From 267df7a54675fdbef25bd2a5f24e66ee381b0844 Mon Sep 17 00:00:00 2001 From: Nadrieril Date: Thu, 18 Jan 2024 16:16:30 +0100 Subject: [PATCH] Never pattern in function arguments diverges --- compiler/rustc_hir_typeck/src/check.rs | 10 +++- compiler/rustc_hir_typeck/src/expr.rs | 9 ++- compiler/rustc_hir_typeck/src/fn_ctxt/mod.rs | 9 +++ .../diverge-causes-unreachable-code.rs | 35 ++++++++++++ .../diverge-causes-unreachable-code.stderr | 38 +++++++++++++ .../rfc-0000-never_patterns/diverges-not.rs | 56 +++++++++++++++++++ .../diverges-not.stderr | 55 ++++++++++++++++++ .../rfcs/rfc-0000-never_patterns/diverges.rs | 29 ++++++++++ 8 files changed, 238 insertions(+), 3 deletions(-) create mode 100644 tests/ui/rfcs/rfc-0000-never_patterns/diverge-causes-unreachable-code.rs create mode 100644 tests/ui/rfcs/rfc-0000-never_patterns/diverge-causes-unreachable-code.stderr create mode 100644 tests/ui/rfcs/rfc-0000-never_patterns/diverges-not.rs create mode 100644 tests/ui/rfcs/rfc-0000-never_patterns/diverges-not.stderr create mode 100644 tests/ui/rfcs/rfc-0000-never_patterns/diverges.rs diff --git a/compiler/rustc_hir_typeck/src/check.rs b/compiler/rustc_hir_typeck/src/check.rs index c887368b2a233..4d9f5b831c161 100644 --- a/compiler/rustc_hir_typeck/src/check.rs +++ b/compiler/rustc_hir_typeck/src/check.rs @@ -2,8 +2,7 @@ use std::cell::RefCell; use crate::coercion::CoerceMany; use crate::gather_locals::GatherLocalsVisitor; -use crate::CoroutineTypes; -use crate::FnCtxt; +use crate::{CoroutineTypes, Diverges, FnCtxt}; use rustc_hir as hir; use rustc_hir::def::DefKind; use rustc_hir::intravisit::Visitor; @@ -76,6 +75,12 @@ pub(super) fn check_fn<'a, 'tcx>( let ty: Option<&hir::Ty<'_>> = try { inputs_hir?.get(idx)? }; let ty_span = ty.map(|ty| ty.span); fcx.check_pat_top(param.pat, param_ty, ty_span, None, None); + if param.pat.is_never_pattern() { + fcx.function_diverges_because_of_empty_arguments.set(Diverges::Always { + span: param.pat.span, + custom_note: Some("any code following a never pattern is unreachable"), + }); + } // Check that argument is Sized. if !params_can_be_unsized { @@ -105,6 +110,7 @@ pub(super) fn check_fn<'a, 'tcx>( hir::FnRetTy::Return(ty) => ty.span, }; fcx.require_type_is_sized(declared_ret_ty, return_or_body_span, traits::SizedReturnType); + fcx.is_whole_body.set(true); fcx.check_return_expr(body.value, false); // Finalize the return check by taking the LUB of the return types diff --git a/compiler/rustc_hir_typeck/src/expr.rs b/compiler/rustc_hir_typeck/src/expr.rs index 4b41834f0c47d..941defdfee5c8 100644 --- a/compiler/rustc_hir_typeck/src/expr.rs +++ b/compiler/rustc_hir_typeck/src/expr.rs @@ -220,9 +220,16 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> { self.warn_if_unreachable(expr.hir_id, expr.span, "expression"); } - // Hide the outer diverging and has_errors flags. + // Whether a past expression diverges doesn't affect typechecking of this expression, so we + // reset `diverges` while checking `expr`. let old_diverges = self.diverges.replace(Diverges::Maybe); + if self.is_whole_body.replace(false) { + // If this expression is the whole body and the function diverges because of its + // arguments, we check this here to ensure the body is considered to diverge. + self.diverges.set(self.function_diverges_because_of_empty_arguments.get()) + }; + let ty = ensure_sufficient_stack(|| match &expr.kind { hir::ExprKind::Path( qpath @ (hir::QPath::Resolved(..) | hir::QPath::TypeRelative(..)), diff --git a/compiler/rustc_hir_typeck/src/fn_ctxt/mod.rs b/compiler/rustc_hir_typeck/src/fn_ctxt/mod.rs index fde3d41faecf0..73d195b743471 100644 --- a/compiler/rustc_hir_typeck/src/fn_ctxt/mod.rs +++ b/compiler/rustc_hir_typeck/src/fn_ctxt/mod.rs @@ -103,6 +103,13 @@ pub struct FnCtxt<'a, 'tcx> { /// the diverges flag is set to something other than `Maybe`. pub(super) diverges: Cell, + /// If one of the function arguments is a never pattern, this counts as diverging code. We check + /// this while checking the function body. + pub(super) function_diverges_because_of_empty_arguments: Cell, + + /// Whether the currently checked node is the whole body of the function. + pub(super) is_whole_body: Cell, + pub(super) enclosing_breakables: RefCell>, pub(super) inh: &'a Inherited<'tcx>, @@ -124,6 +131,8 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> { ret_coercion_span: Cell::new(None), coroutine_types: None, diverges: Cell::new(Diverges::Maybe), + function_diverges_because_of_empty_arguments: Cell::new(Diverges::Maybe), + is_whole_body: Cell::new(false), enclosing_breakables: RefCell::new(EnclosingBreakables { stack: Vec::new(), by_id: Default::default(), diff --git a/tests/ui/rfcs/rfc-0000-never_patterns/diverge-causes-unreachable-code.rs b/tests/ui/rfcs/rfc-0000-never_patterns/diverge-causes-unreachable-code.rs new file mode 100644 index 0000000000000..5c852c8adcccf --- /dev/null +++ b/tests/ui/rfcs/rfc-0000-never_patterns/diverge-causes-unreachable-code.rs @@ -0,0 +1,35 @@ +#![feature(never_patterns)] +#![allow(incomplete_features)] +#![deny(unreachable_patterns)] +#![deny(unreachable_code)] + +fn main() {} + +enum Void {} + +fn never_arg(!: Void) -> u32 { + println!(); + //~^ ERROR unreachable statement +} + +fn ref_never_arg(&!: &Void) -> u32 { + println!(); + //~^ ERROR unreachable statement +} + +//fn never_let() -> u32 { +// let ptr: *const Void = std::ptr::null(); +// unsafe { +// let ! = *ptr; +// } +// println!(); +//} + +fn never_match() -> u32 { + let ptr: *const Void = std::ptr::null(); + unsafe { + match *ptr { ! }; + } + println!(); + //~^ ERROR unreachable statement +} diff --git a/tests/ui/rfcs/rfc-0000-never_patterns/diverge-causes-unreachable-code.stderr b/tests/ui/rfcs/rfc-0000-never_patterns/diverge-causes-unreachable-code.stderr new file mode 100644 index 0000000000000..c9cd3f53944e4 --- /dev/null +++ b/tests/ui/rfcs/rfc-0000-never_patterns/diverge-causes-unreachable-code.stderr @@ -0,0 +1,38 @@ +error: unreachable statement + --> $DIR/diverge-causes-unreachable-code.rs:11:5 + | +LL | fn never_arg(!: Void) -> u32 { + | - any code following a never pattern is unreachable +LL | println!(); + | ^^^^^^^^^^ unreachable statement + | +note: the lint level is defined here + --> $DIR/diverge-causes-unreachable-code.rs:4:9 + | +LL | #![deny(unreachable_code)] + | ^^^^^^^^^^^^^^^^ + = note: this error originates in the macro `$crate::print` which comes from the expansion of the macro `println` (in Nightly builds, run with -Z macro-backtrace for more info) + +error: unreachable statement + --> $DIR/diverge-causes-unreachable-code.rs:16:5 + | +LL | fn ref_never_arg(&!: &Void) -> u32 { + | -- any code following a never pattern is unreachable +LL | println!(); + | ^^^^^^^^^^ unreachable statement + | + = note: this error originates in the macro `$crate::print` which comes from the expansion of the macro `println` (in Nightly builds, run with -Z macro-backtrace for more info) + +error: unreachable statement + --> $DIR/diverge-causes-unreachable-code.rs:33:5 + | +LL | match *ptr { ! }; + | ---------------- any code following this `match` expression is unreachable, as all arms diverge +LL | } +LL | println!