Merge pull request rust-lang#2803 from rust-lang/tshepang/sembr

sembr a few files

Author: tshepang

src/doc/rustc-dev-guide/ci/sembr/src/main.rs

@@ -15,7 +15,7 @@ struct Cli {
     /// Modify files that do not comply
     overwrite: bool,
     /// Applies to lines that are to be split
-    #[arg(long, default_value_t = 100)]
+    #[arg(long, default_value_t = 80)]
     line_length_limit: usize,
 }
 

src/doc/rustc-dev-guide/src/borrow-check/region-inference/member-constraints.md

@@ -1,17 +1,18 @@
 # Member constraints
 
 A member constraint `'m member of ['c_1..'c_N]` expresses that the
-region `'m` must be *equal* to some **choice regions** `'c_i` (for
-some `i`). These constraints cannot be expressed by users, but they
-arise from `impl Trait` due to its lifetime capture rules. Consider a
-function such as the following:
+region `'m` must be *equal* to some **choice regions** `'c_i` (for some `i`).
+These constraints cannot be expressed by users, but they
+arise from `impl Trait` due to its lifetime capture rules.
+Consider a function such as the following:
 
 ```rust,ignore
 fn make(a: &'a u32, b: &'b u32) -> impl Trait<'a, 'b> { .. }
 ```
 
 Here, the true return type (often called the "hidden type") is only
-permitted to capture the lifetimes `'a` or `'b`. You can kind of see
+permitted to capture the lifetimes `'a` or `'b`.
+You can kind of see
 this more clearly by desugaring that `impl Trait` return type into its
 more explicit form:
 
@@ -23,16 +24,17 @@ fn make(a: &'a u32, b: &'b u32) -> MakeReturn<'a, 'b> { .. }
 Here, the idea is that the hidden type must be some type that could
 have been written in place of the `impl Trait<'x, 'y>` -- but clearly
 such a type can only reference the regions `'x` or `'y` (or
-`'static`!), as those are the only names in scope. This limitation is
+`'static`!), as those are the only names in scope.
+This limitation is
 then translated into a restriction to only access `'a` or `'b` because
 we are returning `MakeReturn<'a, 'b>`, where `'x` and `'y` have been
 replaced with `'a` and `'b` respectively.
 
 ## Detailed example
 
 To help us explain member constraints in more detail, let's spell out
-the `make` example in a bit more detail. First off, let's assume that
-you have some dummy trait:
+the `make` example in a bit more detail.
+First off, let's assume that you have some dummy trait:
 
 ```rust,ignore
 trait Trait<'a, 'b> { }
@@ -49,8 +51,8 @@ fn make(a: &'a u32, b: &'b u32) -> MakeReturn<'a, 'b> {
 ```
 
 What happens in this case is that the return type will be `(&'0 u32, &'1 u32)`,
-where `'0` and `'1` are fresh region variables. We will have the following
-region constraints:
+where `'0` and `'1` are fresh region variables.
+We will have the following region constraints:
 
 ```txt
 '0 live at {L}
@@ -67,11 +69,11 @@ return tuple is constructed to where it is returned (in fact, `'0` and
 `'1` might have slightly different liveness sets, but that's not very
 interesting to the point we are illustrating here).
 
-The `'a: '0` and `'b: '1` constraints arise from subtyping. When we
-construct the `(a, b)` value, it will be assigned type `(&'0 u32, &'1
+The `'a: '0` and `'b: '1` constraints arise from subtyping.
+When we construct the `(a, b)` value, it will be assigned type `(&'0 u32, &'1
 u32)` -- the region variables reflect that the lifetimes of these
-references could be made smaller. For this value to be created from
-`a` and `b`, however, we do require that:
+references could be made smaller.
+For this value to be created from `a` and `b`, however, we do require that:
 
 ```txt
 (&'a u32, &'b u32) <: (&'0 u32, &'1 u32)
@@ -82,35 +84,39 @@ which means in turn that `&'a u32 <: &'0 u32` and hence that `'a: '0`
 
 Note that if we ignore member constraints, the value of `'0` would be
 inferred to some subset of the function body (from the liveness
-constraints, which we did not write explicitly). It would never become
+constraints, which we did not write explicitly).
+It would never become
 `'a`, because there is no need for it too -- we have a constraint that
-`'a: '0`, but that just puts a "cap" on how *large* `'0` can grow to
-become. Since we compute the *minimal* value that we can, we are happy
-to leave `'0` as being just equal to the liveness set. This is where
-member constraints come in.
+`'a: '0`, but that just puts a "cap" on how *large* `'0` can grow to become.
+Since we compute the *minimal* value that we can, we are happy
+to leave `'0` as being just equal to the liveness set.
+This is where member constraints come in.
 
