Improve code generation with text/template

[UserAB1236872]

Issues #30 and #29 are basically on hold because of some of the difficulty in rewriting the code generation. I think it would just plain be easier to rewrite the incredibly ad-hoc, ugly code gen script with text/template.

The new version likely would no longer use the Makefile, and instead directly generate the float64 version due to text/template's greater flexibility.

[dmitshur]

There's also go generate to consider.

[UserAB1236872]

That's coming in 1.4, right? I'm not too familiar with it, but the proposal I read simply allowed it to run arbitrary user-written code generation scripts, right? So doing this would still be necessary.

[dmitshur]

Yes, go generate is just a standard way for Go packages to run some commands to update their source code.

It's nice because it's a standard that's easy to follow and makes contributing to various Go packages easier. You know it's always go generate, rather than make or update_code.sh or run_regen or something else custom and non-standard.

See here for an example of replacing a bash file with go generate directives: gopherjs/websocket@c80adc1.

[alexvasi]

I tried to rewrite genprog using text/template. Only vectors for now. Here is the result:
alexvasi@1ed7256

The main idea was to place all crucial information directly in the template and not in the program that generates code. I know, I could have passed meta info about types and functions to template. Or I could have used sub-templates for each function for example. In the end I decided against it. Template almost looks like a go code, if you squint hard enough. And that's a good thing, I guess. Except maybe there will be float32/64 flag later.

First of all it works. It is a zero-diff change... well, not actually. The order of functions in vector.go is different now. It takes 10 or so additional lines in template to make the order the same. I dumped them. But that's how I tested new generator.

Here is some caveats:

• text/template is sloppy with whitespaces. I abused gofmt and it's called after template rendering.
• I changed template separators from {{ to <<. It is too many curly brackets in go code already.
• The readability of vector.tpl is not perfect.
• Broken diff. It is hard to validate new generator with changed functions order. I should add some tests for each vector function to vec_test.go anyway.