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Niko Matsakis 2017-01-25 15:56:30 -05:00
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src/librustc/dep_graph/README.md
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@ -422,24 +422,3 @@ to see something like:
That first edge looks suspicious to you. So you set
`RUST_FORBID_DEP_GRAPH_EDGE` to `Hir&foo -> Collect&bar`, re-run, and
then observe the backtrace. Voila, bug fixed!
### Inlining of HIR nodes
For the time being, at least, we still sometimes "inline" HIR nodes
from other crates into the current HIR map. This creates a weird
scenario where the same logical item (let's call it `X`) has two
def-ids: the original def-id `X` and a new, inlined one `X'`. `X'` is
in the current crate, but it's not like other HIR nodes: in
particular, when we restart compilation, it will not be available to
hash. Therefore, we do not want `Hir(X')` nodes appearing in our
graph. Instead, we want a "read" of `Hir(X')` to be represented as a
read of `MetaData(X)`, since the metadata for `X` is where the inlined
representation originated in the first place.
To achieve this, the HIR map will detect if the def-id originates in
an inlined node and add a dependency to a suitable `MetaData` node
instead. If you are reading a HIR node and are not sure if it may be
inlined or not, you can use `tcx.map.read(node_id)` and it will detect
whether the node is inlined or not and do the right thing. You can
also use `tcx.map.is_inlined_def_id()` and
`tcx.map.is_inlined_node_id()` to test.