 ## Choices are always lifetime parameters
 
 At present, the "choice" regions from a member constraint are always lifetime
 parameters from the current function. As of <!-- date-check --> March 2026,
 this falls out from the placement of impl Trait, though in the future it may not
-be the case. We take some advantage of this fact, as it simplifies the current
-code. In particular, we don't have to consider a case like `'0 member of ['1,
+be the case.
+We take some advantage of this fact, as it simplifies the current code.
+In particular, we don't have to consider a case like `'0 member of ['1,
 'static]`, in which the value of both `'0` and `'1` are being inferred and hence
-changing. See [rust-lang/rust#61773][#61773] for more information.
+changing.
+See [rust-lang/rust#61773][#61773] for more information.
 
 [#61773]: https://github.com/rust-lang/rust/issues/61773
 
 ## Applying member constraints
 
-Member constraints are a bit more complex than other forms of
-constraints. This is because they have a "or" quality to them -- that
+Member constraints are a bit more complex than other forms of constraints.
+This is because they have a "or" quality to them -- that
 is, they describe multiple choices that we must select from. E.g., in
 our example constraint `'0 member of ['a, 'b, 'static]`, it might be
-that `'0` is equal to `'a`, `'b`, *or* `'static`. How can we pick the
-correct one?  What we currently do is to look for a *minimal choice*
--- if we find one, then we will grow `'0` to be equal to that minimal
-choice. To find that minimal choice, we take two factors into
+that `'0` is equal to `'a`, `'b`, *or* `'static`.
+How can we pick the correct one?
+What we currently do is to look for a *minimal choice*
+-- if we find one, then we will grow `'0` to be equal to that minimal choice.
+To find that minimal choice, we take two factors into
 consideration: lower and upper bounds.
 
 ### Lower bounds
@@ -121,30 +127,34 @@ apply member constraints, we've already *computed* the lower bounds of
 `'0` because we computed its minimal value (or at least, the lower
 bounds considering everything but member constraints).
 
-Let `LB` be the current value of `'0`. We know then that `'0: LB` must
-hold, whatever the final value of `'0` is. Therefore, we can rule out
+Let `LB` be the current value of `'0`.
+We know then that `'0: LB` must hold, whatever the final value of `'0` is.
+Therefore, we can rule out
 any choice `'choice` where `'choice: LB` does not hold.
 
-Unfortunately, in our example, this is not very helpful. The lower
-bound for `'0` will just be the liveness set `{L}`, and we know that
-all the lifetime parameters outlive that set. So we are left with the
-same set of choices here. (But in other examples, particularly those
+Unfortunately, in our example, this is not very helpful.
+The lower bound for `'0` will just be the liveness set `{L}`, and we know that
+all the lifetime parameters outlive that set.
+So we are left with the same set of choices here.
+(But in other examples, particularly those
 with different variance, lower bound constraints may be relevant.)
 
 ### Upper bounds
 
 The *upper bounds* are those lifetimes that *must outlive* `'0` --
 i.e., that `'0` must be *smaller* than. In our example, this would be
-`'a`, because we have the constraint that `'a: '0`. In more complex
-examples, the chain may be more indirect.
+`'a`, because we have the constraint that `'a: '0`.
+In more complex examples, the chain may be more indirect.
 
 We can use upper bounds to rule out members in a very similar way to
-lower bounds. If UB is some upper bound, then we know that `UB:
+lower bounds.
+If UB is some upper bound, then we know that `UB:
 '0` must hold, so we can rule out any choice `'choice` where `UB:
 'choice` does not hold.
 
 In our example, we would be able to reduce our choice set from `['a,
-'b, 'static]` to just `['a]`. This is because `'0` has an upper bound
+'b, 'static]` to just `['a]`.
+This is because `'0` has an upper bound
 of `'a`, and neither `'a: 'b` nor `'a: 'static` is known to hold.
 
