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rustc_errors: let DiagnosticBuilder::emit return a "guarantee of emission".

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Eduard-Mihai Burtescu 2022-01-27 09:44:25 +00:00
parent 0b9d70cf6d
commit b7e95dee65
83 changed files with 842 additions and 471 deletions
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234
compiler/rustc_errors/src/diagnostic_builder.rs
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@ -1,9 +1,10 @@
use crate::{Diagnostic, DiagnosticId, DiagnosticStyledString};
use crate::{Diagnostic, DiagnosticId, DiagnosticStyledString, ErrorReported};
use crate::{Handler, Level, StashKey};
use rustc_lint_defs::Applicability;
use rustc_span::{MultiSpan, Span};
use std::fmt::{self, Debug};
use std::marker::PhantomData;
use std::ops::{Deref, DerefMut};
use std::thread::panicking;
use tracing::debug;
@ -15,7 +16,24 @@ use tracing::debug;
/// extending `HandlerFlags`, accessed via `self.handler.flags`.
#[must_use]
#[derive(Clone)]
pub struct DiagnosticBuilder<'a> {
pub struct DiagnosticBuilder<'a, G: EmissionGuarantee> {
inner: DiagnosticBuilderInner<'a>,
_marker: PhantomData<G>,
}
/// This type exists only for `DiagnosticBuilder::forget_guarantee`, because it:
/// 1. lacks the `G` parameter and therefore `DiagnosticBuilder<G1>` can be
/// converted into `DiagnosticBuilder<G2>` while reusing the `inner` field
/// 2. can implement the `Drop` "bomb" instead of `DiagnosticBuilder`, as it
/// contains all of the data (`state` + `diagnostic`) of `DiagnosticBuilder`
///
/// The `diagnostic` field is not `Copy` and can't be moved out of whichever
/// type implements the `Drop` "bomb", but because of the above two facts, that
/// never needs to happen - instead, the whole `inner: DiagnosticBuilderInner`
/// can be moved out of a `DiagnosticBuilder` and into another.
#[must_use]
#[derive(Clone)]
struct DiagnosticBuilderInner<'a> {
state: DiagnosticBuilderState<'a>,
/// `Diagnostic` is a large type, and `DiagnosticBuilder` is often used as a
@ -38,8 +56,8 @@ enum DiagnosticBuilderState<'a> {
/// assumed that `.emit()` was previously called, to end up in this state.
///
/// While this is also used by `.cancel()`, this state is only observed by
/// the `Drop` `impl` of `DiagnosticBuilder`, as `.cancel()` takes `self`
/// by-value specifically to prevent any attempts to `.emit()`.
/// the `Drop` `impl` of `DiagnosticBuilderInner`, as `.cancel()` takes
/// `self` by-value specifically to prevent any attempts to `.emit()`.
///
// FIXME(eddyb) currently this doesn't prevent extending the `Diagnostic`,
// despite that being potentially lossy, if important information is added
@ -53,6 +71,133 @@ rustc_data_structures::static_assert_size!(
std::mem::size_of::<&Handler>()
);
/// Trait for types that `DiagnosticBuilder::emit` can return as a "guarantee"
/// (or "proof") token that the emission happened.
pub trait EmissionGuarantee: Sized {
/// Implementation of `DiagnosticBuilder::emit`, fully controlled by each
/// `impl` of `EmissionGuarantee`, to make it impossible to create a value
/// of `Self` without actually performing the emission.
#[track_caller]
fn diagnostic_builder_emit_producing_guarantee(db: &mut DiagnosticBuilder<'_, Self>) -> Self;
}
/// Private module for sealing the `IsError` helper trait.
mod sealed_level_is_error {
use crate::Level;
/// Sealed helper trait for statically checking that a `Level` is an error.
crate trait IsError<const L: Level> {}
impl IsError<{ Level::Bug }> for () {}
impl IsError<{ Level::DelayedBug }> for () {}
impl IsError<{ Level::Fatal }> for () {}
// NOTE(eddyb) `Level::Error { lint: true }` is also an error, but lints
// don't need error guarantees, as their levels are always dynamic.
impl IsError<{ Level::Error { lint: false } }> for () {}
}
impl<'a> DiagnosticBuilder<'a, ErrorReported> {
/// Convenience function for internal use, clients should use one of the
/// `struct_*` methods on [`Handler`].
crate fn new_guaranteeing_error<const L: Level>(handler: &'a Handler, message: &str) -> Self
where
(): sealed_level_is_error::IsError<L>,
{
Self {
inner: DiagnosticBuilderInner {
state: DiagnosticBuilderState::Emittable(handler),
diagnostic: Box::new(Diagnostic::new_with_code(L, None, message)),
},
_marker: PhantomData,
}
}
/// Discard the guarantee `.emit()` would return, in favor of having the
/// type `DiagnosticBuilder<'a, ()>`. This may be necessary whenever there
/// is a common codepath handling both errors and warnings.
pub fn forget_guarantee(self) -> DiagnosticBuilder<'a, ()> {
DiagnosticBuilder { inner: self.inner, _marker: PhantomData }
}
}
// FIXME(eddyb) make `ErrorReported` impossible to create outside `.emit()`.
impl EmissionGuarantee for ErrorReported {
fn diagnostic_builder_emit_producing_guarantee(db: &mut DiagnosticBuilder<'_, Self>) -> Self {
match db.inner.state {
// First `.emit()` call, the `&Handler` is still available.
