Rollup merge of #64290 - Mark-Simulacrum:span-no-main, r=estebank

Provide a span if main function is not present in crate

Unfortunately, the diagnostic machinery does not cope well with an empty
span which can happen if the crate is empty, in which case we merely set
a spanless note.

Tests are already updated for this change, so a dedicated test is not added.

Resolves #36561.

42 files changed, 176 insertions, 126 deletions

diff --git a/src/librustc/middle/entry.rs b/src/librustc/middle/entry.rs
index 93bb301f095..ba27d332e43 100644
--- a/src/librustc/middle/entry.rs
+++ b/src/librustc/middle/entry.rs
@@ -16,16 +16,16 @@ struct EntryContext<'a, 'tcx> {
 
     map: &'a hir_map::Map<'tcx>,
 
-    /// The top-level function called 'main'.
+    /// The top-level function called `main`.
     main_fn: Option<(HirId, Span)>,
 
-    /// The function that has attribute named 'main'.
+    /// The function that has attribute named `main`.
     attr_main_fn: Option<(HirId, Span)>,
 
     /// The function that has the attribute 'start' on it.
     start_fn: Option<(HirId, Span)>,
 
-    /// The functions that one might think are 'main' but aren't, e.g.
+    /// The functions that one might think are `main` but aren't, e.g.
     /// main functions not defined at the top level. For diagnostics.
     non_main_fns: Vec<(HirId, Span)> ,
 }
@@ -88,7 +88,7 @@ fn entry_point_type(item: &Item, at_root: bool) -> EntryPointType {
                 EntryPointType::MainAttr
             } else if item.ident.name == sym::main {
                 if at_root {
-                    // This is a top-level function so can be 'main'.
+                    // This is a top-level function so can be `main`.
                     EntryPointType::MainNamed
                 } else {
                     EntryPointType::OtherMain
@@ -109,7 +109,7 @@ fn find_item(item: &Item, ctxt: &mut EntryContext<'_, '_>, at_root: bool) {
                 ctxt.main_fn = Some((item.hir_id, item.span));
             } else {
                 span_err!(ctxt.session, item.span, E0136,
-                          "multiple 'main' functions");
+                          "multiple `main` functions");
             }
         },
         EntryPointType::OtherMain => {
@@ -130,7 +130,7 @@ fn find_item(item: &Item, ctxt: &mut EntryContext<'_, '_>, at_root: bool) {
             if ctxt.start_fn.is_none() {
                 ctxt.start_fn = Some((item.hir_id, item.span));
             } else {
-                struct_span_err!(ctxt.session, item.span, E0138, "multiple 'start' functions")
+                struct_span_err!(ctxt.session, item.span, E0138, "multiple `start` functions")
                     .span_label(ctxt.start_fn.unwrap().1, "previous `start` function here")
                     .span_label(item.span, "multiple `start` functions")
                     .emit();
@@ -148,34 +148,48 @@ fn configure_main(tcx: TyCtxt<'_>, visitor: &EntryContext<'_, '_>) -> Option<(De
     } else if let Some((hir_id, _)) = visitor.main_fn {
         Some((tcx.hir().local_def_id(hir_id), EntryFnType::Main))
     } else {
-        // There is no main function.
-        let mut err = struct_err!(tcx.sess, E0601,
-            "`main` function not found in crate `{}`", tcx.crate_name(LOCAL_CRATE));
-        if !visitor.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 \
-                      but you have one or more functions named 'main' that are not \
-                      defined at the crate level. Either move the definition or \
-                      attach the `#[main]` attribute to override this behavior.");
-            for &(_, span) in &visitor.non_main_fns {
-                err.span_note(span, "here is a function named 'main'");
-            }
-            err.emit();
-        } else {
-            if let Some(ref filename) = tcx.sess.local_crate_source_file {
-                err.note(&format!("consider adding a `main` function to `{}`", filename.display()));
-            }
-            if tcx.sess.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/");
-            }
-            err.emit();
-        }
-
+        no_main_err(tcx, visitor);
         None
     }
 }
 
