strconv: fix function name in errors for Atoi

Fixes #16980

Change-Id: I902a02b157c2c7d1772f5122b850dc48b1d7a224
Reviewed-on: https://go-review.googlesource.com/28474Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/strconv/atoi.go

@@ -199,6 +199,10 @@ func ParseInt(s string, base int, bitSize int) (i int64, err error) {
 
 // Atoi returns the result of ParseInt(s, 10, 0) converted to type int.
 func Atoi(s string) (int, error) {
+	const fnAtoi = "Atoi"
 	i64, err := ParseInt(s, 10, 0)
+	if nerr, ok := err.(*NumError); ok {
+		nerr.Func = fnAtoi
+	}
 	return int(i64), err
 }

src/strconv/strconv_test.go

@@ -55,3 +55,34 @@ func TestCountMallocs(t *testing.T) {
 		}
 	}
 }
+
+func TestErrorPrefixes(t *testing.T) {
+	_, errInt := Atoi("INVALID")
+	_, errBool := ParseBool("INVALID")
+	_, errFloat := ParseFloat("INVALID", 64)
+	_, errInt64 := ParseInt("INVALID", 10, 64)
+	_, errUint64 := ParseUint("INVALID", 10, 64)
+
+	vectors := []struct {
+		err  error  // Input error
+		want string // Function name wanted
+	}{
+		{errInt, "Atoi"},
+		{errBool, "ParseBool"},
+		{errFloat, "ParseFloat"},
+		{errInt64, "ParseInt"},
+		{errUint64, "ParseUint"},
+	}
+
+	for _, v := range vectors {
+		nerr, ok := v.err.(*NumError)
+		if !ok {
+			t.Errorf("test %s, error was not a *NumError", v.want)
+			continue
+		}
+		if got := nerr.Func; got != v.want {
+			t.Errorf("mismatching Func: got %s, want %s", got, v.want)
+		}
+	}
+
+}