[vt/sqlparser] Use strings.Builder in compliantName

[LK4D4]

It halves allocations.
I would like to use it for Myprintf also very much, but I definitely need more research :)

[sougou]

Oh. Very nice! Any benchmarks?

[LK4D4]

@sougou nope, nothing in sqlparser benchmarks shows any difference :)
But strings builder is basically bytes.Buffer which can be used only once because it uses unsafe trick to not allocate string on String():
https://golang.org/src/strings/builder.go?s=1379:1412#L36
It was made for such cases.

[LK4D4]

@sougou
I wrote

+
+func BenchmarkCompliantName(b *testing.B) {
+       testString := ".ab"
+       for i := 0; i < b.N; i++ {
+               _ = NewColIdent(testString).CompliantName()
+               _ = NewTableIdent(testString).CompliantName()
+       }
+}

Results are:

benchmark                    old ns/op     new ns/op     delta
BenchmarkCompliantName-8     231           75.8          -67.19%

benchmark                    old allocs     new allocs     delta
BenchmarkCompliantName-8     4              2              -50.00%

benchmark                    old bytes     new bytes     delta
BenchmarkCompliantName-8     230           16            -93.04%

[slanning]

Note that this requires go 1.10+
(1.9: "go/vt/sqlparser/ast.go:3694:10: undefined: strings.Builder";
https://golang.org/pkg/strings/#Builder )
bootstrap.sh only requires that go version doesn't fail, though some docs mention installing 1.11+