+fn no_main_err(tcx: TyCtxt<'_>, visitor: &EntryContext<'_, '_>) {
+    // There is no main function.
+    let mut err = struct_err!(tcx.sess, E0601,
+        "`main` function not found in crate `{}`", tcx.crate_name(LOCAL_CRATE));
+    let filename = &tcx.sess.local_crate_source_file;
+    let note = if !visitor.non_main_fns.is_empty() {
+        for &(_, span) in &visitor.non_main_fns {
+            err.span_note(span, "here is a function named `main`");
+        }
+        err.note("you have one or more functions named `main` not defined at the crate level");
+        err.help("either move the `main` function definitions or attach the `#[main]` attribute \
+                  to one of them");
+        // There were some functions named `main` though. Try to give the user a hint.
+        format!("the main function must be defined at the crate level{}",
+                 filename.as_ref().map(|f| format!(" (in `{}`)", f.display())).unwrap_or_default())
+    } else if let Some(filename) = filename {
+        format!("consider adding a `main` function to `{}`", filename.display())
+    } else {
+        String::from("consider adding a `main` function at the crate level")
+    };
+    let sp = tcx.hir().krate().span;
+    // The file may be empty, which leads to the diagnostic machinery not emitting this
+    // note. This is a relatively simple way to detect that case and emit a span-less
+    // note instead.
+    if let Ok(_) = tcx.sess.source_map().lookup_line(sp.lo()) {
+        err.set_span(sp);
+        err.span_label(sp, &note);
+    } else {
+        err.note(&note);
+    }
+    if tcx.sess.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/");
+    }
+    err.emit();
+}
+
 pub fn find_entry_point(tcx: TyCtxt<'_>) -> Option<(DefId, EntryFnType)> {
     tcx.entry_fn(LOCAL_CRATE)
 }
diff --git a/src/test/ui-fulldeps/hash-stable-is-unstable.rs b/src/test/ui-fulldeps/hash-stable-is-unstable.rs
index 9f67f642df1..d79ef62c312 100644
--- a/src/test/ui-fulldeps/hash-stable-is-unstable.rs
+++ b/src/test/ui-fulldeps/hash-stable-is-unstable.rs
@@ -13,3 +13,5 @@ use rustc_macros::HashStable;
 #[derive(HashStable)]
 //~^ use of unstable library feature 'rustc_private'
 struct Test;
+
+fn main() {}
diff --git a/src/test/ui-fulldeps/hash-stable-is-unstable.stderr b/src/test/ui-fulldeps/hash-stable-is-unstable.stderr
index 02056d30eae..e2dc0c3be72 100644
--- a/src/test/ui-fulldeps/hash-stable-is-unstable.stderr
+++ b/src/test/ui-fulldeps/hash-stable-is-unstable.stderr
@@ -1,7 +1,3 @@
-error[E0601]: `main` function not found in crate `hash_stable_is_unstable`
-   |
-   = note: consider adding a `main` function to `$DIR/hash-stable-is-unstable.rs`
-
 error[E0658]: use of unstable library feature 'rustc_private': this crate is being loaded from the sysroot, an unstable location; did you mean to load this crate from crates.io via `Cargo.toml` instead?
   --> $DIR/hash-stable-is-unstable.rs:3:1
    |
@@ -47,7 +43,6 @@ LL | #[derive(HashStable)]
    = note: for more information, see https://github.com/rust-lang/rust/issues/27812
    = help: add `#![feature(rustc_private)]` to the crate attributes to enable
 
-error: aborting due to 6 previous errors
+error: aborting due to 5 previous errors
 
-Some errors have detailed explanations: E0601, E0658.
-For more information about an error, try `rustc --explain E0601`.
+For more information about this error, try `rustc --explain E0658`.
diff --git a/src/test/ui/associated-type-bounds/inside-adt.rs b/src/test/ui/associated-type-bounds/inside-adt.rs
index 83a60825d84..59ce9496d28 100644
--- a/src/test/ui/associated-type-bounds/inside-adt.rs
+++ b/src/test/ui/associated-type-bounds/inside-adt.rs
@@ -31,3 +31,5 @@ union U2 { f: Box<dyn Iterator<Item: Copy>> }
 union U3 { f: dyn Iterator<Item: 'static> }
 //~^ ERROR associated type bounds are not allowed within structs, enums, or unions
 //~| ERROR could not find defining uses
+
+fn main() {}
diff --git a/src/test/ui/associated-type-bounds/inside-adt.stderr b/src/test/ui/associated-type-bounds/inside-adt.stderr
index d0e0ceccd37..9c4d03e9009 100644
--- a/src/test/ui/associated-type-bounds/inside-adt.stderr
+++ b/src/test/ui/associated-type-bounds/inside-adt.stderr
@@ -52,10 +52,6 @@ error: associated type bounds are not allowed within structs, enums, or unions
 LL | union U3 { f: dyn Iterator<Item: 'static> }
    |                            ^^^^^^^^^^^^^
 
-error[E0601]: `main` function not found in crate `inside_adt`
-   |
-   = note: consider adding a `main` function to `$DIR/inside-adt.rs`
-
 error: could not find defining uses
   --> $DIR/inside-adt.rs:5:29
    |
@@ -110,6 +106,5 @@ error: could not find defining uses
 LL | union U3 { f: dyn Iterator<Item: 'static> }
    |                            ^^^^^^^^^^^^^
 
-error: aborting due to 19 previous errors
+error: aborting due to 18 previous errors
 
