go.tools/cmd/vet: validate calls to t.Log and t.Logf

Be careful not to complain about math.Log and cmplx.Log.
Seems worthwhile since t.Log and t.Logf are often written but
rarely executed.

Nothing new turned up in the standard library.

Fixes golang/go#8504.

LGTM=josharian, dsymonds
R=golang-codereviews, josharian, dsymonds
CC=golang-codereviews
https://golang.org/cl/130490043

cmd/vet/doc.go

@@ -49,6 +49,7 @@ with these names, disregarding case:
 	Sprint Sprintf Sprintln
 	Error Errorf
 	Fatal Fatalf
+	Log Logf
 	Panic Panicf Panicln
 If the function name ends with an 'f', the function is assumed to take
 a format descriptor string in the manner of fmt.Printf. If not, vet

cmd/vet/print.go

@@ -35,6 +35,7 @@ var printfList = map[string]int{
 	"errorf":  0,
 	"fatalf":  0,
 	"fprintf": 1,
+	"logf":    0,
 	"panicf":  0,
 	"printf":  0,
 	"sprintf": 0,
@@ -47,6 +48,7 @@ var printList = map[string]int{
 	"error":  0,
 	"fatal":  0,
 	"fprint": 1, "fprintln": 1,
+	"log":   0,
 	"panic": 0, "panicln": 0,
 	"print": 0, "println": 0,
 	"sprint": 0, "sprintln": 0,
@@ -494,6 +496,18 @@ func (f *File) checkPrint(call *ast.CallExpr, name string, firstArg int) {
 	isLn := strings.HasSuffix(name, "ln")
 	isF := strings.HasPrefix(name, "F")
 	args := call.Args
+	if name == "Log" {
+		// Special case: Don't complain about math.Log or cmplx.Log.
+		// Not strictly necessary because the only complaint likely is for Log("%d")
+		// but it feels wrong to check that math.Log is a good print function.
+		if sel, ok := args[0].(*ast.SelectorExpr); ok {
+			if x, ok := sel.X.(*ast.Ident); ok {
+				if x.Name == "math" || x.Name == "cmplx" {
+					return
+				}
+			}
+		}
+	}
 	// check for Println(os.Stderr, ...)
 	if firstArg == 0 && !isF && len(args) > 0 {
 		if sel, ok := args[0].(*ast.SelectorExpr); ok {

cmd/vet/testdata/print.go

@@ -8,6 +8,7 @@ package testdata
 
 import (
 	"fmt"
+	"math"
 	"os"
 	"unsafe" // just for test case printing unsafe.Pointer
 )
@@ -197,6 +198,13 @@ func PrintfTests() {
 	Printf("%p %x", recursiveStruct1V, recursiveStruct1V.next)
 	Printf("%p %x", recursiveSliceV, recursiveSliceV)
 	Printf("%p %x", recursiveMapV, recursiveMapV)
+	// Special handling for Log.
+	math.Log(3)  // OK
+	Log(3)       // OK
+	Log("%d", 3) // ERROR "possible formatting directive in Log call"
+	Logf("%d", 3)
+	Logf("%d", "hi") // ERROR "arg .hi. for printf verb %d of wrong type: untyped string"
+
 }
 
 // Printf is used by the test so we must declare it.