(); + | ^^^^^^^^^^ unreachable statement + | + = note: this error originates in the macro `$crate::print` which comes from the expansion of the macro `println` (in Nightly builds, run with -Z macro-backtrace for more info) + +error: aborting due to 3 previous errors + diff --git a/tests/ui/rfcs/rfc-0000-never_patterns/diverges-not.rs b/tests/ui/rfcs/rfc-0000-never_patterns/diverges-not.rs new file mode 100644 index 0000000000000..6b85ada3aadee --- /dev/null +++ b/tests/ui/rfcs/rfc-0000-never_patterns/diverges-not.rs @@ -0,0 +1,56 @@ +#![feature(never_patterns)] +#![feature(let_chains)] +#![allow(incomplete_features)] +#![deny(unreachable_patterns)] + +fn main() {} + +enum Void {} + +// Contrast with `./diverges.rs`: merely having an empty type around isn't enough to diverge. + +fn wild_void(_: Void) -> u32 {} +//~^ ERROR: mismatched types + +fn wild_let() -> u32 { + let ptr: *const Void = std::ptr::null(); + unsafe { + //~^ ERROR: mismatched types + let _ = *ptr; + } +} + +fn wild_match() -> u32 { + let ptr: *const Void = std::ptr::null(); + unsafe { + match *ptr { + _ => {} //~ ERROR: mismatched types + } + } +} + +fn binding_void(_x: Void) -> u32 {} +//~^ ERROR: mismatched types + +fn binding_let() -> u32 { + let ptr: *const Void = std::ptr::null(); + unsafe { + //~^ ERROR: mismatched types + let _x = *ptr; + } +} + +fn binding_match() -> u32 { + let ptr: *const Void = std::ptr::null(); + unsafe { + match *ptr { + _x => {} //~ ERROR: mismatched types + } + } +} + +// Don't confuse this with a `let !` statement. +fn let_chain(x: Void) -> u32 { + if let true = true && let ! = x {} + //~^ ERROR: mismatched types +} diff --git a/tests/ui/rfcs/rfc-0000-never_patterns/diverges-not.stderr b/tests/ui/rfcs/rfc-0000-never_patterns/diverges-not.stderr new file mode 100644 index 0000000000000..08a1bbe9bffac --- /dev/null +++ b/tests/ui/rfcs/rfc-0000-never_patterns/diverges-not.stderr @@ -0,0 +1,55 @@ +error[E0308]: mismatched types + --> $DIR/diverges-not.rs:12:26 + | +LL | fn wild_void(_: Void) -> u32 {} + | --------- ^^^ expected `u32`, found `()` + | | + | implicitly returns `()` as its body has no tail or `return` expression + +error[E0308]: mismatched types + --> $DIR/diverges-not.rs:17:5 + | +LL | / unsafe { +LL | | +LL | | let _ = *ptr; +LL | | } + | |_____^ expected `u32`, found `()` + +error[E0308]: mismatched types + --> $DIR/diverges-not.rs:27:18 + | +LL | _ => {} + | ^^ expected `u32`, found `()` + +error[E0308]: mismatched types + --> $DIR/diverges-not.rs:32:30 + | +LL | fn binding_void(_x: Void) -> u32 {} + | ------------ ^^^ expected `u32`, found `()` + | | + | implicitly returns `()` as its body has no tail or `return` expression + +error[E0308]: mismatched types + --> $DIR/diverges-not.rs:37:5 + | +LL | / unsafe { +LL | | +LL | | let _x = *ptr; +LL | | } + | |_____^ expected `u32`, found `()` + +error[E0308]: mismatched types + --> $DIR/diverges-not.rs:47:19 + | +LL | _x => {} + | ^^ expected `u32`, found `()` + +error[E0308]: mismatched types + --> $DIR/diverges-not.rs:54:37 + | +LL | if let true = true && let ! = x {} + | ^^ expected `u32`, found `()` + +error: aborting due to 7 previous errors + +For more information about this error, try `rustc --explain E0308`. diff --git a/tests/ui/rfcs/rfc-0000-never_patterns/diverges.rs b/tests/ui/rfcs/rfc-0000-never_patterns/diverges.rs new file mode 100644 index 0000000000000..40aa2bd29e594 --- /dev/null +++ b/tests/ui/rfcs/rfc-0000-never_patterns/diverges.rs @@ -0,0 +1,29 @@ +// check-pass +#![feature(never_patterns)] +#![allow(incomplete_features)] +#![deny(unreachable_patterns)] + +fn main() {} + +enum Void {} + +// A never pattern alone diverges. + +fn never_arg(!: Void) -> u32 {} + +fn ref_never_arg(&!: &Void) -> u32 {} + +// fn never_let() -> u32 { +// let ptr: *const Void = std::ptr::null(); +// unsafe { +// let ! = *ptr; +// } +// } + +fn never_match() -> u32 { + let ptr: *const Void = std::ptr::null(); + unsafe { + match *ptr { ! }; + } + println!(); // Ensures this typechecks because of divergence. +}