-For more information about this error, try `rustc --explain E0601`.
diff --git a/src/test/ui/conditional-compilation/cfg-attr-cfg-2.stderr b/src/test/ui/conditional-compilation/cfg-attr-cfg-2.stderr
index db3c7acff15..e9df780def5 100644
--- a/src/test/ui/conditional-compilation/cfg-attr-cfg-2.stderr
+++ b/src/test/ui/conditional-compilation/cfg-attr-cfg-2.stderr
@@ -1,6 +1,9 @@
 error[E0601]: `main` function not found in crate `cfg_attr_cfg_2`
+  --> $DIR/cfg-attr-cfg-2.rs:8:1
    |
-   = note: consider adding a `main` function to `$DIR/cfg-attr-cfg-2.rs`
+LL | / #[cfg_attr(foo, cfg(bar))]
+LL | | fn main() { }
+   | |_____________^ consider adding a `main` function to `$DIR/cfg-attr-cfg-2.rs`
 
 error: aborting due to previous error
 
diff --git a/src/test/ui/conditional-compilation/cfg-in-crate-1.stderr b/src/test/ui/conditional-compilation/cfg-in-crate-1.stderr
index c6d42c732c9..0b5c3e03355 100644
--- a/src/test/ui/conditional-compilation/cfg-in-crate-1.stderr
+++ b/src/test/ui/conditional-compilation/cfg-in-crate-1.stderr
@@ -1,6 +1,8 @@
 error[E0601]: `main` function not found in crate `cfg_in_crate_1`
+  --> $DIR/cfg-in-crate-1.rs:3:1
    |
-   = note: consider adding a `main` function to `$DIR/cfg-in-crate-1.rs`
+LL | #![cfg(bar)]
+   | ^^^^^^^^^^^^ consider adding a `main` function to `$DIR/cfg-in-crate-1.rs`
 
 error: aborting due to previous error
 
diff --git a/src/test/ui/continue-after-missing-main.nll.stderr b/src/test/ui/continue-after-missing-main.nll.stderr
index aceabf33164..b94c365f253 100644
--- a/src/test/ui/continue-after-missing-main.nll.stderr
+++ b/src/test/ui/continue-after-missing-main.nll.stderr
@@ -1,6 +1,14 @@
 error[E0601]: `main` function not found in crate `continue_after_missing_main`
+  --> $DIR/continue-after-missing-main.rs:1:1
    |
-   = note: consider adding a `main` function to `$DIR/continue-after-missing-main.rs`
+LL | / #![allow(dead_code)]
+LL | |
+LL | | // error-pattern:`main` function not found in crate
+LL | |
+...  |
+LL | |
+LL | | }
+   | |_^ consider adding a `main` function to `$DIR/continue-after-missing-main.rs`
 
 error: aborting due to previous error
 
diff --git a/src/test/ui/continue-after-missing-main.stderr b/src/test/ui/continue-after-missing-main.stderr
index cc5f8765907..d764e7d860a 100644
--- a/src/test/ui/continue-after-missing-main.stderr
+++ b/src/test/ui/continue-after-missing-main.stderr
@@ -1,6 +1,14 @@
 error[E0601]: `main` function not found in crate `continue_after_missing_main`
+  --> $DIR/continue-after-missing-main.rs:1:1
    |
-   = note: consider adding a `main` function to `$DIR/continue-after-missing-main.rs`
+LL | / #![allow(dead_code)]
+LL | |
+LL | | // error-pattern:`main` function not found in crate
+LL | |
+...  |
+LL | |
+LL | | }
+   | |_^ consider adding a `main` function to `$DIR/continue-after-missing-main.rs`
 
 error[E0623]: lifetime mismatch
   --> $DIR/continue-after-missing-main.rs:30:56
diff --git a/src/test/ui/elided-test.stderr b/src/test/ui/elided-test.stderr
index d22eee4e8bd..175bd033067 100644
--- a/src/test/ui/elided-test.stderr
+++ b/src/test/ui/elided-test.stderr
@@ -1,6 +1,10 @@
 error[E0601]: `main` function not found in crate `elided_test`
+  --> $DIR/elided-test.rs:5:1
    |
-   = note: consider adding a `main` function to `$DIR/elided-test.rs`
+LL | / #[test]
+LL | | fn main() {
+LL | | }
+   | |_^ consider adding a `main` function to `$DIR/elided-test.rs`
 
 error: aborting due to previous error
 
diff --git a/src/test/ui/error-codes/E0138.stderr b/src/test/ui/error-codes/E0138.stderr
index 745dccfb175..445053a4a89 100644
--- a/src/test/ui/error-codes/E0138.stderr
+++ b/src/test/ui/error-codes/E0138.stderr
@@ -1,4 +1,4 @@
-error[E0138]: multiple 'start' functions
+error[E0138]: multiple `start` functions
   --> $DIR/E0138.rs:7:1
    |
 LL | fn foo(argc: isize, argv: *const *const u8) -> isize { 0 }
diff --git a/src/test/ui/error-codes/E0601.rs b/src/test/ui/error-codes/E0601.rs
index 47feb7f8367..4380ddeac0a 100644
--- a/src/test/ui/error-codes/E0601.rs
+++ b/src/test/ui/error-codes/E0601.rs
@@ -1 +1 @@
-// Test for main function not found.
+//~ ERROR `main` function not found
diff --git a/src/test/ui/error-codes/E0601.stderr b/src/test/ui/error-codes/E0601.stderr
index cbc20db35da..a687f575615 100644
--- a/src/test/ui/error-codes/E0601.stderr
+++ b/src/test/ui/error-codes/E0601.stderr
@@ -1,6 +1,8 @@
 error[E0601]: `main` function not found in crate `E0601`
+  --> $DIR/E0601.rs:1:37
    |
-   = note: consider adding a `main` function to `$DIR/E0601.rs`
+LL |
+   |                                     ^ consider adding a `main` function to `$DIR/E0601.rs`
 
