flag: return a consistent parse error if the flag value is invalid

Return a consistently formatted error string that reports either
a parse error or a range error.

Before:
	invalid boolean value "3" for -debug: strconv.ParseBool: parsing "3": invalid syntax

After:
	invalid boolean value "3" for -debug: parse error

Fixes #26822

Change-Id: I60992bf23da32a4c0cf32472a8af486a3c9674ad
Reviewed-on: https://go-review.googlesource.com/c/143257
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/flag/flag.go

@@ -83,6 +83,28 @@ import (
 // but no such flag is defined.
 var ErrHelp = errors.New("flag: help requested")
 
+// errParse is returned by Set if a flag's value fails to parse, such as with an invalid integer for Int.
+// It then gets wrapped through failf to provide more information.
+var errParse = errors.New("parse error")
+
+// errRange is returned by Set if a flag's value is out of range.
+// It then gets wrapped through failf to provide more information.
+var errRange = errors.New("value out of range")
+
+func numError(err error) error {
+	ne, ok := err.(*strconv.NumError)
+	if !ok {
+		return err
+	}
+	if ne.Err == strconv.ErrSyntax {
+		return errParse
+	}
+	if ne.Err == strconv.ErrRange {
+		return errRange
+	}
+	return err
+}
+
 // -- bool Value
 type boolValue bool
 
@@ -93,6 +115,9 @@ func newBoolValue(val bool, p *bool) *boolValue {
 
 func (b *boolValue) Set(s string) error {
 	v, err := strconv.ParseBool(s)
+	if err != nil {
+		err = errParse
+	}
 	*b = boolValue(v)
 	return err
 }
@@ -120,6 +145,9 @@ func newIntValue(val int, p *int) *intValue {
 
 func (i *intValue) Set(s string) error {
 	v, err := strconv.ParseInt(s, 0, strconv.IntSize)
+	if err != nil {
+		err = numError(err)
+	}
 	*i = intValue(v)
 	return err
 }
@@ -138,6 +166,9 @@ func newInt64Value(val int64, p *int64) *int64Value {
 
 func (i *int64Value) Set(s string) error {
 	v, err := strconv.ParseInt(s, 0, 64)
+	if err != nil {
+		err = numError(err)
+	}
 	*i = int64Value(v)
 	return err
 }
@@ -156,6 +187,9 @@ func newUintValue(val uint, p *uint) *uintValue {
 
 func (i *uintValue) Set(s string) error {
 	v, err := strconv.ParseUint(s, 0, strconv.IntSize)
+	if err != nil {
+		err = numError(err)
+	}
 	*i = uintValue(v)
 	return err
 }
@@ -174,6 +208,9 @@ func newUint64Value(val uint64, p *uint64) *uint64Value {
 
 func (i *uint64Value) Set(s string) error {
 	v, err := strconv.ParseUint(s, 0, 64)
+	if err != nil {
+		err = numError(err)
+	}
 	*i = uint64Value(v)
 	return err
 }
@@ -209,6 +246,9 @@ func newFloat64Value(val float64, p *float64) *float64Value {
 
 func (f *float64Value) Set(s string) error {
 	v, err := strconv.ParseFloat(s, 64)
+	if err != nil {
+		err = numError(err)
+	}
 	*f = float64Value(v)
 	return err
 }
@@ -227,6 +267,9 @@ func newDurationValue(val time.Duration, p *time.Duration) *durationValue {
 
 func (d *durationValue) Set(s string) error {
 	v, err := time.ParseDuration(s)
+	if err != nil {
+		err = errParse
+	}
 	*d = durationValue(v)
 	return err
 }

src/flag/flag_test.go

@@ -9,6 +9,7 @@ import (
 	. "flag"
 	"fmt"
 	"io"
+	"io/ioutil"
 	"os"
 	"sort"
 	"strconv"
@@ -491,3 +492,55 @@ func TestGetters(t *testing.T) {
 		t.Errorf("unexpected output: got %v, expected %v", fs.Output(), expectedOutput)
 	}
 }
+
+func TestParseError(t *testing.T) {
+	for _, typ := range []string{"bool", "int", "int64", "uint", "uint64", "float64", "duration"} {
+		fs := NewFlagSet("parse error test", ContinueOnError)
+		fs.SetOutput(ioutil.Discard)
+		_ = fs.Bool("bool", false, "")
+		_ = fs.Int("int", 0, "")
+		_ = fs.Int64("int64", 0, "")
+		_ = fs.Uint("uint", 0, "")
+		_ = fs.Uint64("uint64", 0, "")
+		_ = fs.Float64("float64", 0, "")
+		_ = fs.Duration("duration", 0, "")
+		// Strings cannot give errors.
+		args := []string{"-" + typ + "=x"}
+		err := fs.Parse(args) // x is not a valid setting for any flag.
+		if err == nil {
+			t.Errorf("Parse(%q)=%v; expected parse error", args, err)
+			continue
+		}
+		if !strings.Contains(err.Error(), "invalid") || !strings.Contains(err.Error(), "parse error") {
+			t.Errorf("Parse(%q)=%v; expected parse error", args, err)
+		}
+	}
+}
+
+func TestRangeError(t *testing.T) {
+	bad := []string{
+		"-int=123456789012345678901",
+		"-int64=123456789012345678901",
+		"-uint=123456789012345678901",
+		"-uint64=123456789012345678901",
+		"-float64=1e1000",
+	}
+	for _, arg := range bad {
+		fs := NewFlagSet("parse error test", ContinueOnError)
+		fs.SetOutput(ioutil.Discard)
+		_ = fs.Int("int", 0, "")
+		_ = fs.Int64("int64", 0, "")
+		_ = fs.Uint("uint", 0, "")
+		_ = fs.Uint64("uint64", 0, "")
+		_ = fs.Float64("float64", 0, "")
+		// Strings cannot give errors, and bools and durations do not return strconv.NumError.
+		err := fs.Parse([]string{arg})
+		if err == nil {
+			t.Errorf("Parse(%q)=%v; expected range error", arg, err)
+			continue
+		}
+		if !strings.Contains(err.Error(), "invalid") || !strings.Contains(err.Error(), "value out of range") {
+			t.Errorf("Parse(%q)=%v; expected range error", arg, err)
+		}
+	}
+}