From 698f8c2f01ea549d77d7dc3338a12e04c11057b9 Mon Sep 17 00:00:00 2001
From: Daniel Baumann <daniel.baumann@progress-linux.org>
Date: Wed, 17 Apr 2024 14:02:58 +0200
Subject: Adding upstream version 1.64.0+dfsg1.

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
---
 .../rustc_error_codes/src/error_codes/E0277.md     | 87 ++++++++++++++++++++++
 1 file changed, 87 insertions(+)
 create mode 100644 compiler/rustc_error_codes/src/error_codes/E0277.md

(limited to 'compiler/rustc_error_codes/src/error_codes/E0277.md')

diff --git a/compiler/rustc_error_codes/src/error_codes/E0277.md b/compiler/rustc_error_codes/src/error_codes/E0277.md
new file mode 100644
index 000000000..5f05b59d5
--- /dev/null
+++ b/compiler/rustc_error_codes/src/error_codes/E0277.md
@@ -0,0 +1,87 @@
+You tried to use a type which doesn't implement some trait in a place which
+expected that trait.
+
+Erroneous code example:
+
+```compile_fail,E0277
+// here we declare the Foo trait with a bar method
+trait Foo {
+    fn bar(&self);
+}
+
+// we now declare a function which takes an object implementing the Foo trait
+fn some_func<T: Foo>(foo: T) {
+    foo.bar();
+}
+
+fn main() {
+    // we now call the method with the i32 type, which doesn't implement
+    // the Foo trait
+    some_func(5i32); // error: the trait bound `i32 : Foo` is not satisfied
+}
+```
+
+In order to fix this error, verify that the type you're using does implement
+the trait. Example:
+
+```
+trait Foo {
+    fn bar(&self);
+}
+
+// we implement the trait on the i32 type
+impl Foo for i32 {
+    fn bar(&self) {}
+}
+
+fn some_func<T: Foo>(foo: T) {
+    foo.bar(); // we can now use this method since i32 implements the
+               // Foo trait
+}
+
+fn main() {
+    some_func(5i32); // ok!
+}
+```
+
+Or in a generic context, an erroneous code example would look like:
+
+```compile_fail,E0277
+fn some_func<T>(foo: T) {
+    println!("{:?}", foo); // error: the trait `core::fmt::Debug` is not
+                           //        implemented for the type `T`
+}
+
+fn main() {
+    // We now call the method with the i32 type,
+    // which *does* implement the Debug trait.
+    some_func(5i32);
+}
+```
+
+Note that the error here is in the definition of the generic function. Although
+we only call it with a parameter that does implement `Debug`, the compiler
+still rejects the function. It must work with all possible input types. In
+order to make this example compile, we need to restrict the generic type we're
+accepting:
+
+```
+use std::fmt;
+
+// Restrict the input type to types that implement Debug.
+fn some_func<T: fmt::Debug>(foo: T) {
+    println!("{:?}", foo);
+}
+
+fn main() {
+    // Calling the method is still fine, as i32 implements Debug.
+    some_func(5i32);
+
+    // This would fail to compile now:
+    // struct WithoutDebug;
+    // some_func(WithoutDebug);
+}
+```
+
+Rust only looks at the signature of the called function, as such it must
+already specify all requirements that will be used for every type parameter.
-- 
cgit v1.2.3