From c7f1b977ed807d987da0350133b1443fd2caa21f Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Esteban=20K=C3=BCber?= <esteban@kuber.com.ar>
Date: Wed, 12 Dec 2018 16:54:27 -0800
Subject: [PATCH 1/2] Suggest using `.display()` when trying to print a `Path`

---
 src/libcore/fmt/mod.rs                      |  9 +++++++--
 src/test/ui/suggestions/path-display.rs     |  7 +++++++
 src/test/ui/suggestions/path-display.stderr | 14 ++++++++++++++
 3 files changed, 28 insertions(+), 2 deletions(-)
 create mode 100644 src/test/ui/suggestions/path-display.rs
 create mode 100644 src/test/ui/suggestions/path-display.stderr

diff --git a/src/libcore/fmt/mod.rs b/src/libcore/fmt/mod.rs
index 0c5256b981e5c..de93651569891 100644
--- a/src/libcore/fmt/mod.rs
+++ b/src/libcore/fmt/mod.rs
@@ -609,10 +609,15 @@ pub trait Debug {
 /// println!("The origin is: {}", origin);
 /// ```
 #[rustc_on_unimplemented(
+    on(
+        _Self="std::path::Path",
+        label="`{Self}` cannot be formatted with the default formatter, call `.display()` on it",
+        note="you need to call `.display()` or `.to_string_lossy()` for safely printing paths as \
+              they may contain non-Unicode data"
+    ),
     message="`{Self}` doesn't implement `{Display}`",
     label="`{Self}` cannot be formatted with the default formatter",
-    note="in format strings you may be able to use `{{:?}}` \
-          (or {{:#?}} for pretty-print) instead",
+    note="in format strings you may be able to use `{{:?}}` (or {{:#?}} for pretty-print) instead",
 )]
 #[doc(alias = "{}")]
 #[stable(feature = "rust1", since = "1.0.0")]
diff --git a/src/test/ui/suggestions/path-display.rs b/src/test/ui/suggestions/path-display.rs
new file mode 100644
index 0000000000000..62fc9e79f7aa2
--- /dev/null
+++ b/src/test/ui/suggestions/path-display.rs
@@ -0,0 +1,7 @@
+use std::path::Path;
+
+fn main() {
+    let path = Path::new("/tmp/foo/bar.txt");
+    println!("{}", path);
+    //~^ ERROR E0277
+}
diff --git a/src/test/ui/suggestions/path-display.stderr b/src/test/ui/suggestions/path-display.stderr
new file mode 100644
index 0000000000000..b0493a559f92e
--- /dev/null
+++ b/src/test/ui/suggestions/path-display.stderr
@@ -0,0 +1,14 @@
+error[E0277]: `std::path::Path` doesn't implement `std::fmt::Display`
+  --> $DIR/path-display.rs:5:20
+   |
+LL |     println!("{}", path);
+   |                    ^^^^ `std::path::Path` cannot be formatted with the default formatter, call `.display()` on it
+   |
+   = help: the trait `std::fmt::Display` is not implemented for `std::path::Path`
+   = note: you need to call `.display()` or `.to_string_lossy()` for safely printing paths as they may contain non-Unicode data
+   = note: required because of the requirements on the impl of `std::fmt::Display` for `&std::path::Path`
+   = note: required by `std::fmt::Display::fmt`
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0277`.

From 33a34b06ac8828ffddc91b822fdec9f862658600 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Esteban=20K=C3=BCber?= <esteban@kuber.com.ar>
Date: Thu, 13 Dec 2018 09:55:16 -0800
Subject: [PATCH 2/2] Wording changes

---
 src/libcore/fmt/mod.rs                      | 6 +++---
 src/test/ui/suggestions/path-display.stderr | 4 ++--
 2 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/src/libcore/fmt/mod.rs b/src/libcore/fmt/mod.rs
index de93651569891..8e0caa5ae330d 100644
--- a/src/libcore/fmt/mod.rs
+++ b/src/libcore/fmt/mod.rs
@@ -611,9 +611,9 @@ pub trait Debug {
 #[rustc_on_unimplemented(
     on(
         _Self="std::path::Path",
-        label="`{Self}` cannot be formatted with the default formatter, call `.display()` on it",
-        note="you need to call `.display()` or `.to_string_lossy()` for safely printing paths as \
-              they may contain non-Unicode data"
+        label="`{Self}` cannot be formatted with the default formatter; call `.display()` on it",
+        note="call `.display()` or `.to_string_lossy()` to safely print paths, \
+              as they may contain non-Unicode data"
     ),
     message="`{Self}` doesn't implement `{Display}`",
     label="`{Self}` cannot be formatted with the default formatter",
diff --git a/src/test/ui/suggestions/path-display.stderr b/src/test/ui/suggestions/path-display.stderr
index b0493a559f92e..39d236af4f3ae 100644
--- a/src/test/ui/suggestions/path-display.stderr
+++ b/src/test/ui/suggestions/path-display.stderr
@@ -2,10 +2,10 @@ error[E0277]: `std::path::Path` doesn't implement `std::fmt::Display`
   --> $DIR/path-display.rs:5:20
    |
 LL |     println!("{}", path);
-   |                    ^^^^ `std::path::Path` cannot be formatted with the default formatter, call `.display()` on it
+   |                    ^^^^ `std::path::Path` cannot be formatted with the default formatter; call `.display()` on it
    |
    = help: the trait `std::fmt::Display` is not implemented for `std::path::Path`
-   = note: you need to call `.display()` or `.to_string_lossy()` for safely printing paths as they may contain non-Unicode data
+   = note: call `.display()` or `.to_string_lossy()` to safely print paths, as they may contain non-Unicode data
    = note: required because of the requirements on the impl of `std::fmt::Display` for `&std::path::Path`
    = note: required by `std::fmt::Display::fmt`