DiagnosticBuilderState::Emittable(handler) => {
db.inner.state = DiagnosticBuilderState::AlreadyEmittedOrDuringCancellation;
handler.emit_diagnostic(&db.inner.diagnostic);
// Only allow a guarantee if the `level` wasn't switched to a
// non-error - the field isn't `pub`, but the whole `Diagnostic`
// can be overwritten with a new one, thanks to `DerefMut`.
assert!(
db.inner.diagnostic.is_error(),
"emitted non-error ({:?}) diagnostic \
from `DiagnosticBuilder<ErrorReported>`",
db.inner.diagnostic.level,
);
ErrorReported
}
// `.emit()` was previously called, disallowed from repeating it,
// but can take advantage of the previous `.emit()`'s guarantee
// still being applicable (i.e. as a form of idempotency).
DiagnosticBuilderState::AlreadyEmittedOrDuringCancellation => {
// Only allow a guarantee if the `level` wasn't switched to a
// non-error - the field isn't `pub`, but the whole `Diagnostic`
// can be overwritten with a new one, thanks to `DerefMut`.
assert!(
db.inner.diagnostic.is_error(),
"`DiagnosticBuilder<ErrorReported>`'s diagnostic \
became non-error ({:?}), after original `.emit()`",
db.inner.diagnostic.level,
);
ErrorReported
}
}
}
}
impl<'a> DiagnosticBuilder<'a, ()> {
/// Convenience function for internal use, clients should use one of the
/// `struct_*` methods on [`Handler`].
crate fn new(handler: &'a Handler, level: Level, message: &str) -> Self {
let diagnostic = Diagnostic::new_with_code(level, None, message);
Self::new_diagnostic(handler, diagnostic)
}
/// Creates a new `DiagnosticBuilder` with an already constructed
/// diagnostic.
crate fn new_diagnostic(handler: &'a Handler, diagnostic: Diagnostic) -> Self {
debug!("Created new diagnostic");
Self {
inner: DiagnosticBuilderInner {
state: DiagnosticBuilderState::Emittable(handler),
diagnostic: Box::new(diagnostic),
},
_marker: PhantomData,
}
}
}
// FIXME(eddyb) should there be a `Option<ErrorReported>` impl as well?
impl EmissionGuarantee for () {
fn diagnostic_builder_emit_producing_guarantee(db: &mut DiagnosticBuilder<'_, Self>) -> Self {
match db.inner.state {
// First `.emit()` call, the `&Handler` is still available.
DiagnosticBuilderState::Emittable(handler) => {
db.inner.state = DiagnosticBuilderState::AlreadyEmittedOrDuringCancellation;
handler.emit_diagnostic(&db.inner.diagnostic);
}
// `.emit()` was previously called, disallowed from repeating it.
DiagnosticBuilderState::AlreadyEmittedOrDuringCancellation => {}
}
}
}
/// In general, the `DiagnosticBuilder` uses deref to allow access to
/// the fields and methods of the embedded `diagnostic` in a
/// transparent way. *However,* many of the methods are intended to
@ -83,52 +228,43 @@ macro_rules! forward {
$(#[$attrs])*
#[doc = concat!("See [`Diagnostic::", stringify!($n), "()`].")]
pub fn $n(&mut self, $($name: $ty),*) -> &mut Self {
self.diagnostic.$n($($name),*);
self.inner.diagnostic.$n($($name),*);
self
}
};
}
impl<'a> Deref for DiagnosticBuilder<'a> {
impl<G: EmissionGuarantee> Deref for DiagnosticBuilder<'_, G> {
type Target = Diagnostic;
fn deref(&self) -> &Diagnostic {
&self.diagnostic
&self.inner.diagnostic
}
}
impl<'a> DerefMut for DiagnosticBuilder<'a> {
impl<G: EmissionGuarantee> DerefMut for DiagnosticBuilder<'_, G> {
fn deref_mut(&mut self) -> &mut Diagnostic {
&mut self.diagnostic
&mut self.inner.diagnostic
}
}
impl<'a> DiagnosticBuilder<'a> {
impl<'a, G: EmissionGuarantee> DiagnosticBuilder<'a, G> {
/// Emit the diagnostic.
pub fn emit(&mut self) {
match self.state {
// First `.emit()` call, the `&Handler` is still available.