 (For notes on how we collect upper bounds in the implementation, see
@@ -153,39 +163,45 @@ of `'a`, and neither `'a: 'b` nor `'a: 'static` is known to hold.
 ### Minimal choice
 
 After applying lower and upper bounds, we can still sometimes have
-multiple possibilities. For example, imagine a variant of our example
-using types with the opposite variance. In that case, we would have
-the constraint `'0: 'a` instead of `'a: '0`. Hence the current value
-of `'0` would be `{L, 'a}`. Using this as a lower bound, we would be
+multiple possibilities.
+For example, imagine a variant of our example
+using types with the opposite variance.
+In that case, we would have the constraint `'0: 'a` instead of `'a: '0`.
+Hence the current value of `'0` would be `{L, 'a}`.
+Using this as a lower bound, we would be
 able to narrow down the member choices to `['a, 'static]` because `'b:
-'a` is not known to hold (but `'a: 'a` and `'static: 'a` do hold). We
-would not have any upper bounds, so that would be our final set of choices.
+'a` is not known to hold (but `'a: 'a` and `'static: 'a` do hold).
+We would not have any upper bounds, so that would be our final set of choices.
 
 In that case, we apply the **minimal choice** rule -- basically, if
-one of our choices if smaller than the others, we can use that. In
-this case, we would opt for `'a` (and not `'static`).
+one of our choices if smaller than the others, we can use that.
+In this case, we would opt for `'a` (and not `'static`).
 
 This choice is consistent with the general 'flow' of region
 propagation, which always aims to compute a minimal value for the
-region being inferred. However, it is somewhat arbitrary.
+region being inferred.
+However, it is somewhat arbitrary.
 
 <a id="collecting"></a>
 
 ### Collecting upper bounds in the implementation
 
 In practice, computing upper bounds is a bit inconvenient, because our
-data structures are setup for the opposite. What we do is to compute
+data structures are setup for the opposite.
+What we do is to compute
 the **reverse SCC graph** (we do this lazily and cache the result) --
-that is, a graph where `'a: 'b` induces an edge `SCC('b) ->
-SCC('a)`. Like the normal SCC graph, this is a DAG. We can then do a
-depth-first search starting from `SCC('0)` in this graph. This will
-take us to all the SCCs that must outlive `'0`.
+that is, a graph where `'a: 'b` induces an edge `SCC('b) -> SCC('a)`.
+Like the normal SCC graph, this is a DAG.
+We can then do a depth-first search starting from `SCC('0)` in this graph.
+This will take us to all the SCCs that must outlive `'0`.
 
 One wrinkle is that, as we walk the "upper bound" SCCs, their values
-will not yet have been fully computed. However, we **have** already
+will not yet have been fully computed.
+However, we **have** already
 applied their liveness constraints, so we have some information about
-their value. In particular, for any regions representing lifetime
+their value.
+In particular, for any regions representing lifetime
 parameters, their value will contain themselves (i.e., the initial
-value for `'a` includes `'a` and the value for `'b` contains `'b`). So
-we can collect all of the lifetime parameters that are reachable,
+value for `'a` includes `'a` and the value for `'b` contains `'b`).
+So we can collect all of the lifetime parameters that are reachable,
 which is precisely what we are interested in.

src/doc/rustc-dev-guide/src/diagnostics/lintstore.md

@@ -3,15 +3,14 @@
 This page documents some of the machinery around lint registration and how we
 run lints in the compiler.
 
-The [`LintStore`] is the central piece of infrastructure, around which
-everything rotates. The `LintStore` is held as part of the [`Session`], and it
+The [`LintStore`] is the central piece of infrastructure, around which everything rotates.
+The `LintStore` is held as part of the [`Session`], and it
 gets populated with the list of lints shortly after the `Session` is created.
 
 ## Lints vs. lint passes
 
-There are two parts to the linting mechanism within the compiler: lints and
-lint passes. Unfortunately, a lot of the documentation we have refers to both
-of these as just "lints."
+There are two parts to the linting mechanism within the compiler: lints and lint passes.
+Unfortunately, a lot of the documentation we have refers to both of these as just "lints."
 
 First, we have the lint declarations themselves,
 and this is where the name and default lint level and other metadata come from.
@@ -24,10 +23,11 @@ like all macros).
 we lint against direct declarations without the use of the macro.
 
 Lint declarations don't carry any "state" - they are merely global identifiers
-and descriptions of lints. We assert at runtime that they are not registered
-twice (by lint name).
+and descriptions of lints.
+We assert at runtime that they are not registered twice (by lint name).
 
