1 files changed, 88 insertions, 0 deletions
diff --git a/third_party/rust/thiserror/tests/test_expr.rs b/third_party/rust/thiserror/tests/test_expr.rs
new file mode 100644
index 0000000000..34de56087b
--- /dev/null
+++ b/third_party/rust/thiserror/tests/test_expr.rs
@@ -0,0 +1,88 @@
+#![allow(clippy::iter_cloned_collect, clippy::option_if_let_else)]
+
+use std::fmt::Display;
+use thiserror::Error;
+
+// Some of the elaborate cases from the rcc codebase, which is a C compiler in
+// Rust. https://github.com/jyn514/rcc/blob/0.8.0/src/data/error.rs
+#[derive(Error, Debug)]
+pub enum CompilerError {
+    #[error("cannot shift {} by {maximum} or more bits (got {current})", if *.is_left { "left" } else { "right" })]
+    TooManyShiftBits {
+        is_left: bool,
+        maximum: u64,
+        current: u64,
+    },
+
+    #[error("#error {}", (.0).iter().copied().collect::<Vec<_>>().join(" "))]
+    User(Vec<&'static str>),
+
+    #[error("overflow while parsing {}integer literal",
+        if let Some(signed) = .is_signed {
+            if *signed { "signed "} else { "unsigned "}
+        } else {
+            ""
+        }
+    )]
+    IntegerOverflow { is_signed: Option<bool> },
+
+    #[error("overflow while parsing {}integer literal", match .is_signed {
+        Some(true) => "signed ",
+        Some(false) => "unsigned ",
+        None => "",
+    })]
+    IntegerOverflow2 { is_signed: Option<bool> },
+}
+
+// Examples drawn from Rustup.
+#[derive(Error, Debug)]
+pub enum RustupError {
+    #[error(
+        "toolchain '{name}' does not contain component {component}{}",
+        .suggestion
+            .as_ref()
+            .map_or_else(String::new, |s| format!("; did you mean '{}'?", s)),
+    )]
+    UnknownComponent {
+        name: String,
+        component: String,
+        suggestion: Option<String>,
+    },
+}
+
+fn assert<T: Display>(expected: &str, value: T) {
+    assert_eq!(expected, value.to_string());
+}
+
+#[test]
+fn test_rcc() {
+    assert(
+        "cannot shift left by 32 or more bits (got 50)",
+        CompilerError::TooManyShiftBits {
+            is_left: true,
+            maximum: 32,
+            current: 50,
+        },
+    );
+
+    assert("#error A B C", CompilerError::User(vec!["A", "B", "C"]));
+
+    assert(
+        "overflow while parsing signed integer literal",
+        CompilerError::IntegerOverflow {
+            is_signed: Some(true),
+        },
+    );
+}
+
+#[test]
+fn test_rustup() {
+    assert(
+        "toolchain 'nightly' does not contain component clipy; did you mean 'clippy'?",
+        RustupError::UnknownComponent {
+            name: "nightly".to_owned(),
+            component: "clipy".to_owned(),
+            suggestion: Some("clippy".to_owned()),
+        },
+    );
+}