Add -exclude flag and functionality

Author: kisielk

README.md

@@ -37,11 +37,27 @@ The `-blank` flag enables checking for assignments of errors to the
 blank identifier. It takes no arguments.
 
 
-## Whitelist
-errcheck has an internal whitelist for functions in the Go standard library that
+## Excluding functions
+
+Use the `-exclude` flag to specify a path to a file containing a list of functions to
+be excluded.
+
+    errcheck -exclude errcheck_excludes.txt path/to/package
+
+The file should contain one function signature per line. The format for function signatures is
+`package.FunctionName` while for methods it's `(package.Receiver).MethodName` for value receivers
+and `(*package.Receiver).MethodName` for pointer receivers.
+
+An example of an exclude file is:
+
+    io/ioutil.ReadFile
+    (*net/http.Client).Do
+
+The exclude list is combined with an internal list for functions in the Go standard library that
 have an error return type but are documented to never return an error.
 
-## Ignoring functions
+
+### The deprecated method
 
 The `-ignore` flag takes a comma-separated list of pairs of the form package:regex.
 For each package, the regex describes which functions to ignore within that package.

internal/errcheck/errcheck.go

@@ -106,6 +106,30 @@ type Checker struct {
 
 	// If true, checking of of _test.go files is disabled
 	WithoutTests bool
+
+	exclude map[string]bool
+}
+
+func NewChecker() *Checker {
+	c := Checker{}
+	c.SetExclude(map[string]bool{})
+	return &c
+}
+
+func (c *Checker) SetExclude(l map[string]bool) {
+	// Default exclude for stdlib functions
+	c.exclude = map[string]bool{
+		"math/rand.Read":         true,
+		"(*math/rand.Rand).Read": true,
+
+		"(*bytes.Buffer).Write":       true,
+		"(*bytes.Buffer).WriteByte":   true,
+		"(*bytes.Buffer).WriteRune":   true,
+		"(*bytes.Buffer).WriteString": true,
+	}
+	for k := range l {
+		c.exclude[k] = true
+	}
 }
 
 func (c *Checker) logf(msg string, args ...interface{}) {
@@ -160,6 +184,7 @@ func (c *Checker) CheckPackages(paths ...string) error {
 				blank:   c.Blank,
 				asserts: c.Asserts,
 				lines:   make(map[string][]string),
+				exclude: c.exclude,
 				errors:  []UncheckedError{},
 			}
 
@@ -186,22 +211,12 @@ type visitor struct {
 	blank   bool
 	asserts bool
 	lines   map[string][]string
+	exclude map[string]bool
 
 	errors []UncheckedError
 }
 
-func (v *visitor) builtinIgnoreCall(call *ast.CallExpr) bool {
-	// TODO(dh): find a better name for this method
-	ignored := map[string]bool{
-		"math/rand.Read":         true,
-		"(*math/rand.Rand).Read": true,
-
-		"(*bytes.Buffer).Write":       true,
-		"(*bytes.Buffer).WriteByte":   true,
-		"(*bytes.Buffer).WriteRune":   true,
-		"(*bytes.Buffer).WriteString": true,
-	}
-
+func (v *visitor) excludeCall(call *ast.CallExpr) bool {
 	sel, ok := call.Fun.(*ast.SelectorExpr)
 	if !ok {
 		return false
@@ -219,11 +234,11 @@ func (v *visitor) builtinIgnoreCall(call *ast.CallExpr) bool {
 	// want to support vendored stdlib packages, we need to implement
 	// FullName with our own logic.
 	name := fn.FullName()
-	return ignored[name]
+	return v.exclude[name]
 }
 
 func (v *visitor) ignoreCall(call *ast.CallExpr) bool {
-	if v.builtinIgnoreCall(call) {
+	if v.excludeCall(call) {
 		return true
 	}
 

internal/errcheck/errcheck_test.go

@@ -89,6 +89,10 @@ func TestAll(t *testing.T) {
 	test(t, CheckAsserts|CheckBlank)
 }
 
+func TestWhitelist(t *testing.T) {
+
+}
+
 const testVendorMain = `
 	package main
 
