Optimize memory for error case

New option SimpleErrorMessages that avoids allocation in the error path. It's off by default to preserve backwards compatibility.

Added benchmark BenchmarkBigParseAnyErrors that takes the big set of test cases, and injects errors to make them fail at pseudo-random places.

This optimization speeds up the error path runtime by 4x and reduces error path allocation bytes by 13x!

bench_test.go

@@ -71,9 +71,11 @@ func BenchmarkBigParseIn(b *testing.B) {
 
 func BenchmarkBigParseRetryAmbiguous(b *testing.B) {
 	b.ReportAllocs()
+	opts := []ParserOption{RetryAmbiguousDateWithSwap(true)}
+	b.ResetTimer()
 	for i := 0; i < b.N; i++ {
 		for _, t := range testInputs {
-			_, _ = ParseAny(t.in, RetryAmbiguousDateWithSwap(true))
+			_, _ = ParseAny(t.in, opts...)
 		}
 	}
 }
@@ -90,17 +92,48 @@ func BenchmarkShotgunParseErrors(b *testing.B) {
 
 func BenchmarkParseAnyErrors(b *testing.B) {
 	b.ReportAllocs()
+	opts := []ParserOption{SimpleErrorMessages(true)}
+	b.ResetTimer()
 	for i := 0; i < b.N; i++ {
 		for _, t := range testParseErrors {
-			_, _ = ParseAny(t.in)
+			_, _ = ParseAny(t.in, opts...)
+		}
+	}
+}
+
+func BenchmarkBigParseAnyErrors(b *testing.B) {
+	b.ReportAllocs()
+
+	opts := []ParserOption{SimpleErrorMessages(true)}
+	// manufacture a bunch of different tests with random errors put in them
+	var testBigErrorInputs []string
+	for index, t := range testInputs {
+		b := []byte(t.in)
+		spread := 4 + (index % 4)
+		startingIndex := spread % len(b)
+		for i := startingIndex; i < len(b); i += spread {
+			b[i] = '?'
+		}
+		testBigErrorInputs = append(testBigErrorInputs, string(b))
+	}
+	b.ResetTimer()
+
+	for i := 0; i < b.N; i++ {
+		for _, in := range testBigErrorInputs {
+			_, err := ParseAny(in, opts...)
+			if err == nil {
+				panic(fmt.Sprintf("expected parsing to fail: %s", in))
+			}
 		}
 	}
 }
 
 func BenchmarkParseAmbiguous(b *testing.B) {
 	b.ReportAllocs()
+	opts := []ParserOption{RetryAmbiguousDateWithSwap(true)}
+	b.ResetTimer()
 	for i := 0; i < b.N; i++ {
-		MustParse("13/02/2014 04:08:09 +0000 UTC", RetryAmbiguousDateWithSwap(true))
+		MustParse("13/02/2014 04:08:09 +0000 UTC", opts...)
 	}
 }