Incremental compilation causes build to fail

[vipentti]

Currently when editing crates that contain / use salsa? related things, compilation may fail.

I have noticed this when editing ra_ide_api and ra_batch crates. This may occur with other crates as well.

This issue is not directly caused by rust-analyzer, however since it keeps occurring when working on the the project I thought it may be useful to have a tracking issue here as well.

This is reported in rust-lang/rust#58291

Current solution is to delete incremental compilation files for the particular project that reports the issues.

e.g on Linux when ra_batch fails to compile.

$ rm -rf ./target/debug/incremental/ra_batch-*

On Windows using cmd:

$ for /d %a in (.\target\debug\incremental\ra_batch-*) do rd /s /q %a

Simply change ra_batch-* to ra_ide_api-* when ra_ide_api fails to compile. This may occur in release as well, in that case change debug to release.

Example output of the error:

ra_ide_api

```
error[E0599]: no method named `parse` found for type `&db::RootDatabase` in the current scope
--> crates\ra_ide_api\src\call_info.rs:15:19
|
15 |     let file = db.parse(position.file_id);
|                   ^^^^^
|
= note: the method `parse` exists but the following trait bounds were not satisfied:
        `db::RootDatabase : ra_db::SourceDatabase`
        `&db::RootDatabase : ra_db::SourceDatabase`
        `db::RootDatabase : ra_db::SourceDatabase`
= help: items from traits can only be used if the trait is implemented and in scope
= note: the following trait defines an item `parse`, perhaps you need to implement it:
        candidate #1: `ra_db::SourceDatabase`

error[E0599]: no method named `parse` found for type `&db::RootDatabase` in the current scope
--> crates\ra_ide_api\src\call_info.rs:25:22
|
25 |     let fn_file = db.parse(symbol.file_id);
|                      ^^^^^
|
= note: the method `parse` exists but the following trait bounds were not satisfied:
        `db::RootDatabase : ra_db::SourceDatabase`
        `&db::RootDatabase : ra_db::SourceDatabase`
        `db::RootDatabase : ra_db::SourceDatabase`
= help: items from traits can only be used if the trait is implemented and in scope
= note: the following trait defines an item `parse`, perhaps you need to implement it:
        candidate #1: `ra_db::SourceDatabase`

error: aborting due to 2 previous errors

For more information about this error, try `rustc --explain E0599`.
error: Could not compile `ra_ide_api`.

To learn more, run the command again with --verbose.
```

ra_batch

```
error[E0599]: no method named `set_crate_graph` found for type `BatchDatabase` in the current scope
--> crates\ra_batch\src\lib.rs:90:12
|
22 | pub struct BatchDatabase {
| ------------------------ method `set_crate_graph` not found for this
...
90 |         db.set_crate_graph(Arc::new(crate_graph));
|            ^^^^^^^^^^^^^^^
|
= note: the method `set_crate_graph` exists but the following trait bounds were not satisfied:
        `BatchDatabase : ra_db::SourceDatabase`
= help: items from traits can only be used if the trait is implemented and in scope
= note: the following trait defines an item `set_crate_graph`, perhaps you need to implement it:
        candidate #1: `ra_db::SourceDatabase`

error[E0599]: no method named `set_file_text` found for type `BatchDatabase` in the current scope
--> crates\ra_batch\src\lib.rs:110:32
    |
22  | pub struct BatchDatabase {
    | ------------------------ method `set_file_text` not found for this
...
110 |                             db.set_file_text(file_id, text);
    |                                ^^^^^^^^^^^^^
    |
    = note: the method `set_file_text` exists but the following trait bounds were not satisfied:
            `BatchDatabase : ra_db::SourceDatabase`
    = help: items from traits can only be used if the trait is implemented and in scope
    = note: the following trait defines an item `set_file_text`, perhaps you need to implement it:
            candidate #1: `ra_db::SourceDatabase`

error[E0599]: no method named `set_file_relative_path` found for type `BatchDatabase` in the current scope
--> crates\ra_batch\src\lib.rs:111:32
    |
22  | pub struct BatchDatabase {
    | ------------------------ method `set_file_relative_path` not found for this
...
111 |                             db.set_file_relative_path(file_id, path.clone());
    |                                ^^^^^^^^^^^^^^^^^^^^^^
    |
    = note: the method `set_file_relative_path` exists but the following trait bounds were not satisfied:
            `BatchDatabase : ra_db::SourceDatabase`
    = help: items from traits can only be used if the trait is implemented and in scope
    = note: the following trait defines an item `set_file_relative_path`, perhaps you need to implement it:
            candidate #1: `ra_db::SourceDatabase`

error[E0599]: no method named `set_file_source_root` found for type `BatchDatabase` in the current scope
--> crates\ra_batch\src\lib.rs:112:32
    |
22  | pub struct BatchDatabase {
    | ------------------------ method `set_file_source_root` not found for this
...
112 |                             db.set_file_source_root(file_id, source_root_id);
    |                                ^^^^^^^^^^^^^^^^^^^^
    |
    = note: the method `set_file_source_root` exists but the following trait bounds were not satisfied:
            `BatchDatabase : ra_db::SourceDatabase`
    = help: items from traits can only be used if the trait is implemented and in scope
    = note: the following trait defines an item `set_file_source_root`, perhaps you need to implement it:
            candidate #1: `ra_db::SourceDatabase`

error[E0599]: no method named `set_source_root` found for type `BatchDatabase` in the current scope
--> crates\ra_batch\src\lib.rs:116:28
    |
22  | pub struct BatchDatabase {
    | ------------------------ method `set_source_root` not found for this
...
116 |                         db.set_source_root(source_root_id, Arc::new(source_root));
    |                            ^^^^^^^^^^^^^^^
    |
    = note: the method `set_source_root` exists but the following trait bounds were not satisfied:
            `BatchDatabase : ra_db::SourceDatabase`
    = help: items from traits can only be used if the trait is implemented and in scope
    = note: the following trait defines an item `set_source_root`, perhaps you need to implement it:
            candidate #1: `ra_db::SourceDatabase`

error: aborting due to 5 previous errors

For more information about this error, try `rustc --explain E0599`.
error: Could not compile `ra_batch`.

To learn more, run the command again with --verbose.
```

[kjeremy]

A slightly different one rust-lang/rust#58188