Remove DocBuilder, part 1

[pietroalbini]

This PR is the first of the two PRs I plan to send to remove DocBuilder and DocBuilderOptions from the docs.rs codebase: both those structs serve as "intermediaries" between RustwideBuilder and the rest of the application, but now that we have Config and Context that's not really needed anymore. Not having the middle layer will help with building buildtests a lot.

Notable changes:

• cratesfyi build --skip-if-log-exists <command> was removed: the --skip-if-log-exists flag was really fragile, relying on a text log of all the builds updated every 10 builds. There is also no need I can see for it, as the practically equivalent (and better) --skip-if-exists already exists.
• cratesfyi build --skip-if-exists <command> was improved: now it checks if a successful build is present, instead of checking whether the release metadata is stored in the database.
• All the RustwideBuilder configuration was moved over to Config.
• All of DocBuilderOptions was moved over to Config.
• The Index is now stored in Context and a single instance is reused across the whole application. This won't affect the file descriptors problem, as the underlying git instance is still re-created every time it is accessed.

In the next PR I'll move away all the rest of DocBuilder. This PR is best reviewed commit-by-commit.

[jyn514]

I didn't know we had this 😆 do we know anyone using this? I'd rather have #809 I think.

[pietroalbini]

Dunno why it exists, but let's not remove it for now until we get more insights on who's using it.

[jyn514]

This needs an INNER JOIN or you'll get duplicates (the id won't match the crate that succeeded).

[pietroalbini]

Hmm? This is working as expected when testing manually. Why would you expect it to fail?

[jyn514]

Huh, I expected it to fail when you have three different crates, each of which satisfies one of these conditions.

CREATE TEMPORARY TABLE crates (
  id SERIAL PRIMARY KEY,
  name VARCHAR(255) UNIQUE NOT NULL
);

CREATE TEMPORARY TABLE releases (
   id SERIAL PRIMARY KEY,
   crate_id INT NOT NULL REFERENCES crates(id),
   version VARCHAR(100)
);

CREATE TEMPORARY TABLE builds (
   id SERIAL,
   rid INT NOT NULL REFERENCES releases(id),
   build_status BOOL NOT NULL
);

insert into crates (name) values ('a'), ('b');
insert into releases (crate_id, version) values (1, '0.1.0'), (2, '0.1.0');
insert into builds (rid, build_status) values (1, true), (2, true);

SELECT 1 FROM crates, releases, builds
WHERE crates.id = releases.crate_id AND releases.id = builds.rid
  AND crates.name = 'a' AND releases.version = '0.1.0'  AND builds.build_status = TRUE;

But that doesn't happen - the WHERE id = crate_id AND id = rid filters out the duplicates. It's more clear when you select everything instead of 1:

select * from crates, releases, builds WHERE crates.id = releases.crate_id AND releases.id = builds.rid;
 id | name | id | crate_id | version | id | rid | build_status 
----+------+----+----------+---------+----+-----+--------------
  1 | a    |  1 |        1 | 0.1.0   |  1 |   1 | f
  2 | b    |  2 |        2 | 0.1.0   |  2 |   2 | t
joshua=> select * from crates, releases, builds WHERE crates.name = 'a' AND releases.version = '0.1.0'  AND builds.build_status = TRUE;
 id | name | id | crate_id | version | id | rid | build_status 
----+------+----+----------+---------+----+-----+--------------
  1 | a    |  1 |        1 | 0.1.0   |  2 |   2 | t
  1 | a    |  2 |        2 | 0.1.0   |  2 |   2 | t
joshua=> select * from crates, releases, builds WHERE crates.name = 'a' AND releases.version = '0.1.0'  AND builds.build_status = TRUE AND crates.id = releases.crate_id AND releases.id = builds.rid;
 id | name | id | crate_id | version | id | rid | build_status 
----+------+----+----------+---------+----+-----+--------------
(0 rows)

So this works, it's just confusing.