Don't panic when stdout doesn't exist

0000-stdout-existential-crisis.md

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+- Feature Name: stdout_existential_crisis
+- Start Date: 2015-03-25
+- RFC PR: (leave this empty)
+- Rust Issue: (leave this empty)
+
+# Summary
+
+When calling `println!` it currently causes a panic if `stdout` does not exist. Change this to ignore this specific error and simply void the output.
+
+# Motivation
+
+On Linux `stdout` almost always exists, so when people write games and turn off the terminal there is still an `stdout` that they write to. Then when getting the code to run on Windows, when the console is disabled, suddenly `stdout` doesn't exist and `println!` panicks. This behavior difference is frustrating to developers trying to move to Windows.
+
+There is also precedent with C and C++. On both Linux and Windows, if `stdout` is closed or doesn't exist, neither platform will error when attempting to print to the console.
+
+# Detailed design
+
+When using any of the convenience macros that write to either `stdout` or `stderr`, such as `println!` `print!` `panic!` and `assert!`, change the implementation to ignore the specific error of `stdout` or `stderr` not existing. The behavior of all other errors will be unaffected. This can be implemented by redirecting `stdout` and `stderr` to `std::io::sink` if the original handles do not exist.
+
+Update the methods `std::io::stdin` `std::io::stdout` and `std::io::stderr` as follows:
+* If `stdout` or `stderr` does not exist, return the equivalent of `std::io::sink`.
+* If `stdin` does not exist, return the equivalent of `std::io::empty`.
+* For the raw versions, return a `Result`, and if the respective handle does not exist, return an `Err`.
+
+# Drawbacks
+
+* Hides an error from the user which we may want to expose and may lead to people missing panicks occuring in threads.
+* Some languages, such as Ruby and Python, do throw an exception when stdout is missing.
+
+# Alternatives
+
+* Make `println!` `print!` `panic!` `assert!` return errors that the user has to handle. This would lose a large part of the convenience of these macros.
+* Continue with the status quo and panic if `stdout` or `stderr` doesn't exist.
+* For `std::io::stdin` `std::io::stdout` and `std::io::stderr`, make them return a `Result`. This would be a breaking change to the signature, so if this is desired it should be done immediately before 1.0.
+** Alternatively, make the objects returned by these methods error upon attempting to write to/read from them if their respective handle doesn't exist.
+
+# Unresolved questions
+
+* Which is better? Breaking the signatures of those three methods in `std::io`, making them silently redirect to `empty`/`sink`, or erroring upon attempting to write to/read from the handle?