Running `cargo publish` from a non-colocated repo (such as my usual
repo) is currently quite scary because it uploads all non-hidden
files, even if they're ignored by `.gitignore`
(https://github.com/rust-lang/cargo/issues/2063). I noticed this a
while ago and have always run the command from a fresh clone since
then. To avoid the need for that, let's use the workaround mentioned
on the bug, which is to explicitly list patterns we want to publish.
Consider this code:
```
struct NoContentHash {}
#[derive(ContentHash)]
enum Hashable {
NoCanHash(NoContentHash),
Empty,
}
```
Before this commit, it generates an error like this:
```
error[E0277]: the trait bound `NoContentHash: ContentHash` is not satisfied
--> lib/src/content_hash.rs:150:10
|
150 | #[derive(ContentHash)]
| ^^^^^^^^^^^ the trait `ContentHash` is not implemented for `NoContentHash`
151 | enum Hashable {
152 | NoCanHash(NoContentHash),
| --------- required by a bound introduced by this call
|
= help: the following other types implement trait `ContentHash`:
bool
i32
i64
u8
u32
u64
std::collections::HashMap<K, V>
BTreeMap<K, V>
and 35 others
For more information about this error, try `rustc --explain E0277`.
```
After this commit, it generates a better error message:
```
error[E0277]: the trait bound `NoContentHash: ContentHash` is not satisfied
--> lib/src/content_hash.rs:152:15
|
152 | NoCanHash(NoContentHash),
| ^^^^^^^^^^^^^ the trait `ContentHash` is not implemented for `NoContentHash`
|
= help: the following other types implement trait `ContentHash`:
bool
i32
i64
u8
u32
u64
std::collections::HashMap<K, V>
BTreeMap<K, V>
and 35 others
For more information about this error, try `rustc --explain E0277`.
error: could not compile `jj-lib` (lib) due to 1 previous error
```
It also works for enum variants with named fields:
```
error[E0277]: the trait bound `NoContentHash: ContentHash` is not satisfied
--> lib/src/content_hash.rs:152:23
|
152 | NoCanHash { named: NoContentHash },
| ^^^^^^^^^^^^^ the trait `ContentHash` is not implemented for `NoContentHash`
|
= help: the following other types implement trait `ContentHash`:
bool
i32
i64
u8
u32
u64
std::collections::HashMap<K, V>
BTreeMap<K, V>
and 35 others
For more information about this error, try `rustc --explain E0277`.
```
This is a no-op in terms of function, but provides a nicer way to derive the
ContentHash trait for structs using the `#[derive(ContentHash)]` syntax used
for other traits such as `Debug`.
This commit only adds the macro. A subsequent commit will replace uses of
`content_hash!{}` with `#[derive(ContentHash)]`.
The new macro generates nice error messages, just like the old macro:
```
error[E0277]: the trait bound `NotImplemented: content_hash::ContentHash` is not satisfied
--> lib/src/content_hash.rs:265:16
|
265 | z: NotImplemented,
| ^^^^^^^^^^^^^^ the trait `content_hash::ContentHash` is not implemented for `NotImplemented`
|
= help: the following other types implement trait `content_hash::ContentHash`:
bool
i32
i64
u8
u32
u64
std::collections::HashMap<K, V>
BTreeMap<K, V>
and 38 others
```
This commit does two things to make proc macros re-exported by jj_lib useable
by deps:
1. jj_lib needs to be able refer to itself as `jj_lib` which it does
by adding an `extern crate self as jj_lib` declaration.
2. jj_lib::content_hash needs to re-export the `digest::Update` type so that
users of jj_lib can use the `#[derive(ContentHash)]` proc macro without
directly depending on the digest crate. This is done by re-exporting it
as `DigestUpdate`.
#3054