 error: aborting due to previous error
 
diff --git a/src/test/ui/issues/issue-46101.rs b/src/test/ui/issues/issue-46101.rs
index 2d9111e9b3a..8b1343b1326 100644
--- a/src/test/ui/issues/issue-46101.rs
+++ b/src/test/ui/issues/issue-46101.rs
@@ -2,3 +2,5 @@
 trait Foo {}
 #[derive(Foo::Anything)] //~ ERROR failed to resolve: partially resolved path in a derive macro
 struct S;
+
+fn main() {}
diff --git a/src/test/ui/issues/issue-46101.stderr b/src/test/ui/issues/issue-46101.stderr
index 772d4bfeb30..9c88d3b87c9 100644
--- a/src/test/ui/issues/issue-46101.stderr
+++ b/src/test/ui/issues/issue-46101.stderr
@@ -4,11 +4,6 @@ error[E0433]: failed to resolve: partially resolved path in a derive macro
 LL | #[derive(Foo::Anything)]
    |          ^^^^^^^^^^^^^ partially resolved path in a derive macro
 
-error[E0601]: `main` function not found in crate `issue_46101`
-   |
-   = note: consider adding a `main` function to `$DIR/issue-46101.rs`
-
-error: aborting due to 2 previous errors
+error: aborting due to previous error
 
-Some errors have detailed explanations: E0433, E0601.
-For more information about an error, try `rustc --explain E0433`.
+For more information about this error, try `rustc --explain E0433`.
diff --git a/src/test/ui/issues/issue-49040.rs b/src/test/ui/issues/issue-49040.rs
index a5f05d2824e..b7a541dd664 100644
--- a/src/test/ui/issues/issue-49040.rs
+++ b/src/test/ui/issues/issue-49040.rs
@@ -1,2 +1,3 @@
 #![allow(unused_variables)]; //~ ERROR expected item, found `;`
+//~^ ERROR `main` function
 fn foo() {}
diff --git a/src/test/ui/issues/issue-49040.stderr b/src/test/ui/issues/issue-49040.stderr
index de78b8d3c14..4134d6aa544 100644
--- a/src/test/ui/issues/issue-49040.stderr
+++ b/src/test/ui/issues/issue-49040.stderr
@@ -5,8 +5,12 @@ LL | #![allow(unused_variables)];
    |                            ^ help: remove this semicolon
 
 error[E0601]: `main` function not found in crate `issue_49040`
+  --> $DIR/issue-49040.rs:1:1
    |
-   = note: consider adding a `main` function to `$DIR/issue-49040.rs`
+LL | / #![allow(unused_variables)];
+LL | |
+LL | | fn foo() {}
+   | |__^ consider adding a `main` function to `$DIR/issue-49040.rs`
 
 error: aborting due to 2 previous errors
 
diff --git a/src/test/ui/issues/issue-60057.rs b/src/test/ui/issues/issue-60057.rs
index 3027d01c532..b52343adaee 100644
--- a/src/test/ui/issues/issue-60057.rs
+++ b/src/test/ui/issues/issue-60057.rs
@@ -15,3 +15,5 @@ impl A {
         }
     }
 }
+
+fn main() {}
diff --git a/src/test/ui/issues/issue-60057.stderr b/src/test/ui/issues/issue-60057.stderr
index 6b967204ce6..4d915fcd9fe 100644
--- a/src/test/ui/issues/issue-60057.stderr
+++ b/src/test/ui/issues/issue-60057.stderr
@@ -10,11 +10,6 @@ error[E0425]: cannot find value `banana` in this scope
 LL |             banana: banana
    |                     ^^^^^^ help: you might have meant to use the available field: `self.banana`
 
-error[E0601]: `main` function not found in crate `issue_60057`
-   |
-   = note: consider adding a `main` function to `$DIR/issue-60057.rs`
-
-error: aborting due to 3 previous errors
+error: aborting due to 2 previous errors
 
-Some errors have detailed explanations: E0425, E0601.
-For more information about an error, try `rustc --explain E0425`.
+For more information about this error, try `rustc --explain E0425`.
diff --git a/src/test/ui/json-short.stderr b/src/test/ui/json-short.stderr
index dffbdb7e480..86cb2f0a3a8 100644
--- a/src/test/ui/json-short.stderr
+++ b/src/test/ui/json-short.stderr
@@ -11,7 +11,7 @@ fn main() {
 
