From e645cca90555cbef9581a86eb7eaa1a4ac6d7c46 Mon Sep 17 00:00:00 2001
From: Ferdia McKeogh <ferdia@mckeogh.tech>
Date: Mon, 13 Jul 2020 13:54:18 +0100
Subject: [PATCH] Add note and suggestion when crate location fails due to the
 identifier `meta` being used

---
 src/librustc_metadata/locator.rs                | 10 +++++++++-
 .../rfc-2126-extern-absolute-paths/meta.stderr  |  6 ++++++
 .../issue-73948-meta-as-module-name.fixed       | 17 +++++++++++++++++
 .../issue-73948-meta-as-module-name.rs          | 17 +++++++++++++++++
 .../issue-73948-meta-as-module-name.stderr      | 15 +++++++++++++++
 5 files changed, 64 insertions(+), 1 deletion(-)
 create mode 100644 src/test/ui/suggestions/issue-73948-meta-as-module-name.fixed
 create mode 100644 src/test/ui/suggestions/issue-73948-meta-as-module-name.rs
 create mode 100644 src/test/ui/suggestions/issue-73948-meta-as-module-name.stderr

diff --git a/src/librustc_metadata/locator.rs b/src/librustc_metadata/locator.rs
index 8828b318d1ea6..06abcc3aec5de 100644
--- a/src/librustc_metadata/locator.rs
+++ b/src/librustc_metadata/locator.rs
@@ -219,7 +219,7 @@ use rustc_data_structures::fx::{FxHashMap, FxHashSet};
 use rustc_data_structures::owning_ref::OwningRef;
 use rustc_data_structures::svh::Svh;
 use rustc_data_structures::sync::MetadataRef;
-use rustc_errors::struct_span_err;
+use rustc_errors::{struct_span_err, Applicability};
 use rustc_middle::middle::cstore::{CrateSource, MetadataLoader};
 use rustc_session::config::{self, CrateType};
 use rustc_session::filesearch::{FileDoesntMatch, FileMatches, FileSearch};
@@ -1068,6 +1068,14 @@ impl CrateError {
                         err.note(&format!("the `{}` target may not be installed", locator.triple));
                     } else if crate_name == sym::profiler_builtins {
                         err.note(&"the compiler may have been built without the profiler runtime");
+                    } else if crate_name == sym::meta {
+                        err.note(&"meta is a reserved crate name");
+                        err.span_suggestion(
+                                span,
+                                "you can use `crate::` or `self::` if you intended to refer to a local module and not a crate",
+                                "crate::meta".to_string(),
+                                Applicability::MaybeIncorrect,
+                            );
                     }
                     err.span_label(span, "can't find crate");
                     err
diff --git a/src/test/ui/rfc-2126-extern-absolute-paths/meta.stderr b/src/test/ui/rfc-2126-extern-absolute-paths/meta.stderr
index eb4b9dea41bdd..105f4b717455e 100644
--- a/src/test/ui/rfc-2126-extern-absolute-paths/meta.stderr
+++ b/src/test/ui/rfc-2126-extern-absolute-paths/meta.stderr
@@ -3,6 +3,12 @@ error[E0463]: can't find crate for `meta`
    |
 LL | use meta;
    |     ^^^^ can't find crate
+   |
+   = note: meta is a reserved crate name
+help: you can use `crate::` or `self::` if you intended to refer to a local module and not a crate
+   |
+LL | use crate::meta;
+   |     ^^^^^^^^^^^
 
 error: aborting due to previous error
 
diff --git a/src/test/ui/suggestions/issue-73948-meta-as-module-name.fixed b/src/test/ui/suggestions/issue-73948-meta-as-module-name.fixed
new file mode 100644
index 0000000000000..9577dba495b2b
--- /dev/null
+++ b/src/test/ui/suggestions/issue-73948-meta-as-module-name.fixed
@@ -0,0 +1,17 @@
+// check-only
+// run-rustfix
+// edition:2018
+
+// https://github.com/rust-lang/rust/issues/73948
+// Tests that when `meta` is used as a module name and imported uniformly a
+// suggestion is made to make the import unambiguous with `crate::meta`
+
+mod meta {
+    pub const FOO: bool = true;
+}
+
+use crate::meta::FOO; //~ ERROR can't find crate for `meta`
+
+fn main() {
+    assert!(FOO);
+}
diff --git a/src/test/ui/suggestions/issue-73948-meta-as-module-name.rs b/src/test/ui/suggestions/issue-73948-meta-as-module-name.rs
new file mode 100644
index 0000000000000..98b8f66bd76e0
--- /dev/null
+++ b/src/test/ui/suggestions/issue-73948-meta-as-module-name.rs
@@ -0,0 +1,17 @@
+// check-only
+// run-rustfix
+// edition:2018
+
+// https://github.com/rust-lang/rust/issues/73948
+// Tests that when `meta` is used as a module name and imported uniformly a
+// suggestion is made to make the import unambiguous with `crate::meta`
+
+mod meta {
+    pub const FOO: bool = true;
+}
+
+use meta::FOO; //~ ERROR can't find crate for `meta`
+
+fn main() {
+    assert!(FOO);
+}
diff --git a/src/test/ui/suggestions/issue-73948-meta-as-module-name.stderr b/src/test/ui/suggestions/issue-73948-meta-as-module-name.stderr
new file mode 100644
index 0000000000000..01fecb8e873b0
--- /dev/null
+++ b/src/test/ui/suggestions/issue-73948-meta-as-module-name.stderr
@@ -0,0 +1,15 @@
+error[E0463]: can't find crate for `meta`
+  --> $DIR/issue-73948-meta-as-module-name.rs:13:5
+   |
+LL | use meta::FOO;
+   |     ^^^^ can't find crate
+   |
+   = note: meta is a reserved crate name
+help: you can use `crate::` or `self::` if you intended to refer to a local module and not a crate
+   |
+LL | use crate::meta::FOO;
+   |     ^^^^^^^^^^^
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0463`.