Fix display impl for empty enum and non provided enum (#11)

* Add no_display attribute
* Add tests with trybuild
* Fix doc

Cargo.toml

@@ -17,8 +17,14 @@ std = []
 [lib]
 proc-macro = true
 
+[[test]]
+name = "compile_and_fail"
+path = "compile_tests/compiler.rs"
+
 [dependencies]
 myn = "0.1"
 
 [dev-dependencies]
 error-iter = "0.4"
+rustversion = "1.0.12"
+trybuild = "1.0.80"

compile_tests/compiler.rs

@@ -0,0 +1,15 @@
+#[test]
+fn compile_tests() {
+    let t = trybuild::TestCases::new();
+    t.pass("compile_tests/empty.rs");
+    t.pass("compile_tests/one_comment.rs");
+    t.pass("compile_tests/one_param.rs");
+    t.compile_fail("compile_tests/one_non_signed.rs");
+    t.pass("compile_tests/multiple_variant.rs");
+    t.compile_fail("compile_tests/multiple_non_signed.rs");
+    t.compile_fail("compile_tests/multiple_one_non_signed.rs");
+    t.pass("compile_tests/no_display.rs");
+    if rustversion::cfg!(since(1.68.0)) {
+        t.compile_fail("compile_tests/no_display_no_impl.rs");
+    }
+}

compile_tests/empty.rs

@@ -0,0 +1,4 @@
+#[derive(Debug, onlyerror::Error)]
+enum Error {}
+
+fn main() {}

compile_tests/multiple_non_signed.rs

@@ -0,0 +1,8 @@
+#[derive(Debug, onlyerror::Error)]
+enum Error {
+    First,
+    Second(usize),
+    Third { key: String, value: Vec<usize> },
+}
+
+fn main() {}

compile_tests/multiple_non_signed.stderr

@@ -0,0 +1,5 @@
+error: Required error message is missing
+ --> compile_tests/multiple_non_signed.rs:3:5
+  |
+3 |     First,
+  |     ^^^^^

compile_tests/multiple_one_non_signed.rs

@@ -0,0 +1,13 @@
+#[derive(Debug, onlyerror::Error)]
+enum Error {
+    /// First
+    First,
+    #[error("Second with {0}")]
+    Second(usize),
+    Third {
+        key: String,
+        value: Vec<usize>,
+    },
+}
+
+fn main() {}

compile_tests/multiple_one_non_signed.stderr

@@ -0,0 +1,5 @@
+error: Required error message is missing
+ --> compile_tests/multiple_one_non_signed.rs:7:5
+  |
+7 |     Third {
+  |     ^^^^^

compile_tests/multiple_variant.rs

@@ -0,0 +1,13 @@
+#![allow(dead_code)]
+
+#[derive(Debug, onlyerror::Error)]
+enum Error {
+    /// First
+    First,
+    #[error("Second with {0}")]
+    Second(usize),
+    #[error("Third with {key} and {value:?}")]
+    Third { key: String, value: Vec<usize> },
+}
+
+fn main() {}

compile_tests/no_display.rs

@@ -0,0 +1,17 @@
+#![allow(dead_code)]
+
+#[derive(Debug, onlyerror::Error)]
+#[no_display]
+enum Error {
+    First,
+    Second(usize),
+    Third { key: String, value: Vec<usize> },
+}
+
+impl core::fmt::Display for Error {
+    fn fmt(&self, f: &mut core::fmt::Formatter) -> core::result::Result<(), core::fmt::Error> {
+        write!(f, "Should work")
+    }
+}
+
+fn main() {}

compile_tests/no_display_no_impl.rs

@@ -0,0 +1,14 @@
+#![allow(dead_code)]
+
+#[derive(Debug, onlyerror::Error)]
+#[no_display]
+enum Error {
+    /// First
+    First,
+    #[error("Second with {0}")]
+    Second(usize),
+    #[error("Third with {key} and {value:?}")]
+    Third { key: String, value: Vec<usize> },
+}
+
+fn main() {}

compile_tests/no_display_no_impl.stderr

@@ -0,0 +1,11 @@
+error[E0277]: `Error` doesn't implement `std::fmt::Display`
+ --> compile_tests/no_display_no_impl.rs:3:17
+  |
+3 | #[derive(Debug, onlyerror::Error)]
+  |                 ^^^^^^^^^^^^^^^^ `Error` cannot be formatted with the default formatter
+  |
+  = help: the trait `std::fmt::Display` is not implemented for `Error`
+  = note: in format strings you may be able to use `{:?}` (or {:#?} for pretty-print) instead
+note: required by a bound in `std::error::Error`
+ --> $RUST/core/src/error.rs
+  = note: this error originates in the derive macro `onlyerror::Error` (in Nightly builds, run with -Z macro-backtrace for more info)

compile_tests/one_comment.rs

@@ -0,0 +1,9 @@
+#![allow(dead_code)]
+
+#[derive(Debug, onlyerror::Error)]
+enum Error {
+    /// One
+    One,
+}
+
+fn main() {}

compile_tests/one_non_signed.rs

@@ -0,0 +1,6 @@
+#[derive(Debug, onlyerror::Error)]
+enum Error {
+    One,
+}
+
+fn main() {}

compile_tests/one_non_signed.stderr

@@ -0,0 +1,5 @@
+error: Required error message is missing
+ --> compile_tests/one_non_signed.rs:3:5
+  |
+3 |     One,
+  |     ^^^

compile_tests/one_param.rs

@@ -0,0 +1,9 @@
+#![allow(dead_code)]
+
+#[derive(Debug, onlyerror::Error)]
+enum Error {
+    #[error("One")]
+    One,
+}
+
+fn main() {}