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Various improvements to entrypoint code
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This moves some code around and adds some documentation comments to make
it easier to understand what's going on with the entrypoint logic, which
is a bit complicated.

The only change in behavior is consolidating the error messages for
unix_sigpipe to make the code slightly simpler.
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Noratrieb committed May 4, 2024
1 parent 6d721dd commit a0ed1d0
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Showing 5 changed files with 48 additions and 43 deletions.
25 changes: 24 additions & 1 deletion compiler/rustc_ast/src/entry.rs
Original file line number Diff line number Diff line change
Expand Up @@ -4,11 +4,34 @@ use rustc_span::Symbol;

#[derive(Debug)]
pub enum EntryPointType {
/// This function is not an entrypoint.
None,
/// This is a function called `main` at the root level.
/// ```
/// fn main() {}
/// ```
MainNamed,
/// This is a function with the `#[rustc_main]` attribute.
/// Used by the testing harness to create the test entrypoint.
/// ```ignore (clashes with test entrypoint)
/// #[rustc_main]
/// fn main() {}
/// ```
RustcMainAttr,
/// This is a function with the `#[start]` attribute.
/// ```ignore (clashes with test entrypoint)
/// #[start]
/// fn main() {}
/// ```
Start,
OtherMain, // Not an entry point, but some other function named main
/// This function is **not** an entrypoint but simply named `main` (not at the root).
/// This is only used for diagnostics.
/// ```
/// mod meow {
/// fn main() {}

Check failure on line 31 in compiler/rustc_ast/src/entry.rs

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GitHub Actions / PR - x86_64-gnu-llvm-17

function `main` is never used
/// }
/// ```
OtherMain,
}

pub fn entry_point_type(
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2 changes: 1 addition & 1 deletion compiler/rustc_builtin_macros/src/test_harness.rs
Original file line number Diff line number Diff line change
Expand Up @@ -266,7 +266,7 @@ fn generate_test_harness(
///
/// By default this expands to
///
/// ```ignore UNSOLVED (I think I still need guidance for this one. Is it correct? Do we try to make it run? How do we nicely fill it out?)
/// ```ignore (messes with test internals)
/// #[rustc_main]
/// pub fn main() {
/// extern crate test;
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6 changes: 0 additions & 6 deletions compiler/rustc_passes/messages.ftl
Original file line number Diff line number Diff line change
Expand Up @@ -49,12 +49,6 @@ passes_attr_crate_level =
passes_attr_only_in_functions =
`{$attr}` attribute can only be used on functions
passes_attr_only_on_main =
`{$attr}` attribute can only be used on `fn main()`
passes_attr_only_on_root_main =
`{$attr}` attribute can only be used on root `fn main()`
passes_both_ffi_const_and_pure =
`#[ffi_const]` function cannot be `#[ffi_pure]`
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42 changes: 23 additions & 19 deletions compiler/rustc_passes/src/entry.rs
Original file line number Diff line number Diff line change
Expand Up @@ -18,10 +18,10 @@ use crate::errors::{
struct EntryContext<'tcx> {
tcx: TyCtxt<'tcx>,

/// The function that has attribute named `main`.
attr_main_fn: Option<(LocalDefId, Span)>,
/// The function has the `#[rustc_main]` attribute.
rustc_main_fn: Option<(LocalDefId, Span)>,

/// The function that has the attribute 'start' on it.
/// The function that has the attribute `#[start]` on it.
start_fn: Option<(LocalDefId, Span)>,

/// The functions that one might think are `main` but aren't, e.g.
Expand All @@ -42,10 +42,10 @@ fn entry_fn(tcx: TyCtxt<'_>, (): ()) -> Option<(DefId, EntryFnType)> {
}

let mut ctxt =
EntryContext { tcx, attr_main_fn: None, start_fn: None, non_main_fns: Vec::new() };
EntryContext { tcx, rustc_main_fn: None, start_fn: None, non_main_fns: Vec::new() };

for id in tcx.hir().items() {
find_item(id, &mut ctxt);
check_and_search_item(id, &mut ctxt);
}

