1 use rustc_ast::entry::EntryPointType;
2 use rustc_errors::struct_span_err;
3 use rustc_hir::def_id::{CrateNum, LocalDefId, CRATE_DEF_INDEX, LOCAL_CRATE};
4 use rustc_hir::itemlikevisit::ItemLikeVisitor;
5 use rustc_hir::{ForeignItem, HirId, ImplItem, Item, ItemKind, TraitItem};
6 use rustc_middle::hir::map::Map;
7 use rustc_middle::ty::query::Providers;
8 use rustc_middle::ty::TyCtxt;
9 use rustc_session::config::{CrateType, EntryFnType};
10 use rustc_session::Session;
11 use rustc_span::symbol::sym;
12 use rustc_span::{Span, DUMMY_SP};
14 struct EntryContext<'a, 'tcx> {
19 /// The top-level function called `main`.
20 main_fn: Option<(HirId, Span)>,
22 /// The function that has attribute named `main`.
23 attr_main_fn: Option<(HirId, Span)>,
25 /// The function that has the attribute 'start' on it.
26 start_fn: Option<(HirId, Span)>,
28 /// The functions that one might think are `main` but aren't, e.g.
29 /// main functions not defined at the top level. For diagnostics.
30 non_main_fns: Vec<(HirId, Span)>,
33 impl<'a, 'tcx> ItemLikeVisitor<'tcx> for EntryContext<'a, 'tcx> {
34 fn visit_item(&mut self, item: &'tcx Item<'tcx>) {
35 let def_id = self.map.local_def_id(item.hir_id);
36 let def_key = self.map.def_key(def_id);
37 let at_root = def_key.parent == Some(CRATE_DEF_INDEX);
38 find_item(item, self, at_root);
41 fn visit_trait_item(&mut self, _trait_item: &'tcx TraitItem<'tcx>) {
42 // Entry fn is never a trait item.
45 fn visit_impl_item(&mut self, _impl_item: &'tcx ImplItem<'tcx>) {
46 // Entry fn is never a trait item.
49 fn visit_foreign_item(&mut self, _: &'tcx ForeignItem<'tcx>) {
50 // Entry fn is never a foreign item.
54 fn entry_fn(tcx: TyCtxt<'_>, cnum: CrateNum) -> Option<(LocalDefId, EntryFnType)> {
55 assert_eq!(cnum, LOCAL_CRATE);
57 let any_exe = tcx.sess.crate_types().iter().any(|ty| *ty == CrateType::Executable);
59 // No need to find a main function.
63 // If the user wants no main function at all, then stop here.
64 if tcx.sess.contains_name(&tcx.hir().krate().item.attrs, sym::no_main) {
68 let mut ctxt = EntryContext {
74 non_main_fns: Vec::new(),
77 tcx.hir().krate().visit_all_item_likes(&mut ctxt);
79 configure_main(tcx, &ctxt)
82 // Beware, this is duplicated in `librustc_builtin_macros/test_harness.rs`
83 // (with `ast::Item`), so make sure to keep them in sync.