 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/
-"},"level":"error","spans":[],"children":[{"message":"consider adding a `main` function to `$DIR/json-short.rs`","code":null,"level":"note","spans":[],"children":[],"rendered":null}],"rendered":"error[E0601]: `main` function not found in crate `json_short`
+"},"level":"error","spans":[{"file_name":"$DIR/json-short.rs","byte_start":76,"byte_end":76,"line_start":2,"line_end":2,"column_start":63,"column_end":63,"is_primary":true,"text":[{"text":"// compile-flags: --json=diagnostic-short --error-format=json","highlight_start":63,"highlight_end":63}],"label":"consider adding a `main` function to `$DIR/json-short.rs`","suggested_replacement":null,"suggestion_applicability":null,"expansion":null}],"children":[],"rendered":"$DIR/json-short.rs:2:63: error[E0601]: `main` function not found in crate `json_short`
 "}
 {"message":"aborting due to previous error","code":null,"level":"error","spans":[],"children":[],"rendered":"error: aborting due to previous error
 "}
diff --git a/src/test/ui/lifetime-before-type-params.rs b/src/test/ui/lifetime-before-type-params.rs
index 9b905d4883a..5a71d6efeda 100644
--- a/src/test/ui/lifetime-before-type-params.rs
+++ b/src/test/ui/lifetime-before-type-params.rs
@@ -7,3 +7,5 @@ fn third<T, U, 'a>() {}
 //~^ ERROR lifetime parameters must be declared prior to type parameters
 fn fourth<'a, T, 'b, U, 'c, V>() {}
 //~^ ERROR lifetime parameters must be declared prior to type parameters
+
+fn main() {}
diff --git a/src/test/ui/lifetime-before-type-params.stderr b/src/test/ui/lifetime-before-type-params.stderr
index ffc6784bafe..76d7d0f024d 100644
--- a/src/test/ui/lifetime-before-type-params.stderr
+++ b/src/test/ui/lifetime-before-type-params.stderr
@@ -22,10 +22,5 @@ error: lifetime parameters must be declared prior to type parameters
 LL | fn fourth<'a, T, 'b, U, 'c, V>() {}
    |          --------^^-----^^---- help: reorder the parameters: lifetimes, then types: `<'a, 'b, 'c, T, U, V>`
 
-error[E0601]: `main` function not found in crate `lifetime_before_type_params`
-   |
-   = note: consider adding a `main` function to `$DIR/lifetime-before-type-params.rs`
-
-error: aborting due to 5 previous errors
+error: aborting due to 4 previous errors
 
-For more information about this error, try `rustc --explain E0601`.
diff --git a/src/test/ui/main-wrong-location.rs b/src/test/ui/main-wrong-location.rs
index d7ed5128195..f75d08813cd 100644
--- a/src/test/ui/main-wrong-location.rs
+++ b/src/test/ui/main-wrong-location.rs
@@ -1,4 +1,5 @@
 mod m {
+//~^ ERROR `main` function not found
     // An inferred main entry point (that doesn't use #[main])
     // must appear at the top of the crate
     fn main() { }
diff --git a/src/test/ui/main-wrong-location.stderr b/src/test/ui/main-wrong-location.stderr
index b30931f2f23..e301c2ff09a 100644
--- a/src/test/ui/main-wrong-location.stderr
+++ b/src/test/ui/main-wrong-location.stderr
@@ -1,11 +1,21 @@
 error[E0601]: `main` function not found in crate `main_wrong_location`
+  --> $DIR/main-wrong-location.rs:1:1
    |
-   = note: the main function must be defined at the crate level but you have one or more functions named 'main' that are not defined at the crate level. Either move the definition or attach the `#[main]` attribute to override this behavior.
-note: here is a function named 'main'
-  --> $DIR/main-wrong-location.rs:4:5
+LL | / mod m {
+LL | |
+LL | |     // An inferred main entry point (that doesn't use #[main])
+LL | |     // must appear at the top of the crate
+LL | |     fn main() { }
+LL | | }
+   | |_^ the main function must be defined at the crate level (in `$DIR/main-wrong-location.rs`)
+   |
+note: here is a function named `main`
+  --> $DIR/main-wrong-location.rs:5:5
    |
 LL |     fn main() { }
    |     ^^^^^^^^^^^^^
+   = note: you have one or more functions named `main` not defined at the crate level
+   = help: either move the `main` function definitions or attach the `#[main]` attribute to one of them
 
 error: aborting due to previous error
 
diff --git a/src/test/ui/missing/missing-main.stderr b/src/test/ui/missing/missing-main.stderr
index 34b03ada3d2..6a35f5117ef 100644
--- a/src/test/ui/missing/missing-main.stderr
+++ b/src/test/ui/missing/missing-main.stderr
@@ -1,6 +1,8 @@
 error[E0601]: `main` function not found in crate `missing_main`
+  --> $DIR/missing-main.rs:2:1
    |
-   = note: consider adding a `main` function to `$DIR/missing-main.rs`
+LL | fn mian() { }
+   | ^^^^^^^^^^^^^ consider adding a `main` function to `$DIR/missing-main.rs`
 
 error: aborting due to previous error
 
diff --git a/src/test/ui/parser-recovery-1.rs b/src/test/ui/parser-recovery-1.rs
index 21d36048e67..8126525c34f 100644
--- a/src/test/ui/parser-recovery-1.rs
+++ b/src/test/ui/parser-recovery-1.rs
@@ -3,6 +3,7 @@
 // Test that we can recover from missing braces in the parser.
 
