src/librustc/middle/entry.rs

   1 // Copyright 2012 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution and at
   3 // http://rust-lang.org/COPYRIGHT.
   4 //
   5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   8 // option. This file may not be copied, modified, or distributed
   9 // except according to those terms.
  10
  11
  12 use dep_graph::DepNode;
  13 use hir::map as ast_map;
  14 use hir::def_id::{CRATE_DEF_INDEX};
  15 use session::{config, Session};
  16 use syntax::ast::NodeId;
  17 use syntax::attr;
  18 use syntax::entry::EntryPointType;
  19 use syntax_pos::Span;
  20 use hir::{Item, ItemFn};
  21 use hir::intravisit::Visitor;
  22
  23 struct EntryContext<'a, 'tcx: 'a> {
  24     session: &'a Session,
  25
  26     map: &'a ast_map::Map<'tcx>,
  27
  28     // The top-level function called 'main'
  29     main_fn: Option<(NodeId, Span)>,
  30
  31     // The function that has attribute named 'main'
  32     attr_main_fn: Option<(NodeId, Span)>,
  33
  34     // The function that has the attribute 'start' on it
  35     start_fn: Option<(NodeId, Span)>,
  36
  37     // The functions that one might think are 'main' but aren't, e.g.
  38     // main functions not defined at the top level. For diagnostics.
  39     non_main_fns: Vec<(NodeId, Span)> ,
  40 }
  41
  42 impl<'a, 'tcx> Visitor<'tcx> for EntryContext<'a, 'tcx> {
  43     fn visit_item(&mut self, item: &'tcx Item) {
  44         let def_id = self.map.local_def_id(item.id);
  45         let def_key = self.map.def_key(def_id);
  46         let at_root = def_key.parent == Some(CRATE_DEF_INDEX);
  47         find_item(item, self, at_root);
  48     }
  49 }
  50
  51 pub fn find_entry_point(session: &Session, ast_map: &ast_map::Map) {
  52     let _task = ast_map.dep_graph.in_task(DepNode::EntryPoint);
  53
  54     let any_exe = session.crate_types.borrow().iter().any(|ty| {
  55         *ty == config::CrateTypeExecutable
  56     });
  57     if !any_exe {
  58         // No need to find a main function
  59         return
  60     }
  61
  62     // If the user wants no main function at all, then stop here.
  63     if attr::contains_name(&ast_map.krate().attrs, "no_main") {
  64         session.entry_type.set(Some(config::EntryNone));
  65         return
  66     }
  67
  68     let mut ctxt = EntryContext {
  69         session: session,
  70         map: ast_map,
  71         main_fn: None,
  72         attr_main_fn: None,
  73         start_fn: None,
  74         non_main_fns: Vec::new(),
  75     };
  76
  77     ast_map.krate().visit_all_items(&mut ctxt);
  78
  79     configure_main(&mut ctxt);
  80 }
  81
  82 // Beware, this is duplicated in libsyntax/entry.rs, make sure to keep
  83 // them in sync.
  84 fn entry_point_type(item: &Item, at_root: bool) -> EntryPointType {
  85     match item.node {
  86         ItemFn(..) => {
  87             if attr::contains_name(&item.attrs, "start") {
  88                 EntryPointType::Start
  89             } else if attr::contains_name(&item.attrs, "main") {
  90                 EntryPointType::MainAttr
  91             } else if item.name.as_str() == "main" {
  92                 if at_root {
  93                     // This is a top-level function so can be 'main'
  94                     EntryPointType::MainNamed
  95                 } else {
  96                     EntryPointType::OtherMain
  97                 }
  98             } else {
  99                 EntryPointType::None
 100             }
 101         }
 102         _ => EntryPointType::None,
 103     }
 104 }
 105
 106
 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.id, item.span));
 112             } else {
 113                 span_err!(ctxt.session, item.span, E0136,
 114                           "multiple 'main' functions");
 115             }
 116         },
 117         EntryPointType::OtherMain => {
 118             ctxt.non_main_fns.push((item.id, item.span));
 119         },
 120         EntryPointType::MainAttr => {
 121             if ctxt.attr_main_fn.is_none() {
 122                 ctxt.attr_main_fn = Some((item.id, item.span));
 123             } else {
 124                 struct_span_err!(ctxt.session, item.span, E0137,
 125                           "multiple functions with a #[main] attribute")
 126                 .span_label(item.span, &format!("additional #[main] function"))
 127                 .span_label(ctxt.attr_main_fn.unwrap().1, &format!("first #[main] function"))
 128                 .emit();
 129             }
 130         },
 131         EntryPointType::Start => {
 132             if ctxt.start_fn.is_none() {
 133                 ctxt.start_fn = Some((item.id, item.span));
 134             } else {
 135                 struct_span_err!(
 136                     ctxt.session, item.span, E0138,
 137                     "multiple 'start' functions")
 138                     .span_label(ctxt.start_fn.unwrap().1,
 139                                 &format!("previous `start` function here"))
 140                     .span_label(item.span, &format!("multiple `start` functions"))
 141                     .emit();
 142             }
 143         },
 144         EntryPointType::None => ()
 145     }
 146 }
 147
 148 fn configure_main(this: &mut EntryContext) {
 149     if this.start_fn.is_some() {
 150         *this.session.entry_fn.borrow_mut() = this.start_fn;
 151         this.session.entry_type.set(Some(config::EntryStart));
 152     } else if this.attr_main_fn.is_some() {
 153         *this.session.entry_fn.borrow_mut() = this.attr_main_fn;
 154         this.session.entry_type.set(Some(config::EntryMain));
 155     } else if this.main_fn.is_some() {
 156         *this.session.entry_fn.borrow_mut() = this.main_fn;
 157         this.session.entry_type.set(Some(config::EntryMain));
 158     } else {
 159         // No main function
 160         let mut err = this.session.struct_err("main function not found");
 161         if !this.non_main_fns.is_empty() {
 162             // There were some functions named 'main' though. Try to give the user a hint.
 163             err.note("the main function must be defined at the crate level \
 164                       but you have one or more functions named 'main' that are not \
 165                       defined at the crate level. Either move the definition or \
 166                       attach the `#[main]` attribute to override this behavior.");
 167             for &(_, span) in &this.non_main_fns {
 168                 err.span_note(span, "here is a function named 'main'");
 169             }
 170             err.emit();
 171             this.session.abort_if_errors();
 172         } else {
 173             err.emit();
 174         }
 175     }
 176 }