x/tools: print check misses concatenated strings

Fixes golang/go#30436

Change-Id: I5b843e65b2188040a1ea5f17e1756b57babb0c22
GitHub-Last-Rev: 3ee8e18
GitHub-Pull-Request: #344
Reviewed-on: https://go-review.googlesource.com/c/tools/+/356830
Trust: Tim King <taking@google.com>
Trust: Zvonimir Pavlinovic <zpavlinovic@google.com>
Run-TryBot: Tim King <taking@google.com>
gopls-CI: kokoro <noreply+kokoro@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Zvonimir Pavlinovic <zpavlinovic@google.com>

Author: AlexanderYastrebov

go/analysis/passes/printf/printf.go

@@ -452,8 +452,15 @@ func stringConstantArg(pass *analysis.Pass, call *ast.CallExpr, idx int) (string
 	if idx >= len(call.Args) {
 		return "", false
 	}
-	arg := call.Args[idx]
-	lit := pass.TypesInfo.Types[arg].Value
+	return stringConstantExpr(pass, call.Args[idx])
+}
+
+// stringConstantExpr returns expression's string constant value.
+//
+// ("", false) is returned if expression isn't a string
+// constant.
+func stringConstantExpr(pass *analysis.Pass, expr ast.Expr) (string, bool) {
+	lit := pass.TypesInfo.Types[expr].Value
 	if lit != nil && lit.Kind() == constant.String {
 		return constant.StringVal(lit), true
 	}
@@ -1053,10 +1060,10 @@ func checkPrint(pass *analysis.Pass, call *ast.CallExpr, fn *types.Func) {
 	}
 
 	arg := args[0]
-	if lit, ok := arg.(*ast.BasicLit); ok && lit.Kind == token.STRING {
-		// Ignore trailing % character in lit.Value.
+	if s, ok := stringConstantExpr(pass, arg); ok {
+		// Ignore trailing % character
 		// The % in "abc 0.0%" couldn't be a formatting directive.
-		s := strings.TrimSuffix(lit.Value, `%"`)
+		s = strings.TrimSuffix(s, "%")
 		if strings.Contains(s, "%") {
 			m := printFormatRE.FindStringSubmatch(s)
 			if m != nil {
@@ -1067,9 +1074,8 @@ func checkPrint(pass *analysis.Pass, call *ast.CallExpr, fn *types.Func) {
 	if strings.HasSuffix(fn.Name(), "ln") {
 		// The last item, if a string, should not have a newline.
 		arg = args[len(args)-1]
-		if lit, ok := arg.(*ast.BasicLit); ok && lit.Kind == token.STRING {
-			str, _ := strconv.Unquote(lit.Value)
-			if strings.HasSuffix(str, "\n") {
+		if s, ok := stringConstantExpr(pass, arg); ok {
+			if strings.HasSuffix(s, "\n") {
 				pass.ReportRangef(call, "%s arg list ends with redundant newline", fn.FullName())
 			}
 		}

go/analysis/passes/printf/testdata/src/a/a.go

@@ -153,6 +153,7 @@ func PrintfTests() {
 	fmt.Println("%s", "hi")                     // want "fmt.Println call has possible formatting directive %s"
 	fmt.Println("%v", "hi")                     // want "fmt.Println call has possible formatting directive %v"
 	fmt.Println("%T", "hi")                     // want "fmt.Println call has possible formatting directive %T"
+	fmt.Println("%s"+" there", "hi")            // want "fmt.Println call has possible formatting directive %s"
 	fmt.Println("0.0%")                         // correct (trailing % couldn't be a formatting directive)
 	fmt.Printf("%s", "hi", 3)                   // want "fmt.Printf call needs 1 arg but has 2 args"
 	_ = fmt.Sprintf("%"+("s"), "hi", 3)         // want "fmt.Sprintf call needs 1 arg but has 2 args"
@@ -768,9 +769,10 @@ func UnexportedStringerOrError() {
 	fmt.Printf("%s", uei)       // want "Printf format %s has arg uei of wrong type a.unexportedErrorInterface"
 	fmt.Println("foo\n", "bar") // not an error
 
-	fmt.Println("foo\n")  // want "Println arg list ends with redundant newline"
-	fmt.Println("foo\\n") // not an error
-	fmt.Println(`foo\n`)  // not an error
+	fmt.Println("foo\n")      // want "Println arg list ends with redundant newline"
+	fmt.Println("foo" + "\n") // want "Println arg list ends with redundant newline"
+	fmt.Println("foo\\n")     // not an error
+	fmt.Println(`foo\n`)      // not an error
 
 	intSlice := []int{3, 4}
 	fmt.Printf("%s", intSlice) // want `fmt.Printf format %s has arg intSlice of wrong type \[\]int`