configure_main(tcx, &ctxt)
Expand All @@ -56,7 +56,16 @@ fn attr_span_by_symbol(ctxt: &EntryContext<'_>, id: ItemId, sym: Symbol) -> Opti
attr::find_by_name(attrs, sym).map(|attr| attr.span)
}

fn find_item(id: ItemId, ctxt: &mut EntryContext<'_>) {
fn check_and_search_item(id: ItemId, ctxt: &mut EntryContext<'_>) {
if !matches!(ctxt.tcx.def_kind(id.owner_id), DefKind::Fn) {
for attr in [sym::start, sym::rustc_main] {
if let Some(span) = attr_span_by_symbol(ctxt, id, attr) {
ctxt.tcx.dcx().emit_err(AttrOnlyInFunctions { span, attr });
}
}
return;
}

let at_root = ctxt.tcx.opt_local_parent(id.owner_id.def_id) == Some(CRATE_DEF_ID);

let attrs = ctxt.tcx.hir().attrs(id.hir_id());
Expand All @@ -65,26 +74,20 @@ fn find_item(id: ItemId, ctxt: &mut EntryContext<'_>) {
at_root,
ctxt.tcx.opt_item_name(id.owner_id.to_def_id()),
);

match entry_point_type {
EntryPointType::None => (),
_ if !matches!(ctxt.tcx.def_kind(id.owner_id), DefKind::Fn) => {
for attr in [sym::start, sym::rustc_main] {
if let Some(span) = attr_span_by_symbol(ctxt, id, attr) {
ctxt.tcx.dcx().emit_err(AttrOnlyInFunctions { span, attr });
}
}
}
EntryPointType::MainNamed => (),
EntryPointType::None => {}
EntryPointType::MainNamed => {}
EntryPointType::OtherMain => {
ctxt.non_main_fns.push(ctxt.tcx.def_span(id.owner_id));
}
EntryPointType::RustcMainAttr => {
if ctxt.attr_main_fn.is_none() {
ctxt.attr_main_fn = Some((id.owner_id.def_id, ctxt.tcx.def_span(id.owner_id)));
if ctxt.rustc_main_fn.is_none() {
ctxt.rustc_main_fn = Some((id.owner_id.def_id, ctxt.tcx.def_span(id.owner_id)));
} else {
ctxt.tcx.dcx().emit_err(MultipleRustcMain {
span: ctxt.tcx.def_span(id.owner_id.to_def_id()),
first: ctxt.attr_main_fn.unwrap().1,
first: ctxt.rustc_main_fn.unwrap().1,
additional: ctxt.tcx.def_span(id.owner_id.to_def_id()),
});
}
Expand All @@ -107,10 +110,11 @@ fn find_item(id: ItemId, ctxt: &mut EntryContext<'_>) {
fn configure_main(tcx: TyCtxt<'_>, visitor: &EntryContext<'_>) -> Option<(DefId, EntryFnType)> {
if let Some((def_id, _)) = visitor.start_fn {
Some((def_id.to_def_id(), EntryFnType::Start))
} else if let Some((local_def_id, _)) = visitor.attr_main_fn {
} else if let Some((local_def_id, _)) = visitor.rustc_main_fn {
let def_id = local_def_id.to_def_id();
Some((def_id, EntryFnType::Main { sigpipe: sigpipe(tcx) }))
} else {
// The actual resolution of main happens in the resolver, this here
if let Some(main_def) = tcx.resolutions(()).main_def
&& let Some(def_id) = main_def.opt_fn_def_id()
{
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16 changes: 0 additions & 16 deletions compiler/rustc_passes/src/errors.rs
Original file line number Diff line number Diff line change
Expand Up @@ -1206,22 +1206,6 @@ pub struct NakedFunctionsMustUseNoreturn {
pub last_span: Span,
}

#[derive(Diagnostic)]
#[diag(passes_attr_only_on_main)]
pub struct AttrOnlyOnMain {
#[primary_span]
pub span: Span,
pub attr: Symbol,
}

#[derive(Diagnostic)]
#[diag(passes_attr_only_on_root_main)]
pub struct AttrOnlyOnRootMain {
#[primary_span]
pub span: Span,
pub attr: Symbol,
}

#[derive(Diagnostic)]
#[diag(passes_attr_only_in_functions)]
pub struct AttrOnlyInFunctions {
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