From fc83a0cb57eaad7104cc8861ba354fc76da79684 Mon Sep 17 00:00:00 2001
From: Luqman Aden <me@luqman.ca>
Date: Sun, 7 Aug 2022 04:03:28 -0700
Subject: [PATCH 1/2] Don't ICE while suggesting updating item path.

When an item isn't found, we may suggest an appropriate import to
`use`. Along with that, we also suggest updating the path to work
with the `use`. Unfortunately, if the code in question originates
from a macro, the span used to indicate which part of the path
needs updating may not be suitable and cause an ICE. Since, such
code is not adjustable directly by the user without modifying the
macro, just skip the suggestion in such cases.
---
 compiler/rustc_resolve/src/diagnostics.rs | 15 +++++++++------
 1 file changed, 9 insertions(+), 6 deletions(-)

diff --git a/compiler/rustc_resolve/src/diagnostics.rs b/compiler/rustc_resolve/src/diagnostics.rs
index 8839fb1a151..325b0458638 100644
--- a/compiler/rustc_resolve/src/diagnostics.rs
+++ b/compiler/rustc_resolve/src/diagnostics.rs
@@ -2544,12 +2544,15 @@ fn show_candidates(
                 Applicability::MaybeIncorrect,
             );
             if let [first, .., last] = &path[..] {
-                err.span_suggestion_verbose(
-                    first.ident.span.until(last.ident.span),
-                    &format!("if you import `{}`, refer to it directly", last.ident),
-                    "",
-                    Applicability::Unspecified,
-                );
+                let sp = first.ident.span.until(last.ident.span);
+                if sp.can_be_used_for_suggestions() {
+                    err.span_suggestion_verbose(
+                        sp,
+                        &format!("if you import `{}`, refer to it directly", last.ident),
+                        "",
+                        Applicability::Unspecified,
+                    );
+                }
             }
         } else {
             msg.push(':');

From 15b1daaca3fd4020d7a93cff14507b9104ec6d02 Mon Sep 17 00:00:00 2001
From: Luqman Aden <me@luqman.ca>
Date: Sun, 7 Aug 2022 13:55:36 -0700
Subject: [PATCH 2/2] Add UI test for #100199

---
 src/test/ui/macros/auxiliary/issue-100199.rs | 18 ++++++++++++++++++
 src/test/ui/macros/issue-100199.rs           | 16 ++++++++++++++++
 src/test/ui/macros/issue-100199.stderr       | 15 +++++++++++++++
 3 files changed, 49 insertions(+)
 create mode 100644 src/test/ui/macros/auxiliary/issue-100199.rs
 create mode 100644 src/test/ui/macros/issue-100199.rs
 create mode 100644 src/test/ui/macros/issue-100199.stderr

diff --git a/src/test/ui/macros/auxiliary/issue-100199.rs b/src/test/ui/macros/auxiliary/issue-100199.rs
new file mode 100644
index 00000000000..9e190b542db
--- /dev/null
+++ b/src/test/ui/macros/auxiliary/issue-100199.rs
@@ -0,0 +1,18 @@
+// force-host
+// no-prefer-dynamic
+
+#![crate_type = "proc-macro"]
+#![feature(proc_macro_quote)]
+
+extern crate proc_macro;
+
+use proc_macro::{quote, Ident, Span, TokenStream, TokenTree};
+
+#[proc_macro_attribute]
+pub fn struct_with_bound(_: TokenStream, _: TokenStream) -> TokenStream {
+    let crate_ident = TokenTree::Ident(Ident::new("crate", Span::call_site()));
+    let trait_ident = TokenTree::Ident(Ident::new("MyTrait", Span::call_site()));
+    quote!(
+        struct Foo<T: $crate_ident::$trait_ident> {}
+    )
+}
diff --git a/src/test/ui/macros/issue-100199.rs b/src/test/ui/macros/issue-100199.rs
new file mode 100644
index 00000000000..6e50afa0759
--- /dev/null
+++ b/src/test/ui/macros/issue-100199.rs
@@ -0,0 +1,16 @@
+#[issue_100199::struct_with_bound] //~ ERROR cannot find trait `MyTrait` in the crate root
+struct Foo {}
+// The above must be on the first line so that it's span points to pos 0.
+// This used to trigger an ICE because the diagnostic emitter would get
+// an unexpected dummy span (lo == 0 == hi) while attempting to print a
+// suggestion.
+
+// aux-build: issue-100199.rs
+
+extern crate issue_100199;
+
+mod traits {
+    pub trait MyTrait {}
+}
+
+fn main() {}
diff --git a/src/test/ui/macros/issue-100199.stderr b/src/test/ui/macros/issue-100199.stderr
new file mode 100644
index 00000000000..2cb45dc1247
--- /dev/null
+++ b/src/test/ui/macros/issue-100199.stderr
@@ -0,0 +1,15 @@
+error[E0405]: cannot find trait `MyTrait` in the crate root
+  --> $DIR/issue-100199.rs:1:1
+   |
+LL | #[issue_100199::struct_with_bound]
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ not found in the crate root
+   |
+   = note: this error originates in the attribute macro `issue_100199::struct_with_bound` (in Nightly builds, run with -Z macro-backtrace for more info)
+help: consider importing this trait
+   |
+LL | use traits::MyTrait;
+   |
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0405`.