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use core::fmt::{self, Debug, Display}; macro_rules! with_backtrace { ($($i:item)*) => ($(#[cfg(all(feature = "backtrace", feature = "std"))]$i)*) } macro_rules! without_backtrace { ($($i:item)*) => ($(#[cfg(not(all(feature = "backtrace", feature = "std")))]$i)*) } without_backtrace! { /// A `Backtrace`. /// /// This is an opaque wrapper around the backtrace provided by /// libbacktrace. A variety of optimizations have been performed to avoid /// unnecessary or ill-advised work: /// /// - If this crate is compiled in `no_std` compatible mode, `Backtrace` /// is an empty struct, and will be completely compiled away. /// - If this crate is run without the `RUST_BACKTRACE` environmental /// variable enabled, the backtrace will not be generated at runtime. /// - Even if a backtrace is generated, the most expensive part of /// generating a backtrace is symbol resolution. This backtrace does not /// perform symbol resolution until it is actually read (e.g. by /// printing it). If the Backtrace is never used for anything, symbols /// never get resolved. /// /// Even with these optimizations, including a backtrace in your failure /// may not be appropriate to your use case. You are not required to put a /// backtrace in a custom `Fail` type. /// /// > (We have detected that this crate was documented with no_std /// > compatibility turned on. The version of this crate that has been /// > documented here will never generate a backtrace.) pub struct Backtrace { _secret: (), } impl Backtrace { /// Constructs a new backtrace. This will only create a real backtrace /// if the crate is compiled in std mode and the `RUST_BACKTRACE` /// environmental variable is activated. /// /// > (We have detected that this crate was documented with no_std /// > compatibility turned on. The version of this crate that has been /// > documented here will never generate a backtrace.) pub fn new() -> Backtrace { Backtrace { _secret: () } } #[cfg(feature = "std")] pub(crate) fn none() -> Backtrace { Backtrace { _secret: () } } #[cfg(feature = "std")] pub(crate) fn is_none(&self) -> bool { true } /// Returns true if displaying this backtrace would be an empty string. /// /// > (We have detected that this crate was documented with no_std /// > compatibility turned on. The version of this crate that has been /// > documented here will never generate a backtrace and this method /// > will always return true.) pub fn is_empty(&self) -> bool { true } } impl Default for Backtrace { fn default() -> Backtrace { Backtrace::new() } } impl Debug for Backtrace { fn fmt(&self, _: &mut fmt::Formatter) -> fmt::Result { Ok(()) } } impl Display for Backtrace { fn fmt(&self, _: &mut fmt::Formatter) -> fmt::Result { Ok(()) } } } with_backtrace! { extern crate backtrace; mod internal; use self::internal::InternalBacktrace; /// A `Backtrace`. /// /// This is an opaque wrapper around the backtrace provided by /// libbacktrace. A variety of optimizations have been performed to avoid /// unnecessary or ill-advised work: /// /// - If this crate is compiled in `no_std` compatible mode, `Backtrace` /// is an empty struct, and will be completely compiled away. /// - If this crate is run without the `RUST_BACKTRACE` environmental /// variable enabled, the backtrace will not be generated at runtime. /// - Even if a backtrace is generated, the most expensive part of /// generating a backtrace is symbol resolution. This backtrace does not /// perform symbol resolution until it is actually read (e.g. by /// printing it). If the Backtrace is never used for anything, symbols /// never get resolved. /// /// Even with these optimizations, including a backtrace in your failure /// may not be appropriate to your use case. You are not required to put a /// backtrace in a custom `Fail` type. pub struct Backtrace { internal: InternalBacktrace } impl Backtrace { /// Constructs a new backtrace. This will only create a real backtrace /// if the crate is compiled in std mode and the `RUST_BACKTRACE` /// environmental variable is activated. pub fn new() -> Backtrace { Backtrace { internal: InternalBacktrace::new() } } pub(crate) fn none() -> Backtrace { Backtrace { internal: InternalBacktrace::none() } } pub(crate) fn is_none(&self) -> bool { self.internal.is_none() } /// Returns true if displaying this backtrace would be an empty string. pub fn is_empty(&self) -> bool { self.internal.is_none() } } impl Default for Backtrace { fn default() -> Backtrace { Backtrace::new() } } impl Debug for Backtrace { fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { if let Some(bt) = self.internal.as_backtrace() { Debug::fmt(bt, f) } else { Ok(()) } } } impl Display for Backtrace { fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { if let Some(bt) = self.internal.as_backtrace() { Debug::fmt(bt, f) } else { Ok(()) } } } }