//! Some facilities for tracking how codegen-units are reused during incremental
//! compilation. This is used for incremental compilation tests and debug
//! output.

use rustc_data_structures::fx::FxHashMap;
use rustc_span::{Span, Symbol};
use std::sync::{Arc, Mutex};
use tracing::debug;

#[derive(Copy, Clone, Debug, PartialEq, PartialOrd)]
pub enum CguReuse {
    No,
    PreLto,
    PostLto,
}

#[derive(Copy, Clone, Debug, PartialEq)]
pub enum ComparisonKind {
    Exact,
    AtLeast,
}

struct TrackerData {
    actual_reuse: FxHashMap<String, CguReuse>,
    expected_reuse: FxHashMap<String, (String, SendSpan, CguReuse, ComparisonKind)>,
}

// Span does not implement `Send`, so we can't just store it in the shared
// `TrackerData` object. Instead of splitting up `TrackerData` into shared and
// non-shared parts (which would be complicated), we just mark the `Span` here
// explicitly as `Send`. That's safe because the span data here is only ever
// accessed from the main thread.
struct SendSpan(Span);
unsafe impl Send for SendSpan {}

#[derive(Clone)]
pub struct CguReuseTracker {
    data: Option<Arc<Mutex<TrackerData>>>,
}

impl CguReuseTracker {
    pub fn new() -> CguReuseTracker {
        let data =
            TrackerData { actual_reuse: Default::default(), expected_reuse: Default::default() };

        CguReuseTracker { data: Some(Arc::new(Mutex::new(data))) }
    }

    pub fn new_disabled() -> CguReuseTracker {
        CguReuseTracker { data: None }
    }

    pub fn set_actual_reuse(&self, cgu_name: &str, kind: CguReuse) {
        if let Some(ref data) = self.data {
            debug!("set_actual_reuse({cgu_name:?}, {kind:?})");

            let prev_reuse = data.lock().unwrap().actual_reuse.insert(cgu_name.to_string(), kind);

            if let Some(prev_reuse) = prev_reuse {
                // The only time it is legal to overwrite reuse state is when
                // we discover during ThinLTO that we can actually reuse the
                // post-LTO version of a CGU.
                assert_eq!(prev_reuse, CguReuse::PreLto);
            }
        }
    }

    pub fn set_expectation(
        &self,
        cgu_name: Symbol,
        cgu_user_name: &str,
        error_span: Span,
        expected_reuse: CguReuse,
        comparison_kind: ComparisonKind,
    ) {
        if let Some(ref data) = self.data {
            debug!("set_expectation({cgu_name:?}, {expected_reuse:?}, {comparison_kind:?})");
            let mut data = data.lock().unwrap();

            data.expected_reuse.insert(
                cgu_name.to_string(),
                (cgu_user_name.to_string(), SendSpan(error_span), expected_reuse, comparison_kind),
            );
        }
    }

    pub fn check_expected_reuse(&self, diag: &rustc_errors::Handler) {
        if let Some(ref data) = self.data {
            let data = data.lock().unwrap();

            for (cgu_name, &(ref cgu_user_name, ref error_span, expected_reuse, comparison_kind)) in
                &data.expected_reuse
            {
                if let Some(&actual_reuse) = data.actual_reuse.get(cgu_name) {
                    let (error, at_least) = match comparison_kind {
                        ComparisonKind::Exact => (expected_reuse != actual_reuse, false),
                        ComparisonKind::AtLeast => (actual_reuse < expected_reuse, true),
                    };

                    if error {
                        let at_least = if at_least { "at least " } else { "" };
                        let msg = format!(
                            "CGU-reuse for `{cgu_user_name}` is `{actual_reuse:?}` but \
                                           should be {at_least}`{expected_reuse:?}`"
                        );
                        diag.span_err(error_span.0, &msg);
                    }
                } else {
                    let msg = format!(
                        "CGU-reuse for `{cgu_user_name}` (mangled: `{cgu_name}`) was \
                                       not recorded"
                    );
                    diag.span_fatal(error_span.0, &msg)
                }
            }
        }
    }
}