Show a more informative panic message when `DefPathHash` does not exist
This should hopefully make it easier to debug incremental compilation
bugs like #93096 without affecting performance.
Fix star handling in block doc comments
Fixes#92872.
Some extra explanation about this PR and why https://github.com/rust-lang/rust/pull/92357 created this regression: when we merge doc comment kinds for example in:
```rust
/// he
/**
* hello
*/
#[doc = "boom"]
```
We don't want to remove the empty lines between them. However, to correctly compute the "horizontal trim", we still need it, so instead, I put back a part of the "vertical trim" directly in the "horizontal trim" computation so it doesn't impact the output buffer but allows us to correctly handle the stars.
r? ``@camelid``
Introduce drop range tracking to generator interior analysis
This PR addresses cases such as this one from #57478:
```rust
struct Foo;
impl !Send for Foo {}
let _: impl Send = || {
let guard = Foo;
drop(guard);
yield;
};
```
Previously, the `generator_interior` pass would unnecessarily include the type `Foo` in the generator because it was not aware of the behavior of `drop`. We fix this issue by introducing a drop range analysis that finds portions of the code where a value is guaranteed to be dropped. If a value is dropped at all suspend points, then it is no longer included in the generator type. Note that we are using "dropped" in a generic sense to include any case in which a value has been moved. That is, we do not only look at calls to the `drop` function.
There are several phases to the drop tracking algorithm, and we'll go into more detail below.
1. Use `ExprUseVisitor` to find values that are consumed and borrowed.
2. `DropRangeVisitor` uses consume and borrow information to gather drop and reinitialization events, as well as build a control flow graph.
3. We then propagate drop and reinitialization information through the CFG until we reach a fix point (see `DropRanges::propagate_to_fixpoint`).
4. When recording a type (see `InteriorVisitor::record`), we check the computed drop ranges to see if that value is definitely dropped at the suspend point. If so, we skip including it in the type.
## 1. Use `ExprUseVisitor` to find values that are consumed and borrowed.
We use `ExprUseVisitor` to identify the places where values are consumed. We track both the `hir_id` of the value, and the `hir_id` of the expression that consumes it. For example, in the expression `[Foo]`, the `Foo` is consumed by the array expression, so after the array expression we can consider the `Foo` temporary to be dropped.
In this process, we also collect values that are borrowed. The reason is that the MIR transform for generators conservatively assumes anything borrowed is live across a suspend point (see `rustc_mir_transform::generator::locals_live_across_suspend_points`). We match this behavior here as well.
## 2. Gather drop events, reinitialization events, and control flow graph
After finding the values of interest, we perform a post-order traversal over the HIR tree to find the points where these values are dropped or reinitialized. We use the post-order index of each event because this is how the existing generator interior analysis refers to the position of suspend points and the scopes of variables.
During this traversal, we also record branching and merging information to handle control flow constructs such as `if`, `match`, and `loop`. This is necessary because values may be dropped along some control flow paths but not others.
## 3. Iterate to fixed point
The previous pass found the interesting events and locations, but now we need to find the actual ranges where things are dropped. Upon entry, we have a list of nodes ordered by their position in the post-order traversal. Each node has a set of successors. For each node we additionally keep a bitfield with one bit per potentially consumed value. The bit is set if we the value is dropped along all paths entering this node.
To compute the drop information, we first reverse the successor edges to find each node's predecessors. Then we iterate through each node, and for each node we set its dropped value bitfield to the intersection of all incoming dropped value bitfields.
If any bitfield for any node changes, we re-run the propagation loop again.
## 4. Ignore dropped values across suspend points
At this point we have a data structure where we can ask whether a value is guaranteed to be dropped at any post order index for the HIR tree. We use this information in `InteriorVisitor` to check whether a value in question is dropped at a particular suspend point. If it is, we do not include that value's type in the generator type.
Note that we had to augment the region scope tree to include all yields in scope, rather than just the last one as we did before.
r? `@nikomatsakis`
Pretty printer algorithm revamp step 2
This PR follows #92923 as a second chunk of modernizations backported from https://github.com/dtolnay/prettyplease into rustc_ast_pretty.
I've broken this up into atomic commits that hopefully are sensible in isolation. At every commit, the pretty printer is compilable and has runtime behavior that is identical to before and after the PR. None of the refactoring so far changes behavior.