84 fn entry_point_type(sess: &Session, item: &Item<'_>, at_root: bool) -> EntryPointType {
85 if sess.contains_name(&item.attrs, sym::start) {
87 } else if sess.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
101 fn throw_attr_err(sess: &Session, span: Span, attr: &str) {
102 sess.struct_span_err(span, &format!("`{}` attribute can only be used on functions", attr))
106 fn find_item(item: &Item<'_>, ctxt: &mut EntryContext<'_, '_>, at_root: bool) {
107 match entry_point_type(&ctxt.session, item, at_root) {
108 EntryPointType::None => (),
109 _ if !matches!(item.kind, ItemKind::Fn(..)) => {
110 if let Some(attr) = ctxt.session.find_by_name(item.attrs, sym::start) {
111 throw_attr_err(&ctxt.session, attr.span, "start");
113 if let Some(attr) = ctxt.session.find_by_name(item.attrs, sym::main) {
114 throw_attr_err(&ctxt.session, attr.span, "main");
117 EntryPointType::MainNamed => {
118 if ctxt.main_fn.is_none() {
119 ctxt.main_fn = Some((item.hir_id, item.span));
121 struct_span_err!(ctxt.session, item.span, E0136, "multiple `main` functions")
125 EntryPointType::OtherMain => {
126 ctxt.non_main_fns.push((item.hir_id, item.span));
128 EntryPointType::MainAttr => {
129 if ctxt.attr_main_fn.is_none() {
130 ctxt.attr_main_fn = Some((item.hir_id, item.span));
136 "multiple functions with a `#[main]` attribute"
138 .span_label(item.span, "additional `#[main]` function")
139 .span_label(ctxt.attr_main_fn.unwrap().1, "first `#[main]` function")
143 EntryPointType::Start => {
144 if ctxt.start_fn.is_none() {
145 ctxt.start_fn = Some((item.hir_id, item.span));
147 struct_span_err!(ctxt.session, item.span, E0138, "multiple `start` functions")
148 .span_label(ctxt.start_fn.unwrap().1, "previous `#[start]` function here")
149 .span_label(item.span, "multiple `start` functions")
158 visitor: &EntryContext<'_, '_>,
159 ) -> Option<(LocalDefId, EntryFnType)> {
160 if let Some((hir_id, _)) = visitor.start_fn {
161 Some((tcx.hir().local_def_id(hir_id), EntryFnType::Start))
162 } else if let Some((hir_id, _)) = visitor.attr_main_fn {
163 Some((tcx.hir().local_def_id(hir_id), EntryFnType::Main))
164 } else if let Some((hir_id, _)) = visitor.main_fn {
165 Some((tcx.hir().local_def_id(hir_id), EntryFnType::Main))
167 no_main_err(tcx, visitor);
172 fn no_main_err(tcx: TyCtxt<'_>, visitor: &EntryContext<'_, '_>) {
173 let sp = tcx.hir().krate().item.span;
174 if *tcx.sess.parse_sess.reached_eof.borrow() {
175 // There's an unclosed brace that made the parser reach `Eof`, we shouldn't complain about
176 // the missing `fn main()` then as it might have been hidden inside an unclosed block.
177 tcx.sess.delay_span_bug(sp, "`main` not found, but expected unclosed brace error");
181 // There is no main function.
182 let mut err = struct_span_err!(
186 "`main` function not found in crate `{}`",
187 tcx.crate_name(LOCAL_CRATE)
189 let filename = &tcx.sess.local_crate_source_file;
190 let note = if !visitor.non_main_fns.is_empty() {
191 for &(_, span) in &visitor.non_main_fns {
192 err.span_note(span, "here is a function named `main`");
194 err.note("you have one or more functions named `main` not defined at the crate level");
196 "either move the `main` function definitions or attach the `#[main]` attribute \
199 // There were some functions named `main` though. Try to give the user a hint.
201 "the main function must be defined at the crate level{}",
202 filename.as_ref().map(|f| format!(" (in `{}`)", f.display())).unwrap_or_default()
204 } else if let Some(filename) = filename {
205 format!("consider adding a `main` function to `{}`", filename.display())
207 String::from("consider adding a `main` function at the crate level")
209 // The file may be empty, which leads to the diagnostic machinery not emitting this
210 // note. This is a relatively simple way to detect that case and emit a span-less
212 if tcx.sess.source_map().lookup_line(sp.lo()).is_ok() {
214 err.span_label(sp, ¬e);
218 if tcx.sess.teach(&err.get_code().unwrap()) {
220 "If you don't know the basics of Rust, you can go look to the Rust Book \
221 to get started: https://doc.rust-lang.org/book/",
227 pub fn find_entry_point(tcx: TyCtxt<'_>) -> Option<(LocalDefId, EntryFnType)> {
228 tcx.entry_fn(LOCAL_CRATE)
231 pub fn provide(providers: &mut Providers) {
232 *providers = Providers { entry_fn, ..*providers };