cmd/vet: implement old TODO from testdata/print.go

The code was fixed in CL 108559 but the testing TODO was not implemented.

Updates #22936

Change-Id: I20a703260a181bbcf5f87609d6fb8221a182be1a
Reviewed-on: https://go-review.googlesource.com/125038
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Rob Pike <r@golang.org>
Reviewed-by: Daniel Martí <mvdan@mvdan.cc>

src/cmd/vet/testdata/print.go

@@ -4,16 +4,10 @@
 
 // This file contains tests for the printf checker.
 
-// TODO(rsc): The user-defined wrapper tests are commented out
-// because they produced too many false positives when vet was
-// enabled during go test. See the TODO in ../print.go for a plan
-// to fix that; when it's fixed, uncomment the user-defined wrapper tests.
-
 package testdata
 
 import (
 	"fmt"
-	. "fmt"
 	logpkg "log" // renamed to make it harder to see
 	"math"
 	"os"
@@ -103,7 +97,7 @@ func PrintfTests() {
 	fmt.Printf("%s", stringerarrayv)
 	fmt.Printf("%v", notstringerarrayv)
 	fmt.Printf("%T", notstringerarrayv)
-	fmt.Printf("%d", new(Formatter))
+	fmt.Printf("%d", new(fmt.Formatter))
 	fmt.Printf("%*%", 2)               // Ridiculous but allowed.
 	fmt.Printf("%s", interface{}(nil)) // Nothing useful we can say.
 
@@ -250,13 +244,13 @@ func PrintfTests() {
 	t.Logf("%d", 3)
 	t.Logf("%d", "hi") // ERROR "Logf format %d has arg \x22hi\x22 of wrong type string"
 
-	// Errorf(1, "%d", 3)    // OK
-	// Errorf(1, "%d", "hi") // no error "Errorf format %d has arg \x22hi\x22 of wrong type string"
+	Errorf(1, "%d", 3)    // OK
+	Errorf(1, "%d", "hi") // ERROR "Errorf format %d has arg \x22hi\x22 of wrong type string"
 
 	// Multiple string arguments before variadic args
-	// errorf("WARNING", "foobar")            // OK
-	// errorf("INFO", "s=%s, n=%d", "foo", 1) // OK
-	// errorf("ERROR", "%d")                  // no error "errorf format %d reads arg #1, but call has 0 args"
+	errorf("WARNING", "foobar")            // OK
+	errorf("INFO", "s=%s, n=%d", "foo", 1) // OK
+	errorf("ERROR", "%d")                  // no error "errorf format %d reads arg #1, but call has 0 args"
 
 	// Printf from external package
 	// externalprintf.Printf("%d", 42) // OK
@@ -348,46 +342,32 @@ func (ss *someStruct) log(f func(), args ...interface{}) {}
 // A function we use as a function value; it has no other purpose.
 func someFunction() {}
 
-/*
 // Printf is used by the test so we must declare it.
 func Printf(format string, args ...interface{}) {
-	panic("don't call - testing only")
+	fmt.Printf(format, args...)
 }
 
 // Println is used by the test so we must declare it.
 func Println(args ...interface{}) {
-	panic("don't call - testing only")
-}
-
-// Logf is used by the test so we must declare it.
-func Logf(format string, args ...interface{}) {
-	panic("don't call - testing only")
+	fmt.Println(args...)
 }
 
-// Log is used by the test so we must declare it.
-func Log(args ...interface{}) {
-	panic("don't call - testing only")
-}
-*/
-
 // printf is used by the test so we must declare it.
 func printf(format string, args ...interface{}) {
-	panic("don't call - testing only")
+	fmt.Printf(format, args...)
 }
 
-/*
 // Errorf is used by the test for a case in which the first parameter
 // is not a format string.
 func Errorf(i int, format string, args ...interface{}) {
-	panic("don't call - testing only")
+	_ = fmt.Errorf(format, args...)
 }
 
 // errorf is used by the test for a case in which the function accepts multiple
 // string parameters before variadic arguments
 func errorf(level, format string, args ...interface{}) {
-	panic("don't call - testing only")
+	_ = fmt.Errorf(format, args...)
 }
-*/
 
 // multi is used by the test.
 func multi() []interface{} {

src/cmd/vet/vet_test.go

@@ -95,8 +95,7 @@ func TestVet(t *testing.T) {
 	}
 	batch := make([][]string, wide)
 	for i, file := range gos {
-		// TODO: Remove print.go exception once we require type checking for everything,
-		// and then delete TestVetPrint.
+		// The print.go test is run by TestVetPrint.
 		if strings.HasSuffix(file, "print.go") {
 			continue
 		}