1 use rustc::hir::map as hir_map;
2 use rustc::hir::def_id::{CrateNum, CRATE_DEF_INDEX, DefId, LOCAL_CRATE};
3 use rustc::session::{config, Session};
4 use rustc::session::config::EntryFnType;
6 use syntax::entry::EntryPointType;
7 use syntax::symbol::sym;
9 use rustc::hir::{HirId, Item, ItemKind, ImplItem, TraitItem};
10 use rustc::hir::itemlikevisit::ItemLikeVisitor;
11 use rustc::ty::TyCtxt;
12 use rustc::ty::query::Providers;
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) {
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) {
44 // Entry fn is never a trait item.
47 fn visit_impl_item(&mut self, _impl_item: &'tcx ImplItem) {
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);
55 let any_exe = tcx.sess.crate_types.borrow().iter().any(|ty| {
56 *ty == config::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 attr::contains_name(&tcx.hir().krate().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 `libsyntax/entry.rs`, so make sure to keep
84 fn entry_point_type(item: &Item, at_root: bool) -> EntryPointType {
87 if attr::contains_name(&item.attrs, sym::start) {
89 } else if attr::contains_name(&item.attrs, sym::main) {
90 EntryPointType::MainAttr
91 } else if item.ident.name == sym::main {
93 // This is a top-level function so can be `main`.
94 EntryPointType::MainNamed
96 EntryPointType::OtherMain
102 _ => EntryPointType::None,
107 fn find_item(item: &Item, ctxt: &mut EntryContext<'_, '_>, at_root: bool) {
108 match entry_point_type(item, at_root) {
109 EntryPointType::MainNamed => {
110 if ctxt.main_fn.is_none() {
111 ctxt.main_fn = Some((item.hir_id, item.span));
113 span_err!(ctxt.session, item.span, E0136,
114 "multiple `main` functions");
117 EntryPointType::OtherMain => {
118 ctxt.non_main_fns.push((item.hir_id, item.span));
120 EntryPointType::MainAttr => {
121 if ctxt.attr_main_fn.is_none() {
122 ctxt.attr_main_fn = Some((item.hir_id, item.span));
124 struct_span_err!(ctxt.session, item.span, E0137,
125 "multiple functions with a `#[main]` attribute")
126 .span_label(item.span, "additional `#[main]` function")
127 .span_label(ctxt.attr_main_fn.unwrap().1, "first `#[main]` function")
131 EntryPointType::Start => {
132 if ctxt.start_fn.is_none() {
133 ctxt.start_fn = Some((item.hir_id, item.span));
135 struct_span_err!(ctxt.session, item.span, E0138, "multiple `start` functions")
136 .span_label(ctxt.start_fn.unwrap().1, "previous `start` function here")
137 .span_label(item.span, "multiple `start` functions")
141 EntryPointType::None => (),
145 fn configure_main(tcx: TyCtxt<'_>, visitor: &EntryContext<'_, '_>) -> Option<(DefId, EntryFnType)> {
146 if let Some((hir_id, _)) = visitor.start_fn {
147 Some((tcx.hir().local_def_id(hir_id), EntryFnType::Start))
148 } else if let Some((hir_id, _)) = visitor.attr_main_fn {
149 Some((tcx.hir().local_def_id(hir_id), EntryFnType::Main))
150 } else if let Some((hir_id, _)) = visitor.main_fn {
151 Some((tcx.hir().local_def_id(hir_id), EntryFnType::Main))
153 no_main_err(tcx, visitor);
158 fn no_main_err(tcx: TyCtxt<'_>, visitor: &EntryContext<'_, '_>) {
159 let sp = tcx.hir().krate().span;
160 if *tcx.sess.parse_sess.reached_eof.borrow() {
161 // There's an unclosed brace that made the parser reach `Eof`, we shouldn't complain about
162 // the missing `fn main()` then as it might have been hidden inside an unclosed block.
163 tcx.sess.delay_span_bug(sp, "`main` not found, but expected unclosed brace error");
167 // There is no main function.
168 let mut err = struct_err!(tcx.sess, E0601,
169 "`main` function not found in crate `{}`", tcx.crate_name(LOCAL_CRATE));
170 let filename = &tcx.sess.local_crate_source_file;
171 let note = if !visitor.non_main_fns.is_empty() {
172 for &(_, span) in &visitor.non_main_fns {
173 err.span_note(span, "here is a function named `main`");
175 err.note("you have one or more functions named `main` not defined at the crate level");
176 err.help("either move the `main` function definitions or attach the `#[main]` attribute \
178 // There were some functions named `main` though. Try to give the user a hint.
179 format!("the main function must be defined at the crate level{}",
180 filename.as_ref().map(|f| format!(" (in `{}`)", f.display())).unwrap_or_default())
181 } else if let Some(filename) = filename {
182 format!("consider adding a `main` function to `{}`", filename.display())
184 String::from("consider adding a `main` function at the crate level")
186 // The file may be empty, which leads to the diagnostic machinery not emitting this
187 // note. This is a relatively simple way to detect that case and emit a span-less
189 if let Ok(_) = tcx.sess.source_map().lookup_line(sp.lo()) {
191 err.span_label(sp, ¬e);
195 if tcx.sess.teach(&err.get_code().unwrap()) {
196 err.note("If you don't know the basics of Rust, you can go look to the Rust Book \
197 to get started: https://doc.rust-lang.org/book/");
202 pub fn find_entry_point(tcx: TyCtxt<'_>) -> Option<(DefId, EntryFnType)> {
203 tcx.entry_fn(LOCAL_CRATE)
206 pub fn provide(providers: &mut Providers<'_>) {
207 *providers = Providers {