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    //! Library for applying diagnostic suggestions to source code.
    //!
    //! This is a low-level library. You pass it the [JSON output] from `rustc`,
    //! and you can then use it to apply suggestions to in-memory strings.
    //! This library doesn't execute commands, or read or write from the filesystem.
    //!
    //! If you are looking for the [`cargo fix`] implementation, the core of it is
    //! located in [`cargo::ops::fix`].
    //!
    //! [`cargo fix`]: https://doc.rust-lang.org/cargo/commands/cargo-fix.html
    //! [`cargo::ops::fix`]: https://github.com/rust-lang/cargo/blob/master/src/cargo/ops/fix.rs
    //! [JSON output]: diagnostics
    //!
    //! The general outline of how to use this library is:
    //!
    //! 1. Call `rustc` and collect the JSON data.
    //! 2. Pass the json data to [`get_suggestions_from_json`].
    //! 3. Create a [`CodeFix`] with the source of a file to modify.
    //! 4. Call [`CodeFix::apply`] to apply a change.
    //! 5. Call [`CodeFix::finish`] to get the result and write it back to disk.

    use std::collections::HashSet;
    use std::ops::Range;

    pub mod diagnostics;
    mod error;
    mod replace;

    use diagnostics::Diagnostic;
    use diagnostics::DiagnosticSpan;
    pub use error::Error;

    /// A filter to control which suggestion should be applied.
    #[derive(Debug, Clone, Copy)]
    pub enum Filter {
        /// For [`diagnostics::Applicability::MachineApplicable`] only.
        MachineApplicableOnly,
        /// Everything is included. YOLO!
        Everything,
    }

    /// Collects code [`Suggestion`]s from one or more compiler diagnostic lines.
    ///
    /// Fails if any of diagnostic line `input` is not a valid [`Diagnostic`] JSON.
    ///
    /// * `only` --- only diagnostics with code in a set of error codes would be collected.
    pub fn get_suggestions_from_json<S: ::std::hash::BuildHasher>(
        input: &str,
        only: &HashSet<String, S>,
        filter: Filter,
    ) -> serde_json::error::Result<Vec<Suggestion>> {
        let mut result = Vec::new();
        for cargo_msg in serde_json::Deserializer::from_str(input).into_iter::<Diagnostic>() {
            // One diagnostic line might have multiple suggestions
            result.extend(collect_suggestions(&cargo_msg?, only, filter));
        }
        Ok(result)
    }

    #[derive(Debug, Copy, Clone, Hash, PartialEq, Eq)]
    pub struct LinePosition {
        pub line: usize,
        pub column: usize,
    }

    impl std::fmt::Display for LinePosition {
        fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
            write!(f, "{}:{}", self.line, self.column)
        }
    }

    #[derive(Debug, Copy, Clone, Hash, PartialEq, Eq)]
    pub struct LineRange {
        pub start: LinePosition,
        pub end: LinePosition,
    }

    impl std::fmt::Display for LineRange {
        fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
            write!(f, "{}-{}", self.start, self.end)
        }
    }

    /// An error/warning and possible solutions for fixing it
    #[derive(Debug, Clone, Hash, PartialEq, Eq)]
    pub struct Suggestion {
        pub message: String,
        pub snippets: Vec<Snippet>,
        pub solutions: Vec<Solution>,
    }

    /// Solution to a diagnostic item.
    #[derive(Debug, Clone, Hash, PartialEq, Eq)]
    pub struct Solution {
        /// The error message of the diagnostic item.
        pub message: String,
        /// Possible solutions to fix the error.
        pub replacements: Vec<Replacement>,
    }

    /// Represents code that will get replaced.
    #[derive(Debug, Clone, Hash, PartialEq, Eq)]
    pub struct Snippet {
        pub file_name: String,
        pub line_range: LineRange,
        pub range: Range<usize>,
    }

    /// Represents a replacement of a `snippet`.
    #[derive(Debug, Clone, Hash, PartialEq, Eq)]
    pub struct Replacement {
        /// Code snippet that gets replaced.
        pub snippet: Snippet,
        /// The replacement of the snippet.
        pub replacement: String,
    }