@@ -152,9 +156,8 @@ func TestIgnore(t *testing.T) {
 	}
 
 	for i, currCase := range cases {
-		checker := &Checker{
-			Ignore: currCase.ignore,
-		}
+		checker := NewChecker()
+		checker.Ignore = currCase.ignore
 		err := checker.CheckPackages(path.Join("github.com/kisielk/errcheck/internal/errcheck", testVendorDir))
 
 		if currCase.numExpectedErrs == 0 {
@@ -181,10 +184,9 @@ func test(t *testing.T, f flags) {
 		asserts bool = f&CheckAsserts != 0
 		blank   bool = f&CheckBlank != 0
 	)
-	checker := &Checker{
-		Asserts: asserts,
-		Blank:   blank,
-	}
+	checker := NewChecker()
+	checker.Asserts = asserts
+	checker.Blank = blank
 	err := checker.CheckPackages(testPackage)
 	uerr, ok := err.(*UncheckedErrors)
 	if !ok {

main.go

@@ -1,6 +1,7 @@
 package main
 
 import (
+	"bufio"
 	"flag"
 	"fmt"
 	"os"
@@ -102,7 +103,7 @@ func reportUncheckedErrors(e *errcheck.UncheckedErrors) {
 func mainCmd(args []string) int {
 	runtime.GOMAXPROCS(runtime.NumCPU())
 
-	checker := &errcheck.Checker{}
+	checker := errcheck.NewChecker()
 	paths, err := parseFlags(checker, args)
 	if err != exitCodeOk {
 		return err
@@ -137,13 +138,34 @@ func parseFlags(checker *errcheck.Checker, args []string) ([]string, int) {
 	ignore := ignoreFlag(map[string]*regexp.Regexp{
 		"fmt": dotStar,
 	})
-	flags.Var(ignore, "ignore", "comma-separated list of pairs of the form pkg:regex\n"+
-		"            the regex is used to ignore names within pkg")
+	flags.Var(ignore, "ignore", "[deprecated] comma-separated list of pairs of the form pkg:regex\n"+
+		"            the regex is used to ignore names within pkg.")
+
+	var excludeFile string
+	flags.StringVar(&excludeFile, "exclude", "", "Path to a file containing a list of functions to exclude from checking")
 
 	if err := flags.Parse(args[1:]); err != nil {
 		return nil, exitFatalError
 	}
 
+	if excludeFile != "" {
+		exclude := make(map[string]bool)
+		fh, err := os.Open(excludeFile)
+		if err != nil {
+			fmt.Fprintf(os.Stderr, "Could not read exclude file: %s\n", err)
+			return nil, exitFatalError
+		}
+		scanner := bufio.NewScanner(fh)
+		for scanner.Scan() {
+			exclude[scanner.Text()] = true
+		}
+		if err := scanner.Err(); err != nil {
+			fmt.Fprintf(os.Stderr, "Could not read exclude file: %s\n", err)
+			return nil, exitFatalError
+		}
+		checker.SetExclude(exclude)
+	}
+
 	checker.Tags = tags
 	for _, pkg := range strings.Split(*ignorePkg, ",") {
 		if pkg != "" {

main_test.go

@@ -54,7 +54,7 @@ func TestMain(t *testing.T) {
 		t.Errorf("Exit code is %d, expected %d", exitCode, exitUncheckedError)
 	}
 
-	expectUnchecked := 14
+	expectUnchecked := 15
 	if got := strings.Count(out, "UNCHECKED"); got != expectUnchecked {
 		t.Errorf("Got %d UNCHECKED errors, expected %d in:\n%s", got, expectUnchecked, out)
 	}

testdata/main.go

@@ -3,6 +3,7 @@ package main
 import (
 	"bytes"
 	"fmt"
+	"io/ioutil"
 	"math/rand"
 	mrand "math/rand"
 )
@@ -136,4 +137,6 @@ func main() {
 	b2.Write(nil)
 	rand.Read(nil)
 	mrand.Read(nil)
+
+	ioutil.ReadFile("main.go") // UNCHECKED
 }