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Add docs for logging of queries. #1350

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May 12, 2022
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Add docs for logging of queries. #1350

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Add docs for logging of queries.
ehuss May 9, 2022
97da13d
Make it clearer that queries have different arguments and where to fi…
ehuss May 10, 2022
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24 changes: 24 additions & 0 deletions src/tracing.md
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Expand Up @@ -60,6 +60,30 @@ still get a short message per ignored `do_mir_borrowck`, but none of the things
calls. This helps you in looking through the calls that are happening and helps you adjust
your regex if you mistyped it.

## Query level filters

Every [query](query.md) is automatically tagged with a logging span so that
you can display all log messages during the execution of the query. For
example, if you want to log everything during type checking:

```
RUSTC_LOG=[typeck]
```

The query arguments are included as a tracing field which means that you can
filter on the debug display of the arguments. For example, the `typeck` query
has an argument `key: LocalDefId` of what is being checked. You can use a
regex to match on that `LocalDefId` to log type checking for a specific
function:

```
RUSTC_LOG=[typeck{key=.*name_of_item.*}]
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The argument name (key) is not the same in all queries, maybe point to https://github.com/rust-lang/rust/blob/87fd70c107b23fe08336a12a20a0f5e85561d499/compiler/rustc_middle/src/query/mod.rs#L18 so that people can browse the list of queries and see their arguments?

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good point! I pushed an update to try to make that clearer.

```

Different queries have different arguments. You can find a list of queries and
their arguments in
[`rustc_middle/src/query/mod.rs`](https://github.com/rust-lang/rust/blob/master/compiler/rustc_middle/src/query/mod.rs#L18).

## Broad module level filters

You can also use filters similar to the `log` crate's filters, which will enable
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