 trait Foo {
+//~^ ERROR `main` function not found
     fn bar() {
         let x = foo();
         //~^ ERROR cannot find function `foo` in this scope
diff --git a/src/test/ui/parser-recovery-1.stderr b/src/test/ui/parser-recovery-1.stderr
index c29f4275917..ffe2b3322fc 100644
--- a/src/test/ui/parser-recovery-1.stderr
+++ b/src/test/ui/parser-recovery-1.stderr
@@ -1,8 +1,9 @@
 error: this file contains an un-closed delimiter
-  --> $DIR/parser-recovery-1.rs:15:55
+  --> $DIR/parser-recovery-1.rs:16:55
    |
 LL | trait Foo {
    |           - un-closed delimiter
+LL |
 LL |     fn bar() {
    |              - this delimiter might not be properly closed...
 ...
@@ -13,26 +14,34 @@ LL | }
    |                                                       ^
 
 error: unexpected token: `;`
-  --> $DIR/parser-recovery-1.rs:12:15
+  --> $DIR/parser-recovery-1.rs:13:15
    |
 LL |     let x = y.;
    |               ^
 
 error[E0425]: cannot find function `foo` in this scope
-  --> $DIR/parser-recovery-1.rs:7:17
+  --> $DIR/parser-recovery-1.rs:8:17
    |
 LL |         let x = foo();
    |                 ^^^ not found in this scope
 
 error[E0425]: cannot find value `y` in this scope
-  --> $DIR/parser-recovery-1.rs:12:13
+  --> $DIR/parser-recovery-1.rs:13:13
    |
 LL |     let x = y.;
    |             ^ not found in this scope
 
 error[E0601]: `main` function not found in crate `parser_recovery_1`
+  --> $DIR/parser-recovery-1.rs:5:1
    |
-   = note: consider adding a `main` function to `$DIR/parser-recovery-1.rs`
+LL | / trait Foo {
+LL | |
+LL | |     fn bar() {
+LL | |         let x = foo();
+...  |
+LL | |
+LL | | }
+   | |______________________________________________________^ consider adding a `main` function to `$DIR/parser-recovery-1.rs`
 
 error: aborting due to 5 previous errors
 
diff --git a/src/test/ui/parser/issue-2354.rs b/src/test/ui/parser/issue-2354.rs
index 565f84822f7..a14eb6e32fc 100644
--- a/src/test/ui/parser/issue-2354.rs
+++ b/src/test/ui/parser/issue-2354.rs
@@ -1,4 +1,7 @@
 fn foo() { //~ NOTE un-closed delimiter
+//~^ ERROR `main` function not found
+//~^^ NOTE main function must be defined
+//~^^^ NOTE you have one or more functions
   match Some(10) {
   //~^ NOTE this delimiter might not be properly closed...
       Some(y) => { panic!(); }
@@ -11,5 +14,5 @@ fn bar() {
     while (i < 1000) {}
 }
 
-fn main() {} //~ NOTE here is a function named 'main'
+fn main() {} //~ NOTE here is a function named `main`
              //~ ERROR this file contains an un-closed delimiter
diff --git a/src/test/ui/parser/issue-2354.stderr b/src/test/ui/parser/issue-2354.stderr
index 7098da738b8..038e3dcfa40 100644
--- a/src/test/ui/parser/issue-2354.stderr
+++ b/src/test/ui/parser/issue-2354.stderr
@@ -1,8 +1,9 @@
 error: this file contains an un-closed delimiter
-  --> $DIR/issue-2354.rs:15:66
+  --> $DIR/issue-2354.rs:18:66
    |
 LL | fn foo() {
    |          - un-closed delimiter
+...
 LL |   match Some(10) {
    |                  - this delimiter might not be properly closed...
 ...
@@ -13,13 +14,24 @@ LL |
    |                                                                  ^
 
 error[E0601]: `main` function not found in crate `issue_2354`
+  --> $DIR/issue-2354.rs:1:1
+   |
+LL | / fn foo() {
+LL | |
+LL | |
+LL | |
+...  |
+LL | | fn main() {}
+LL | |
+   | |_________________________________________________________________^ the main function must be defined at the crate level (in `$DIR/issue-2354.rs`)
    |
-   = note: the main function must be defined at the crate level but you have one or more functions named 'main' that are not defined at the crate level. Either move the definition or attach the `#[main]` attribute to override this behavior.
-note: here is a function named 'main'
-  --> $DIR/issue-2354.rs:14:1
+note: here is a function named `main`
+  --> $DIR/issue-2354.rs:17:1
    |
 LL | fn main() {}
    | ^^^^^^^^^^^^
+   = note: you have one or more functions named `main` not defined at the crate level
+   = help: either move the `main` function definitions or attach the `#[main]` attribute to one of them
 
