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    // Copyright 2017 The Rust Project Developers. See the COPYRIGHT
    // file at the top-level directory of this distribution and at
    // http://rust-lang.org/COPYRIGHT.
    //
    // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
    // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
    // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
    // option. This file may not be copied, modified, or distributed
    // except according to those terms.

    use Span;

    use rustc_errors as rustc;

    /// An enum representing a diagnostic level.
    #[unstable(feature = "proc_macro", issue = "38356")]
    #[derive(Copy, Clone, Debug)]
    pub enum Level {
        /// An error.
        Error,
        /// A warning.
        Warning,
        /// A note.
        Note,
        /// A help message.
        Help,
        #[doc(hidden)]
        __Nonexhaustive,
    }

    /// A structure representing a diagnostic message and associated children
    /// messages.
    #[unstable(feature = "proc_macro", issue = "38356")]
    #[derive(Clone, Debug)]
    pub struct Diagnostic {
        level: Level,
        message: String,
        span: Option<Span>,
        children: Vec<Diagnostic>
    }

    macro_rules! diagnostic_child_methods {
        ($spanned:ident, $regular:ident, $level:expr) => (
            /// Add a new child diagnostic message to `self` with the level
            /// identified by this methods name with the given `span` and `message`.
            #[unstable(feature = "proc_macro", issue = "38356")]
            pub fn $spanned<T: Into<String>>(mut self, span: Span, message: T) -> Diagnostic {
                self.children.push(Diagnostic::spanned(span, $level, message));
                self
            }

            /// Add a new child diagnostic message to `self` with the level
            /// identified by this method's name with the given `message`.
            #[unstable(feature = "proc_macro", issue = "38356")]
            pub fn $regular<T: Into<String>>(mut self, message: T) -> Diagnostic {
                self.children.push(Diagnostic::new($level, message));
                self
            }
        )
    }

    impl Diagnostic {
        /// Create a new diagnostic with the given `level` and `message`.
        #[unstable(feature = "proc_macro", issue = "38356")]
        pub fn new<T: Into<String>>(level: Level, message: T) -> Diagnostic {
            Diagnostic {
                level: level,
                message: message.into(),
                span: None,
                children: vec![]
            }
        }

        /// Create a new diagnostic with the given `level` and `message` pointing to
        /// the given `span`.
        #[unstable(feature = "proc_macro", issue = "38356")]
        pub fn spanned<T: Into<String>>(span: Span, level: Level, message: T) -> Diagnostic {
            Diagnostic {
                level: level,
                message: message.into(),
                span: Some(span),
                children: vec![]
            }
        }

        diagnostic_child_methods!(span_error, error, Level::Error);
        diagnostic_child_methods!(span_warning, warning, Level::Warning);
        diagnostic_child_methods!(span_note, note, Level::Note);
        diagnostic_child_methods!(span_help, help, Level::Help);

        /// Returns the diagnostic `level` for `self`.
        #[unstable(feature = "proc_macro", issue = "38356")]
        pub fn level(&self) -> Level {
            self.level
        }

        /// Emit the diagnostic.
        #[unstable(feature = "proc_macro", issue = "38356")]
        pub fn emit(self) {
            ::__internal::with_sess(move |sess, _| {
                let handler = &sess.span_diagnostic;
                let level = __internal::level_to_internal_level(self.level);
                let mut diag = rustc::DiagnosticBuilder::new(handler, level, &*self.message);

                if let Some(span) = self.span {
                    diag.set_span(span.0);
                }

                for child in self.children {
                    let span = child.span.map(|s| s.0);
                    let level = __internal::level_to_internal_level(child.level);
                    diag.sub(level, &*child.message, span);
                }

                diag.emit();
            });
        }
    }

    #[unstable(feature = "proc_macro_internals", issue = "27812")]
    #[doc(hidden)]
    pub mod __internal {
        use super::{Level, rustc};

        pub fn level_to_internal_level(level: Level) -> rustc::Level {
            match level {
                Level::Error => rustc::Level::Error,
                Level::Warning => rustc::Level::Warning,
                Level::Note => rustc::Level::Note,
                Level::Help => rustc::Level::Help,
                Level::__Nonexhaustive => unreachable!("Level::__Nonexhaustive")
            }
        }
    }

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