Rollup merge of rust-lang#48706 - ehuss:main-not-found-in-crate, r=estebank

Add crate name to "main function not found" error message.

Fixes rust-lang#44798 and rust-lang/cargo#4948.

I was wondering if it might be cleaner to update the ui tests to add a simple `fn main() {}` for the unrelated tests.  Let me know if you would prefer that.

Author: kennytm

src/librustc/middle/entry.rs

@@ -55,7 +55,9 @@ impl<'a, 'tcx> ItemLikeVisitor<'tcx> for EntryContext<'a, 'tcx> {
     }
 }
 
-pub fn find_entry_point(session: &Session, hir_map: &hir_map::Map) {
+pub fn find_entry_point(session: &Session,
+                        hir_map: &hir_map::Map,
+                        crate_name: &str) {
     let any_exe = session.crate_types.borrow().iter().any(|ty| {
         *ty == config::CrateTypeExecutable
     });
@@ -81,7 +83,7 @@ pub fn find_entry_point(session: &Session, hir_map: &hir_map::Map) {
 
     hir_map.krate().visit_all_item_likes(&mut ctxt);
 
-    configure_main(&mut ctxt);
+    configure_main(&mut ctxt, crate_name);
 }
 
 // Beware, this is duplicated in libsyntax/entry.rs, make sure to keep
@@ -150,7 +152,7 @@ fn find_item(item: &Item, ctxt: &mut EntryContext, at_root: bool) {
     }
 }
 
-fn configure_main(this: &mut EntryContext) {
+fn configure_main(this: &mut EntryContext, crate_name: &str) {
     if this.start_fn.is_some() {
         *this.session.entry_fn.borrow_mut() = this.start_fn;
         this.session.entry_type.set(Some(config::EntryStart));
@@ -162,7 +164,8 @@ fn configure_main(this: &mut EntryContext) {
         this.session.entry_type.set(Some(config::EntryMain));
     } else {
         // No main function
-        let mut err = struct_err!(this.session, E0601, "main function not found");
+        let mut err = struct_err!(this.session, E0601,
+            "`main` function not found in crate `{}`", crate_name);
         if !this.non_main_fns.is_empty() {
             // There were some functions named 'main' though. Try to give the user a hint.
             err.note("the main function must be defined at the crate level \
@@ -175,6 +178,9 @@ fn configure_main(this: &mut EntryContext) {
             err.emit();
             this.session.abort_if_errors();
         } else {
+            if let Some(ref filename) = this.session.local_crate_source_file {
+                err.note(&format!("consider adding a `main` function to `{}`", filename.display()));
+            }
             if this.session.teach(&err.get_code().unwrap()) {
                 err.note("If you don't know the basics of Rust, you can go look to the Rust Book \
                           to get started: https://doc.rust-lang.org/book/");

src/librustc_driver/driver.rs

@@ -979,7 +979,7 @@ pub fn phase_3_run_analysis_passes<'tcx, F, R>(trans: &TransCrate,
 
     time(sess,
          "looking for entry point",
-         || middle::entry::find_entry_point(sess, &hir_map));
+         || middle::entry::find_entry_point(sess, &hir_map, name));
 
     sess.plugin_registrar_fn.set(time(sess, "looking for plugin registrar", || {
         plugin::build::find_plugin_registrar(sess.diagnostic(), &hir_map)

src/test/compile-fail/cfg-attr-cfg-2.rs

@@ -8,7 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 //
-// error-pattern: main function not found
+// error-pattern: `main` function not found
 // compile-flags: --cfg foo
 
 // main is conditionally compiled, but the conditional compilation

src/test/compile-fail/cfg-in-crate-1.rs

@@ -8,6 +8,6 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-// error-pattern:main function not found
+// error-pattern: `main` function not found
 
 #![cfg(bar)]

src/test/compile-fail/elided-test.rs

@@ -8,7 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-// error-pattern: main function not found
+// error-pattern: `main` function not found
 
 // Since we're not compiling a test runner this function should be elided
 // and the build will fail because main doesn't exist

src/test/compile-fail/missing-main.rs

@@ -8,5 +8,5 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-// error-pattern:main function not found
+// error-pattern: `main` function not found
 fn mian() { }

src/test/ui/error-codes/E0522.rs

@@ -15,3 +15,5 @@ fn cookie() -> ! {
 //~^^ ERROR definition of an unknown language item: `cookie` [E0522]
     loop {}
 }
+
+fn main() {}

src/test/ui/error-codes/E0522.stderr

@@ -1,12 +1,9 @@
-error[E0601]: main function not found
-
 error[E0522]: definition of an unknown language item: `cookie`
   --> $DIR/E0522.rs:13:1
    |
 LL | #[lang = "cookie"]
    | ^^^^^^^^^^^^^^^^^^ definition of unknown language item `cookie`
 
-error: aborting due to 2 previous errors
+error: aborting due to previous error
 
-Some errors occurred: E0522, E0601.
-For more information about an error, try `rustc --explain E0522`.
+For more information about this error, try `rustc --explain E0522`.

src/test/ui/error-codes/E0601.rs

@@ -0,0 +1,11 @@
+// Copyright 2018 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// Test for main function not found.

src/test/ui/error-codes/E0601.stderr

@@ -0,0 +1,7 @@
+error[E0601]: `main` function not found in crate `E0601`
+   |
+   = note: consider adding a `main` function to `$DIR/E0601.rs`
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0601`.