-Lint passes are the meat of any lint. Notably, there is not a one-to-one
+Lint passes are the meat of any lint.
+Notably, there is not a one-to-one
 relationship between lints and lint passes; a lint might not have any lint pass
 that emits it, it could have many, or just one -- the compiler doesn't track
 whether a pass is in any way associated with a particular lint, and frequently
@@ -44,36 +44,33 @@ and all lints are registered.
 There are three 'sources' of lints:
 
 * internal lints: lints only used by the rustc codebase
-* builtin lints: lints built into the compiler and not provided by some outside
-  source
-* `rustc_interface::Config`[`register_lints`]: lints passed into the compiler
-  during construction
+* builtin lints: lints built into the compiler and not provided by some outside source
+* `rustc_interface::Config`[`register_lints`]: lints passed into the compiler during construction
 
-Lints are registered via the [`LintStore::register_lint`] function. This should
-happen just once for any lint, or an ICE will occur.
+Lints are registered via the [`LintStore::register_lint`] function.
+This should happen just once for any lint, or an ICE will occur.
 
-Once the registration is complete, we "freeze" the lint store by placing it in
-an `Arc`.
+Once the registration is complete, we "freeze" the lint store by placing it in an `Arc`.
 
 Lint passes are registered separately into one of the categories
-(pre-expansion, early, late, late module). Passes are registered as a closure
+(pre-expansion, early, late, late module).
+Passes are registered as a closure
 -- i.e., `impl Fn() -> Box<dyn X>`, where `dyn X` is either an early or late
-lint pass trait object. When we run the lint passes, we run the closure and
-then invoke the lint pass methods. The lint pass methods take `&mut self` so
-they can keep track of state internally.
+lint pass trait object.
+When we run the lint passes, we run the closure and then invoke the lint pass methods.
+The lint pass methods take `&mut self` so they can keep track of state internally.
 
 #### Internal lints
 
-These are lints used just by the compiler or drivers like `clippy`. They can be
-found in [`rustc_lint::internal`].
+These are lints used just by the compiler or drivers like `clippy`.
+They can be found in [`rustc_lint::internal`].
 
 An example of such a lint is the check that lint passes are implemented using
-the `declare_lint_pass!` macro and not by hand. This is accomplished with the
-`LINT_PASS_IMPL_WITHOUT_MACRO` lint.
+the `declare_lint_pass!` macro and not by hand.
+This is accomplished with the `LINT_PASS_IMPL_WITHOUT_MACRO` lint.
 
 Registration of these lints happens in the [`rustc_lint::register_internals`]
-function which is called when constructing a new lint store inside
-[`rustc_lint::new_lint_store`].
+function which is called when constructing a new lint store inside [`rustc_lint::new_lint_store`].
 
 #### Builtin Lints
 
@@ -83,19 +80,18 @@ Often the first provides the definitions for the lints themselves,
 and the latter provides the lint pass definitions (and implementations),
 but this is not always true.
 
-The builtin lint registration happens in
-the [`rustc_lint::register_builtins`] function.
+The builtin lint registration happens in the [`rustc_lint::register_builtins`] function.
 Just like with internal lints,
 this happens inside of [`rustc_lint::new_lint_store`].
 
 #### Driver lints
 
 These are the lints provided by drivers via the `rustc_interface::Config`
-[`register_lints`] field, which is a callback. Drivers should, if finding it
-already set, call the function currently set within the callback they add. The
-best way for drivers to get access to this is by overriding the
-`Callbacks::config` function which gives them direct access to the `Config`
-structure.
+[`register_lints`] field, which is a callback.
+Drivers should, if finding it
+already set, call the function currently set within the callback they add.
+The best way for drivers to get access to this is by overriding the
+`Callbacks::config` function which gives them direct access to the `Config` structure.
 
 ## Compiler lint passes are combined into one pass
 
@@ -105,8 +101,8 @@ of lint passes. Instead, we have a single lint pass of each variety (e.g.,
 individual lint passes; this is because then we get the benefits of static over
 dynamic dispatch for each of the (often empty) trait methods.
 
-Ideally, we'd not have to do this, since it adds to the complexity of
-understanding the code. However, with the current type-erased lint store
+Ideally, we'd not have to do this, since it adds to the complexity of understanding the code.
+However, with the current type-erased lint store
 approach, it is beneficial to do so for performance reasons.
 
 [`LintStore`]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_lint/struct.LintStore.html