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Clarify debugging graph dependency (#1862)

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Arthur Milchior 2024-01-27 21:42:06 +01:00 committed by GitHub
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src/incrcomp-debugging.md
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@ -2,13 +2,16 @@
## Testing the dependency graph ## Testing the dependency graph
There are various ways to write tests against the dependency graph. There are various ways to write tests against the dependency graph. The
The simplest mechanisms are the `#[rustc_if_this_changed]` and simplest mechanisms are the `#[rustc_if_this_changed]` and
`#[rustc_then_this_would_need]` annotations. These are used in ui tests `#[rustc_then_this_would_need]` annotations. These are used in [ui] tests to test
to test whether the expected set of paths exist in the dependency graph. whether the expected set of paths exist in the dependency graph.
As an example, see `tests/ui/dep-graph/dep-graph-caller-callee.rs`.
The idea is that you can annotate a test like: [`tests/ui/dep-graph/dep-graph-caller-callee.rs`]: https://github.com/rust-lang/rust/blob/master/tests/ui/dep-graph/dep-graph-caller-callee.rs
[ui]: tests/ui.html
As an example, see [`tests/ui/dep-graph/dep-graph-caller-callee.rs`], or the
tests below.
```rust,ignore ```rust,ignore
#[rustc_if_this_changed] #[rustc_if_this_changed]
@ -16,16 +19,24 @@ fn foo() { }
#[rustc_then_this_would_need(TypeckTables)] //~ ERROR OK #[rustc_then_this_would_need(TypeckTables)] //~ ERROR OK
fn bar() { foo(); } fn bar() { foo(); }
```
This should be read as
> If this (`foo`) is changed, then this (i.e. `bar`)'s TypeckTables would need
to be changed. Also, this
You could also add the lines
```rust,ignore
#[rustc_then_this_would_need(TypeckTables)] //~ ERROR no path #[rustc_then_this_would_need(TypeckTables)] //~ ERROR no path
fn baz() { } fn baz() { }
``` ```
This will check whether there is a path in the dependency graph from `Hir(foo)` Whose meaning is
to `TypeckTables(bar)`. An error is reported for each > If `foo` is changed, then `baz`'s TypeckTables does not need to be changed, as there is no path.
`#[rustc_then_this_would_need]` annotation that indicates whether a path
exists. `//~ ERROR` annotations can then be used to test if a path is found (as Recall that the `//~ ERROR OK` is a comment from the point of view of the Rust
demonstrated above). code we test, but is meaningful from the point of view of the test itself.
## Debugging the dependency graph ## Debugging the dependency graph