From d19bdf9b48bdf520ad83cfa2af148a6b1ee8ab26 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?R=C3=A9my=20Rakic?= <remy.rakic+github@gmail.com>
Date: Sun, 12 Jan 2025 08:05:50 +0000
Subject: [PATCH 1/2] add test for `string_enum`

---
 src/tools/compiletest/src/common.rs |  4 ++++
 src/tools/compiletest/src/tests.rs  | 27 +++++++++++++++++++++++++++
 2 files changed, 31 insertions(+)

diff --git a/src/tools/compiletest/src/common.rs b/src/tools/compiletest/src/common.rs
index 36f876bcdc604..8c4a89baa0081 100644
--- a/src/tools/compiletest/src/common.rs
+++ b/src/tools/compiletest/src/common.rs
@@ -51,6 +51,10 @@ macro_rules! string_enum {
     }
 }
 
+// Make the macro visible outside of this module, for tests.
+#[cfg(test)]
+pub(crate) use string_enum;
+
 string_enum! {
     #[derive(Clone, Copy, PartialEq, Debug)]
     pub enum Mode {
diff --git a/src/tools/compiletest/src/tests.rs b/src/tools/compiletest/src/tests.rs
index fec746904dedf..f8a74528101b7 100644
--- a/src/tools/compiletest/src/tests.rs
+++ b/src/tools/compiletest/src/tests.rs
@@ -66,3 +66,30 @@ fn is_test_test() {
     assert!(!is_test(&OsString::from("#a_dog_gif")));
     assert!(!is_test(&OsString::from("~a_temp_file")));
 }
+
+#[test]
+fn string_enums() {
+    // These imports are needed for the macro-generated code
+    use std::fmt;
+    use std::str::FromStr;
+
+    crate::common::string_enum! {
+        #[derive(Clone, Copy, Debug, PartialEq)]
+        enum Animal {
+            Cat => "meow",
+            Dog => "woof",
+        }
+    }
+
+    // General assertions, mostly to silence the dead code warnings
+    assert_eq!(Animal::VARIANTS.len(), 2);
+    assert_eq!(Animal::STR_VARIANTS.len(), 2);
+
+    // Correct string conversions
+    assert_eq!(Animal::Cat, "meow".parse().unwrap());
+    assert_eq!(Animal::Dog, "woof".parse().unwrap());
+
+    // Invalid conversions
+    let animal = "nya".parse::<Animal>();
+    assert!(matches!(animal, Err(())));
+}

From 33ce74f308ac0d849b9cd4d88f3ebdb4238be18a Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?R=C3=A9my=20Rakic?= <remy.rakic+github@gmail.com>
Date: Sun, 12 Jan 2025 08:13:45 +0000
Subject: [PATCH 2/2] add error message to `string_enum!`s string conversions

---
 src/tools/compiletest/src/common.rs | 6 +++---
 src/tools/compiletest/src/tests.rs  | 2 +-
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/src/tools/compiletest/src/common.rs b/src/tools/compiletest/src/common.rs
index 8c4a89baa0081..4e2510ed9aba3 100644
--- a/src/tools/compiletest/src/common.rs
+++ b/src/tools/compiletest/src/common.rs
@@ -39,12 +39,12 @@ macro_rules! string_enum {
         }
 
         impl FromStr for $name {
-            type Err = ();
+            type Err = String;
 
-            fn from_str(s: &str) -> Result<Self, ()> {
+            fn from_str(s: &str) -> Result<Self, Self::Err> {
                 match s {
                     $($repr => Ok(Self::$variant),)*
-                    _ => Err(()),
+                    _ => Err(format!(concat!("unknown `", stringify!($name), "` variant: `{}`"), s)),
                 }
             }
         }
diff --git a/src/tools/compiletest/src/tests.rs b/src/tools/compiletest/src/tests.rs
index f8a74528101b7..43c6dc0a67e89 100644
--- a/src/tools/compiletest/src/tests.rs
+++ b/src/tools/compiletest/src/tests.rs
@@ -91,5 +91,5 @@ fn string_enums() {
 
     // Invalid conversions
     let animal = "nya".parse::<Animal>();
-    assert!(matches!(animal, Err(())));
+    assert_eq!("unknown `Animal` variant: `nya`", animal.unwrap_err());
 }