The general theme of this chunk of commits is: the logic in the old pretty printer is doing some very basic things (pushing and popping tokens on a ring buffer) but expressed in a too-low-level way that I found makes it quite complicated/subtle to reason about. There are a number of obvious invariants that are "almost true" -- things like `self.left == self.buf.offset` and `self.right == self.buf.offset + self.buf.data.len()` and `self.right_total == self.left_total + self.buf.data.sum()`. The reason these things are "almost true" is the implementation tends to put updating one side of the invariant unreasonably far apart from updating the other side, leaving the invariant broken while unrelated stuff happens in between. The following code from master is an example of this:
e5e2b0be26/compiler/rustc_ast_pretty/src/pp.rs (L314-L317)
In this code the `advance_right` is reserving an entry into which to write a next token on the right side of the ring buffer, the `check_stack` is doing something totally unrelated to the right boundary of the ring buffer, and the `scan_push` is actually writing the token we previously reserved space for. Much of what this PR is doing is rearranging code to shrink the amount of stuff in between when an invariant is broken to when it is restored, until the whole thing can be factored out into one indivisible method call on the RingBuffer type.
The end state of the PR is that we can entirely eliminate `self.left` (because it's now just equal to `self.buf.offset` always) and `self.right` (because it's equal to `self.buf.offset + self.buf.data.len()` always) and the whole `Token::Eof` state which used to be the value of tokens that have been reserved space for but not yet written.
I found without these changes the pretty printer implementation to be hard to reason about and I wasn't able to confidently introduce improvements like trailing commas in `prettyplease` until after this refactor. The logic here is 43 years old at this point (Graydon translated it as directly as possible from the 1979 pretty printing paper) and while there are advantages to following the paper as closely as possible, in `prettyplease` I decided if we're going to adapt the algorithm to work better for Rust syntax, it was worthwhile making it easier to follow than the original.
mangling_v0: Skip extern blocks during mangling
There's no need to include the dummy `Nt` into the symbol name, items in extern blocks belong to their parent modules for all purposes except for inheriting the ABI and attributes.
Follow up to https://github.com/rust-lang/rust/pull/92032
(There's also a drive-by fix to the `rust-demangler` tool's tests, which don't run on CI, I initially attempted using them for testing this PR.)
Remove some unused ordering derivations based on `DefId`
Like #93018, this removes some unused/unneeded ordering derivations as part of ongoing work on #90317. Here, these changes are aimed at making https://github.com/rust-lang/rust/pull/90749 easier to review, test, and merge.
r? `@cjgillot`
Move expr- and item-related pretty printing functions to modules
Currently *compiler/rustc_ast_pretty/src/pprust/state.rs* is 2976 lines on master. The `tidy` limit is 3000, which is blocking #92243.
This PR adds a `mod expr;` and `mod item;` to move logic related to those AST nodes out of the single huge file.
Use iterator instead of recursion in `codegen_place`
This PR fixes the FIXME in `codegen_place` about using iterator instead of recursion when processing the `projection` field in `mir::PlaceRef`. At the same time, it also reduces the right drift.
Formally implement let chains
## Let chains
My longest and hardest contribution since #64010.
Thanks to `@Centril` for creating the RFC and special thanks to `@matthewjasper` for helping me since the beginning of this journey. In fact, `@matthewjasper` did much of the complicated MIR stuff so it's true to say that this feature wouldn't be possible without him. Thanks again `@matthewjasper!`
With the changes proposed in this PR, it will be possible to chain let expressions along side local variable declarations or ordinary conditional expressions. In other words, do much of what the `if_chain` crate already does.
## Other considerations
* `if let guard` and `let ... else` features need special care and should be handled in a following PR.
* Irrefutable patterns are allowed within a let chain context
* ~~Three Clippy lints were already converted to start dogfooding and help detect possible corner cases~~
cc #53667
We previously weren't tracking partial re-inits while being too
aggressive around partial drops. With this change, we simply ignore
partial drops, which is the safer, more conservative choice.
This changes drop range analysis to handle uninhabited return types such
as `!`. Since these calls to these functions do not return, we model
them as ending in an infinite loop.
This reduces the amount of work done, especially in later iterations,
by only processing nodes whose predecessors changed in the previous
iteration, or earlier in the current iteration. This also has the side
effect of completely ignoring all unreachable nodes.
The refactoring mainly keeps the separation between the modules clearer.
For example, process_deferred_edges function moved to cfg_build.rs since
that is really part of building the CFG, not finding the fixpoint.
Also, we use PostOrderId instead of usize in a lot more places now.
Splits drop_ranges into drop_ranges::record_consumed_borrow,
drop_ranges::cfg_build, and drop_ranges::cfg_propagate. The top level
drop_ranges module has an entry point that does all the coordination of
the other three phases, using code original in generator_interior.
