1 use rustc::hir::def_id::{CrateNum, DefId, CRATE_DEF_INDEX, LOCAL_CRATE};
2 use rustc::hir::itemlikevisit::ItemLikeVisitor;
3 use rustc::hir::map as hir_map;
4 use rustc::hir::{HirId, ImplItem, Item, ItemKind, TraitItem};
5 use rustc::session::config::EntryFnType;
6 use rustc::session::{config, Session};
7 use rustc::ty::query::Providers;
9 use rustc_span::symbol::sym;
12 use syntax::entry::EntryPointType;
14 use rustc_error_codes::*;
16 struct EntryContext<'a, 'tcx> {
19 map: &'a hir_map::Map<'tcx>,
21 /// The top-level function called `main`.
22 main_fn: Option<(HirId, Span)>,
24 /// The function that has attribute named `main`.
25 attr_main_fn: Option<(HirId, Span)>,
27 /// The function that has the attribute 'start' on it.
28 start_fn: Option<(HirId, Span)>,
30 /// The functions that one might think are `main` but aren't, e.g.
31 /// main functions not defined at the top level. For diagnostics.
32 non_main_fns: Vec<(HirId, Span)>,
35 impl<'a, 'tcx> ItemLikeVisitor<'tcx> for EntryContext<'a, 'tcx> {
36 fn visit_item(&mut self, item: &'tcx Item<'tcx>) {
37 let def_id = self.map.local_def_id(item.hir_id);
38 let def_key = self.map.def_key(def_id);
39 let at_root = def_key.parent == Some(CRATE_DEF_INDEX);
40 find_item(item, self, at_root);
43 fn visit_trait_item(&mut self, _trait_item: &'tcx TraitItem<'tcx>) {
44 // Entry fn is never a trait item.
47 fn visit_impl_item(&mut self, _impl_item: &'tcx ImplItem<'tcx>) {
48 // Entry fn is never a trait item.
52 fn entry_fn(tcx: TyCtxt<'_>, cnum: CrateNum) -> Option<(DefId, EntryFnType)> {
53 assert_eq!(cnum, LOCAL_CRATE);
56 tcx.sess.crate_types.borrow().iter().any(|ty| *ty == config::CrateType::Executable);
58 // No need to find a main function.
62 // If the user wants no main function at all, then stop here.
63 if attr::contains_name(&tcx.hir().krate().attrs, sym::no_main) {
67 let mut ctxt = EntryContext {
73 non_main_fns: Vec::new(),
76 tcx.hir().krate().visit_all_item_likes(&mut ctxt);
78 configure_main(tcx, &ctxt)
81 // Beware, this is duplicated in `libsyntax/entry.rs`, so make sure to keep
83 fn entry_point_type(item: &Item<'_>, at_root: bool) -> EntryPointType {
86 if attr::contains_name(&item.attrs, sym::start) {
88 } else if attr::contains_name(&item.attrs, sym::main) {
89 EntryPointType::MainAttr
90 } else if item.ident.name == sym::main {
92 // This is a top-level function so can be `main`.
93 EntryPointType::MainNamed
95 EntryPointType::OtherMain
101 _ => EntryPointType::None,
105 fn find_item(item: &Item<'_>, ctxt: &mut EntryContext<'_, '_>, at_root: bool) {
106 match entry_point_type(item, at_root) {
107 EntryPointType::MainNamed => {
108 if ctxt.main_fn.is_none() {
109 ctxt.main_fn = Some((item.hir_id, item.span));
111 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 => (),
146 fn configure_main(tcx: TyCtxt<'_>, visitor: &EntryContext<'_, '_>) -> Option<(DefId, EntryFnType)> {
147 if let Some((hir_id, _)) = visitor.start_fn {
148 Some((tcx.hir().local_def_id(hir_id), EntryFnType::Start))
149 } else if let Some((hir_id, _)) = visitor.attr_main_fn {
150 Some((tcx.hir().local_def_id(hir_id), EntryFnType::Main))
151 } else if let Some((hir_id, _)) = visitor.main_fn {
152 Some((tcx.hir().local_def_id(hir_id), EntryFnType::Main))
154 no_main_err(tcx, visitor);
159 fn no_main_err(tcx: TyCtxt<'_>, visitor: &EntryContext<'_, '_>) {
160 let sp = tcx.hir().krate().span;
161 if *tcx.sess.parse_sess.reached_eof.borrow() {
162 // There's an unclosed brace that made the parser reach `Eof`, we shouldn't complain about
163 // the missing `fn main()` then as it might have been hidden inside an unclosed block.
164 tcx.sess.delay_span_bug(sp, "`main` not found, but expected unclosed brace error");
168 // There is no main function.
169 let mut err = struct_err!(
172 "`main` function not found in crate `{}`",
173 tcx.crate_name(LOCAL_CRATE)
175 let filename = &tcx.sess.local_crate_source_file;
176 let note = if !visitor.non_main_fns.is_empty() {
177 for &(_, span) in &visitor.non_main_fns {
178 err.span_note(span, "here is a function named `main`");
180 err.note("you have one or more functions named `main` not defined at the crate level");
182 "either move the `main` function definitions or attach the `#[main]` attribute \
185 // There were some functions named `main` though. Try to give the user a hint.
187 "the main function must be defined at the crate level{}",
188 filename.as_ref().map(|f| format!(" (in `{}`)", f.display())).unwrap_or_default()
190 } else if let Some(filename) = filename {
191 format!("consider adding a `main` function to `{}`", filename.display())
193 String::from("consider adding a `main` function at the crate level")
195 // The file may be empty, which leads to the diagnostic machinery not emitting this
196 // note. This is a relatively simple way to detect that case and emit a span-less
198 if let Ok(_) = tcx.sess.source_map().lookup_line(sp.lo()) {
200 err.span_label(sp, ¬e);
204 if tcx.sess.teach(&err.get_code().unwrap()) {
206 "If you don't know the basics of Rust, you can go look to the Rust Book \
207 to get started: https://doc.rust-lang.org/book/",
213 pub fn find_entry_point(tcx: TyCtxt<'_>) -> Option<(DefId, EntryFnType)> {
214 tcx.entry_fn(LOCAL_CRATE)
217 pub fn provide(providers: &mut Providers<'_>) {
218 *providers = Providers { entry_fn, ..*providers };