdata/summary.txt.golden

@@ -8,7 +8,7 @@ DeepCompletionsCount = 5
 FuzzyCompletionsCount = 8
 RankedCompletionsCount = 164
 CaseSensitiveCompletionsCount = 4
-DiagnosticsCount = 37
+DiagnosticsCount = 38
 FoldingRangesCount = 2
 FormatCount = 6
 ImportCount = 8

internal/lsp/testdata/summary_go1.18.txt.golden

@@ -8,7 +8,7 @@ DeepCompletionsCount = 5
 FuzzyCompletionsCount = 8
 RankedCompletionsCount = 174
 CaseSensitiveCompletionsCount = 4
-DiagnosticsCount = 37
+DiagnosticsCount = 38
 FoldingRangesCount = 2
 FormatCount = 6
 ImportCount = 8