 error: aborting due to 2 previous errors
 
diff --git a/src/test/ui/parser/lex-bad-char-literals-2.rs b/src/test/ui/parser/lex-bad-char-literals-2.rs
index 1e180f87fc1..d35dafd9a34 100644
--- a/src/test/ui/parser/lex-bad-char-literals-2.rs
+++ b/src/test/ui/parser/lex-bad-char-literals-2.rs
@@ -2,3 +2,5 @@
 static c: char =
     'nope' //~ ERROR: character literal may only contain one codepoint
 ;
+
+fn main() {}
diff --git a/src/test/ui/parser/lex-bad-char-literals-2.stderr b/src/test/ui/parser/lex-bad-char-literals-2.stderr
index b0a4ed02434..5653d4ea672 100644
--- a/src/test/ui/parser/lex-bad-char-literals-2.stderr
+++ b/src/test/ui/parser/lex-bad-char-literals-2.stderr
@@ -8,10 +8,5 @@ help: if you meant to write a `str` literal, use double quotes
 LL |     "nope"
    |     ^^^^^^
 
-error[E0601]: `main` function not found in crate `lex_bad_char_literals_2`
-   |
-   = note: consider adding a `main` function to `$DIR/lex-bad-char-literals-2.rs`
-
-error: aborting due to 2 previous errors
+error: aborting due to previous error
 
-For more information about this error, try `rustc --explain E0601`.
diff --git a/src/test/ui/parser/unclosed-delimiter-in-dep.stderr b/src/test/ui/parser/unclosed-delimiter-in-dep.stderr
index 633c63bea91..818f61b4d22 100644
--- a/src/test/ui/parser/unclosed-delimiter-in-dep.stderr
+++ b/src/test/ui/parser/unclosed-delimiter-in-dep.stderr
@@ -1,5 +1,5 @@
 error: incorrect close delimiter: `}`
-  --> $DIR/unclosed_delim_mod.rs:5:1
+  --> $DIR/unclosed_delim_mod.rs:7:1
    |
 LL | pub fn new() -> Result<Value, ()> {
    |                                   - close delimiter possibly meant for this
diff --git a/src/test/ui/parser/unclosed_delim_mod.rs b/src/test/ui/parser/unclosed_delim_mod.rs
index b1664f49dc5..486e2331281 100644
--- a/src/test/ui/parser/unclosed_delim_mod.rs
+++ b/src/test/ui/parser/unclosed_delim_mod.rs
@@ -1,3 +1,5 @@
+fn main() {}
+
 pub struct Value {}
 pub fn new() -> Result<Value, ()> {
     Ok(Value {
diff --git a/src/test/ui/parser/unclosed_delim_mod.stderr b/src/test/ui/parser/unclosed_delim_mod.stderr
index cc04eb531cb..fe2d968af0f 100644
--- a/src/test/ui/parser/unclosed_delim_mod.stderr
+++ b/src/test/ui/parser/unclosed_delim_mod.stderr
@@ -1,5 +1,5 @@
 error: incorrect close delimiter: `}`
-  --> $DIR/unclosed_delim_mod.rs:5:1
+  --> $DIR/unclosed_delim_mod.rs:7:1
    |
 LL | pub fn new() -> Result<Value, ()> {
    |                                   - close delimiter possibly meant for this
@@ -9,10 +9,5 @@ LL |     }
 LL | }
    | ^ incorrect close delimiter
 
-error[E0601]: `main` function not found in crate `unclosed_delim_mod`
-   |
-   = note: consider adding a `main` function to `$DIR/unclosed_delim_mod.rs`
-
-error: aborting due to 2 previous errors
+error: aborting due to previous error
 
-For more information about this error, try `rustc --explain E0601`.
diff --git a/src/test/ui/resolve/visibility-indeterminate.rs b/src/test/ui/resolve/visibility-indeterminate.rs
index 595eaf440c9..198ea752881 100644
--- a/src/test/ui/resolve/visibility-indeterminate.rs
+++ b/src/test/ui/resolve/visibility-indeterminate.rs
@@ -3,3 +3,5 @@
 foo!(); //~ ERROR cannot find macro `foo!` in this scope
 
 pub(in ::bar) struct Baz {} //~ ERROR cannot determine resolution for the visibility
+
+fn main() {}
diff --git a/src/test/ui/resolve/visibility-indeterminate.stderr b/src/test/ui/resolve/visibility-indeterminate.stderr
index a259c8090b3..17927a5967d 100644
--- a/src/test/ui/resolve/visibility-indeterminate.stderr
+++ b/src/test/ui/resolve/visibility-indeterminate.stderr
@@ -10,10 +10,5 @@ error: cannot find macro `foo!` in this scope
 LL | foo!();
    | ^^^
 