    /// Converts a [`DiagnosticSpan`] to a [`Snippet`].
    fn span_to_snippet(span: &DiagnosticSpan) -> Snippet {
        Snippet {
            file_name: span.file_name.clone(),
            line_range: LineRange {
                start: LinePosition {
                    line: span.line_start,
                    column: span.column_start,
                },
                end: LinePosition {
                    line: span.line_end,
                    column: span.column_end,
                },
            },
            range: (span.byte_start as usize)..(span.byte_end as usize),
        }
    }

    /// Converts a [`DiagnosticSpan`] into a [`Replacement`].
    fn collect_span(span: &DiagnosticSpan) -> Option<Replacement> {
        let snippet = span_to_snippet(span);
        let replacement = span.suggested_replacement.clone()?;
        Some(Replacement {
            snippet,
            replacement,
        })
    }

    /// Collects code [`Suggestion`]s from a single compiler diagnostic line.
    ///
    /// * `only` --- only diagnostics with code in a set of error codes would be collected.
    pub fn collect_suggestions<S: ::std::hash::BuildHasher>(
        diagnostic: &Diagnostic,
        only: &HashSet<String, S>,
        filter: Filter,
    ) -> Option<Suggestion> {
        if !only.is_empty() {
            if let Some(ref code) = diagnostic.code {
                if !only.contains(&code.code) {
                    // This is not the code we are looking for
                    return None;
                }
            } else {
                // No code, probably a weird builtin warning/error
                return None;
            }
        }

        let snippets = diagnostic.spans.iter().map(span_to_snippet).collect();

        let solutions: Vec<_> = diagnostic
            .children
            .iter()
            .filter_map(|child| {
                let replacements: Vec<_> = child
                    .spans
                    .iter()
                    .filter(|span| {
                        use crate::diagnostics::Applicability::*;
                        use crate::Filter::*;

                        match (filter, &span.suggestion_applicability) {
                            (MachineApplicableOnly, Some(MachineApplicable)) => true,
                            (MachineApplicableOnly, _) => false,
                            (Everything, _) => true,
                        }
                    })
                    .filter_map(collect_span)
                    .collect();
                if !replacements.is_empty() {
                    Some(Solution {
                        message: child.message.clone(),
                        replacements,
                    })
                } else {
                    None
                }
            })
            .collect();

        if solutions.is_empty() {
            None
        } else {
            Some(Suggestion {
                message: diagnostic.message.clone(),
                snippets,
                solutions,
            })
        }
    }

    /// Represents a code fix. This doesn't write to disks but is only in memory.
    ///
    /// The general way to use this is:
    ///
    /// 1. Feeds the source of a file to [`CodeFix::new`].
    /// 2. Calls [`CodeFix::apply`] to apply suggestions to the source code.
    /// 3. Calls [`CodeFix::finish`] to get the "fixed" code.
    pub struct CodeFix {
        data: replace::Data,
        /// Whether or not the data has been modified.
        modified: bool,
    }

    impl CodeFix {
        /// Creates a `CodeFix` with the source of a file to modify.
        pub fn new(s: &str) -> CodeFix {
            CodeFix {
                data: replace::Data::new(s.as_bytes()),
                modified: false,
            }
        }

        /// Applies a suggestion to the code.
        pub fn apply(&mut self, suggestion: &Suggestion) -> Result<(), Error> {
            for sol in &suggestion.solutions {
                for r in &sol.replacements {
                    self.data
                        .replace_range(r.snippet.range.clone(), r.replacement.as_bytes())?;
                    self.modified = true;
                }
            }
            Ok(())
        }

        /// Gets the result of the "fixed" code.
        pub fn finish(&self) -> Result<String, Error> {
            Ok(String::from_utf8(self.data.to_vec())?)
        }

        /// Returns whether or not the data has been modified.
        pub fn modified(&self) -> bool {
            self.modified
        }
    }

    /// Applies multiple `suggestions` to the given `code`.
    pub fn apply_suggestions(code: &str, suggestions: &[Suggestion]) -> Result<String, Error> {
        let mut fix = CodeFix::new(code);
        for suggestion in suggestions.iter().rev() {
            fix.apply(suggestion)?;
        }
        fix.finish()
    }