2 use rustc_ast::entry::EntryPointType;
3 use rustc_errors::struct_span_err;
4 use rustc_hir::def_id::{CrateNum, LocalDefId, CRATE_DEF_INDEX, LOCAL_CRATE};
5 use rustc_hir::itemlikevisit::ItemLikeVisitor;
6 use rustc_hir::{HirId, ImplItem, Item, ItemKind, TraitItem};
7 use rustc_middle::hir::map::Map;
8 use rustc_middle::ty::query::Providers;
9 use rustc_middle::ty::TyCtxt;
10 use rustc_session::config::EntryFnType;
11 use rustc_session::{config, Session};
12 use rustc_span::symbol::sym;
13 use rustc_span::{Span, DUMMY_SP};
15 struct EntryContext<'a, 'tcx> {
20 /// The top-level function called `main`.
21 main_fn: Option<(HirId, Span)>,
23 /// The function that has attribute named `main`.
24 attr_main_fn: Option<(HirId, Span)>,
26 /// The function that has the attribute 'start' on it.
27 start_fn: Option<(HirId, Span)>,
29 /// The functions that one might think are `main` but aren't, e.g.
30 /// main functions not defined at the top level. For diagnostics.
31 non_main_fns: Vec<(HirId, Span)>,
34 impl<'a, 'tcx> ItemLikeVisitor<'tcx> for EntryContext<'a, 'tcx> {
35 fn visit_item(&mut self, item: &'tcx Item<'tcx>) {
36 let def_id = self.map.local_def_id(item.hir_id);
37 let def_key = self.map.def_key(def_id);
38 let at_root = def_key.parent == Some(CRATE_DEF_INDEX);
39 find_item(item, self, at_root);
42 fn visit_trait_item(&mut self, _trait_item: &'tcx TraitItem<'tcx>) {
43 // Entry fn is never a trait item.
46 fn visit_impl_item(&mut self, _impl_item: &'tcx ImplItem<'tcx>) {
47 // Entry fn is never a trait item.
51 fn entry_fn(tcx: TyCtxt<'_>, cnum: CrateNum) -> Option<(LocalDefId, EntryFnType)> {
52 assert_eq!(cnum, LOCAL_CRATE);
55 tcx.sess.crate_types.borrow().iter().any(|ty| *ty == config::CrateType::Executable);
57 // No need to find a main function.
61 // If the user wants no main function at all, then stop here.
62 if attr::contains_name(&tcx.hir().krate().item.attrs, sym::no_main) {
66 let mut ctxt = EntryContext {
72 non_main_fns: Vec::new(),
75 tcx.hir().krate().visit_all_item_likes(&mut ctxt);
77 configure_main(tcx, &ctxt)
80 // Beware, this is duplicated in `librustc_ast/entry.rs`, so make sure to keep
82 fn entry_point_type(item: &Item<'_>, at_root: bool) -> EntryPointType {
85 if attr::contains_name(&item.attrs, sym::start) {
87 } else if attr::contains_name(&item.attrs, sym::main) {
88 EntryPointType::MainAttr
89 } else if item.ident.name == sym::main {
91 // This is a top-level function so can be `main`.
92 EntryPointType::MainNamed
94 EntryPointType::OtherMain
100 _ => EntryPointType::None,
104 fn find_item(item: &Item<'_>, ctxt: &mut EntryContext<'_, '_>, at_root: bool) {
105 match entry_point_type(item, at_root) {
106 EntryPointType::MainNamed => {
107 if ctxt.main_fn.is_none() {
108 ctxt.main_fn = Some((item.hir_id, item.span));
110 struct_span_err!(ctxt.session, item.span, E0136, "multiple `main` functions")
114 EntryPointType::OtherMain => {
115 ctxt.non_main_fns.push((item.hir_id, item.span));
117 EntryPointType::MainAttr => {
118 if ctxt.attr_main_fn.is_none() {
119 ctxt.attr_main_fn = Some((item.hir_id, item.span));
125 "multiple functions with a `#[main]` attribute"
127 .span_label(item.span, "additional `#[main]` function")
128 .span_label(ctxt.attr_main_fn.unwrap().1, "first `#[main]` function")
132 EntryPointType::Start => {
133 if ctxt.start_fn.is_none() {
134 ctxt.start_fn = Some((item.hir_id, item.span));
136 struct_span_err!(ctxt.session, item.span, E0138, "multiple `start` functions")
137 .span_label(ctxt.start_fn.unwrap().1, "previous `#[start]` function here")
138 .span_label(item.span, "multiple `start` functions")
142 EntryPointType::None => (),
148 visitor: &EntryContext<'_, '_>,
149 ) -> Option<(LocalDefId, EntryFnType)> {
150 if let Some((hir_id, _)) = visitor.start_fn {
151 Some((tcx.hir().local_def_id(hir_id), EntryFnType::Start))
152 } else if let Some((hir_id, _)) = visitor.attr_main_fn {
153 Some((tcx.hir().local_def_id(hir_id), EntryFnType::Main))
154 } else if let Some((hir_id, _)) = visitor.main_fn {
155 Some((tcx.hir().local_def_id(hir_id), EntryFnType::Main))
157 no_main_err(tcx, visitor);
162 fn no_main_err(tcx: TyCtxt<'_>, visitor: &EntryContext<'_, '_>) {
163 let sp = tcx.hir().krate().item.span;
164 if *tcx.sess.parse_sess.reached_eof.borrow() {
165 // There's an unclosed brace that made the parser reach `Eof`, we shouldn't complain about
166 // the missing `fn main()` then as it might have been hidden inside an unclosed block.
167 tcx.sess.delay_span_bug(sp, "`main` not found, but expected unclosed brace error");
171 // There is no main function.
172 let mut err = struct_span_err!(
176 "`main` function not found in crate `{}`",
177 tcx.crate_name(LOCAL_CRATE)
179 let filename = &tcx.sess.local_crate_source_file;
180 let note = if !visitor.non_main_fns.is_empty() {
181 for &(_, span) in &visitor.non_main_fns {
182 err.span_note(span, "here is a function named `main`");
184 err.note("you have one or more functions named `main` not defined at the crate level");
186 "either move the `main` function definitions or attach the `#[main]` attribute \
189 // There were some functions named `main` though. Try to give the user a hint.
191 "the main function must be defined at the crate level{}",
192 filename.as_ref().map(|f| format!(" (in `{}`)", f.display())).unwrap_or_default()
194 } else if let Some(filename) = filename {
195 format!("consider adding a `main` function to `{}`", filename.display())
197 String::from("consider adding a `main` function at the crate level")
199 // The file may be empty, which leads to the diagnostic machinery not emitting this
200 // note. This is a relatively simple way to detect that case and emit a span-less
202 if tcx.sess.source_map().lookup_line(sp.lo()).is_ok() {
204 err.span_label(sp, ¬e);
208 if tcx.sess.teach(&err.get_code().unwrap()) {
210 "If you don't know the basics of Rust, you can go look to the Rust Book \
211 to get started: https://doc.rust-lang.org/book/",
217 pub fn find_entry_point(tcx: TyCtxt<'_>) -> Option<(LocalDefId, EntryFnType)> {
218 tcx.entry_fn(LOCAL_CRATE)
221 pub fn provide(providers: &mut Providers<'_>) {
222 *providers = Providers { entry_fn, ..*providers };