DiagnosticBuilderState::Emittable(handler) => {
handler.emit_diagnostic(&self);
self.state = DiagnosticBuilderState::AlreadyEmittedOrDuringCancellation;
}
// `.emit()` was previously called, disallowed from repeating it.
DiagnosticBuilderState::AlreadyEmittedOrDuringCancellation => {
// FIXME(eddyb) rely on this to return a "proof" that an error
// was/will be emitted, despite doing no emission *here and now*.
}
}
#[track_caller]
pub fn emit(&mut self) -> G {
G::diagnostic_builder_emit_producing_guarantee(self)
}
/// Emit the diagnostic unless `delay` is true,
/// in which case the emission will be delayed as a bug.
///
/// See `emit` and `delay_as_bug` for details.
pub fn emit_unless(&mut self, delay: bool) {
#[track_caller]
pub fn emit_unless(&mut self, delay: bool) -> G {
if delay {
self.downgrade_to_delayed_bug();
}
self.emit();
self.emit()
}
/// Cancel the diagnostic (a structured diagnostic must either be emitted or
@ -138,7 +274,7 @@ impl<'a> DiagnosticBuilder<'a> {
/// which may be expected to *guarantee* the emission of an error, either
/// at the time of the call, or through a prior `.emit()` call.
pub fn cancel(mut self) {
self.state = DiagnosticBuilderState::AlreadyEmittedOrDuringCancellation;
self.inner.state = DiagnosticBuilderState::AlreadyEmittedOrDuringCancellation;
drop(self);
}
@ -156,7 +292,7 @@ impl<'a> DiagnosticBuilder<'a> {
/// Converts the builder to a `Diagnostic` for later emission,
/// unless handler has disabled such buffering, or `.emit()` was called.
pub fn into_diagnostic(mut self) -> Option<(Diagnostic, &'a Handler)> {
let handler = match self.state {
let handler = match self.inner.state {
// No `.emit()` calls, the `&Handler` is still available.
DiagnosticBuilderState::Emittable(handler) => handler,
// `.emit()` was previously called, nothing we can do.
@ -172,7 +308,7 @@ impl<'a> DiagnosticBuilder<'a> {
// Take the `Diagnostic` by replacing it with a dummy.
let dummy = Diagnostic::new(Level::Allow, "");
let diagnostic = std::mem::replace(&mut *self.diagnostic, dummy);
let diagnostic = std::mem::replace(&mut *self.inner.diagnostic, dummy);
// Disable the ICE on `Drop`.
self.cancel();
@ -347,57 +483,27 @@ impl<'a> DiagnosticBuilder<'a> {
forward!(pub fn set_primary_message(&mut self, msg: impl Into<String>) -> &mut Self);
forward!(pub fn set_span(&mut self, sp: impl Into<MultiSpan>) -> &mut Self);
forward!(pub fn code(&mut self, s: DiagnosticId) -> &mut Self);
/// Convenience function for internal use, clients should use one of the
/// `struct_*` methods on [`Handler`].
crate fn new(handler: &'a Handler, level: Level, message: &str) -> DiagnosticBuilder<'a> {
DiagnosticBuilder::new_with_code(handler, level, None, message)
}
/// Convenience function for internal use, clients should use one of the
/// `struct_*` methods on [`Handler`].
crate fn new_with_code(
handler: &'a Handler,
level: Level,
code: Option<DiagnosticId>,
message: &str,
) -> DiagnosticBuilder<'a> {
let diagnostic = Diagnostic::new_with_code(level, code, message);
DiagnosticBuilder::new_diagnostic(handler, diagnostic)
}
/// Creates a new `DiagnosticBuilder` with an already constructed
/// diagnostic.
crate fn new_diagnostic(handler: &'a Handler, diagnostic: Diagnostic) -> DiagnosticBuilder<'a> {
debug!("Created new diagnostic");
DiagnosticBuilder {
state: DiagnosticBuilderState::Emittable(handler),
diagnostic: Box::new(diagnostic),
}
}
}
impl<'a> Debug for DiagnosticBuilder<'a> {
impl<G: EmissionGuarantee> Debug for DiagnosticBuilder<'_, G> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
self.diagnostic.fmt(f)
self.inner.diagnostic.fmt(f)
}
}
/// Destructor bomb - a `DiagnosticBuilder` must be either emitted or cancelled
/// or we emit a bug.
impl<'a> Drop for DiagnosticBuilder<'a> {
impl Drop for DiagnosticBuilderInner<'_> {
fn drop(&mut self) {
match self.state {
// No `.emit()` or `.cancel()` calls.
DiagnosticBuilderState::Emittable(handler) => {
if !panicking() {
let mut db = DiagnosticBuilder::new(
handler,
handler.emit_diagnostic(&Diagnostic::new(
Level::Bug,
"the following error was constructed but not emitted",
);
db.emit();
handler.emit_diagnostic(&self);
));
handler.emit_diagnostic(&self.diagnostic);
panic!();
}
}