test(docs): add tests for examples in website hero and repo README

[eitsupi]

This PR renames the website tests to docs tests and adds more tests for examples in docs.

[eitsupi]

Wow, it seems the new test to have suddenly discovered an error in the README example!

$ cargo run -p prqlc compile
   Compiling prql-compiler v0.8.1 (/workspaces/prql/prql-compiler)
   Compiling prqlc v0.8.1 (/workspaces/prql/prql-compiler/prqlc)
    Finished dev [unoptimized + debuginfo] target(s) in 41.87s
     Running `target/debug/prqlc compile`
Enter PRQL, then press ctrl-d to compile:

from employees
filter country == "USA"                       # Each line transforms the previous result
aggregate {                                   # `aggregate` reduces each column to a value
  max salary,
  min salary,
  count,                                      # Trailing commas are allowed
}
Error:
   ╭─[Root.prql:6:3]
   │
 6 │   count,                                      # Trailing commas are allowed
   │   ──┬──
   │     ╰──── function std.aggregate, param `columns` expected type `scalar`, but found type `array -> int`
   │
   │ Help: Have you forgotten an argument to function std.count?
   │
   │ Note: Type `scalar` expands to `int || float || bool || text || date || time || timestamp || null`
───╯

@aljazerzen Any thoughts?

[aljazerzen]

Yeah, I changed count to require the non_null argument. I don't like it and it breaks a lot of queries, so I intend to revert that before release.

[eitsupi]

It seems that the default argument used to be set to *.
Is there any reason why this cannot be restored? (Just curious)

prql/prql-compiler/src/sql/std_impl.prql

Line 7 in 26cd9af

let count = non_null:s"*" -> <scalar || column> s"COUNT({non_null})"

[aljazerzen]

I needed it like that because I was changing how types work, and when a function is deemed a window function. It's an implementation thing.

[max-sixty]

Clever regex-ing!

In a way this is similar to

prql/web/book/tests/snapshot.rs

Line 152 in 65706a1

fn collect_book_examples() -> Result<Vec<Example>> {

, but easier to have this separate given they're in different places

[max-sixty]

I added a comment with a ref

[eitsupi]

I was initially thinking of code block analysis using pulldown-cmark, but changed because it seemed like overkill. (And extracting code blocks with pulldown-cmark was too difficult for me!)

[max-sixty]

Yeah I def think writing another parser wouldn't be great!

This code is a very good balance IMO

[max-sixty]

FWIW Rust unfortunately has poor performance with making lots of test binaries. So it would be faster if we could have this as a file within this test https://github.com/PRQL/prql/blob/65706a115a84997c608eaeda38b1aef1240fcec3/web/book/tests/snapshot.rs (which would change to a module, like this file is)

See the link at

prql/prql-compiler/tests/integration/README.md

Lines 54 to 55 in f4eb8c7

	We follow the advice in
	<https://matklad.github.io/2021/02/27/delete-cargo-integration-tests.html>.

(but we can merge this and make the change / I'll make the change, I don't want to slow you down!)