-error[E0601]: `main` function not found in crate `visibility_indeterminate`
-   |
-   = note: consider adding a `main` function to `$DIR/visibility-indeterminate.rs`
-
-error: aborting due to 3 previous errors
+error: aborting due to 2 previous errors
 
-For more information about this error, try `rustc --explain E0601`.
diff --git a/src/test/ui/tool-attributes/diagnostic_item.rs b/src/test/ui/tool-attributes/diagnostic_item.rs
index 1d35422ed62..26a52ce60cf 100644
--- a/src/test/ui/tool-attributes/diagnostic_item.rs
+++ b/src/test/ui/tool-attributes/diagnostic_item.rs
@@ -1,2 +1,3 @@
 #[rustc_diagnostic_item = "foomp"] //~ ERROR compiler internal support for linting
 struct Foomp;
+fn main() {}
diff --git a/src/test/ui/tool-attributes/diagnostic_item.stderr b/src/test/ui/tool-attributes/diagnostic_item.stderr
index deff4da6b80..5432f8dea86 100644
--- a/src/test/ui/tool-attributes/diagnostic_item.stderr
+++ b/src/test/ui/tool-attributes/diagnostic_item.stderr
@@ -7,11 +7,6 @@ LL | #[rustc_diagnostic_item = "foomp"]
    = note: for more information, see https://github.com/rust-lang/rust/issues/29642
    = help: add `#![feature(rustc_attrs)]` to the crate attributes to enable
 
-error[E0601]: `main` function not found in crate `diagnostic_item`
-   |
-   = note: consider adding a `main` function to `$DIR/diagnostic_item.rs`
-
-error: aborting due to 2 previous errors
+error: aborting due to previous error
 
-Some errors have detailed explanations: E0601, E0658.
-For more information about an error, try `rustc --explain E0601`.
+For more information about this error, try `rustc --explain E0658`.
diff --git a/src/test/ui/type-alias-impl-trait/issue-60564.rs b/src/test/ui/type-alias-impl-trait/issue-60564.rs
index 91c4576597e..9e96b1cf7b0 100644
--- a/src/test/ui/type-alias-impl-trait/issue-60564.rs
+++ b/src/test/ui/type-alias-impl-trait/issue-60564.rs
@@ -24,3 +24,5 @@ where
             .map(move |shift| ((self >> T::from(shift)) & T::from(1)).try_into().unwrap())
     }
 }
+
+fn main() {}
diff --git a/src/test/ui/type-alias-impl-trait/issue-60564.stderr b/src/test/ui/type-alias-impl-trait/issue-60564.stderr
index ebb13fca1da..b838c06cade 100644
--- a/src/test/ui/type-alias-impl-trait/issue-60564.stderr
+++ b/src/test/ui/type-alias-impl-trait/issue-60564.stderr
@@ -1,7 +1,3 @@
-error[E0601]: `main` function not found in crate `issue_60564`
-   |
-   = note: consider adding a `main` function to `$DIR/issue-60564.rs`
-
 error: type parameter `E` is part of concrete type but not used in parameter list for the `impl Trait` type alias
   --> $DIR/issue-60564.rs:20:49
    |
@@ -20,6 +16,5 @@ error: could not find defining uses
 LL | type IterBitsIter<T, E, I> = impl std::iter::Iterator<Item = I>;
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
-error: aborting due to 3 previous errors
+error: aborting due to 2 previous errors
 
-For more information about this error, try `rustc --explain E0601`.
diff --git a/src/test/ui/type/ascription/issue-34255-1.rs b/src/test/ui/type/ascription/issue-34255-1.rs
index c11a248d3c7..c21d9f3d97c 100644
--- a/src/test/ui/type/ascription/issue-34255-1.rs
+++ b/src/test/ui/type/ascription/issue-34255-1.rs
@@ -13,3 +13,4 @@ impl Reactor {
 }
 
 // This case isn't currently being handled gracefully, including for completeness.
+fn main() {}
diff --git a/src/test/ui/type/ascription/issue-34255-1.stderr b/src/test/ui/type/ascription/issue-34255-1.stderr
index 531455b82b4..195b393b2f6 100644
--- a/src/test/ui/type/ascription/issue-34255-1.stderr
+++ b/src/test/ui/type/ascription/issue-34255-1.stderr
@@ -14,17 +14,13 @@ LL |         input_cells: Vec::new()
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
    = note: for more information, see issue #42238 <https://github.com/rust-lang/rust/issues/42238>
 
-error[E0601]: `main` function not found in crate `issue_34255_1`
-   |
-   = note: consider adding a `main` function to `$DIR/issue-34255-1.rs`
-
 error[E0107]: wrong number of type arguments: expected 1, found 0
   --> $DIR/issue-34255-1.rs:7:22
    |
 LL |         input_cells: Vec::new()
    |                      ^^^^^^^^^^ expected 1 type argument
 
-error: aborting due to 4 previous errors
+error: aborting due to 3 previous errors
 
-Some errors have detailed explanations: E0107, E0425, E0601.
+Some errors have detailed explanations: E0107, E0425.
 For more information about an error, try `rustc --explain E0107`.