// Copyright 2014 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.

//! The data that we will serialize and deserialize.

use rustc::dep_graph::{DepNode, WorkProduct, WorkProductId};
use rustc::hir::def_id::DefIndex;
use std::sync::Arc;

use super::directory::DefPathIndex;

/// Data for use when recompiling the **current crate**.
#[derive(Debug, RustcEncodable, RustcDecodable)]
pub struct SerializedDepGraph {
    pub edges: Vec<SerializedEdge>,

    /// These are hashes of two things:
    /// - the HIR nodes in this crate
    /// - the metadata nodes from dependent crates we use
    ///
    /// In each case, we store a hash summarizing the contents of
    /// those items as they were at the time we did this compilation.
    /// In the case of HIR nodes, this hash is derived by walking the
    /// HIR itself. In the case of metadata nodes, the hash is loaded
    /// from saved state.
    ///
    /// When we do the next compile, we will load these back up and
    /// compare them against the hashes we see at that time, which
    /// will tell us what has changed, either in this crate or in some
    /// crate that we depend on.
    ///
    /// Because they will be reloaded, we don't store the DefId (which
    /// will be different when we next compile) related to each node,
    /// but rather the `DefPathIndex`. This can then be retraced
    /// to find the current def-id.
    pub hashes: Vec<SerializedHash>,
}

/// Represents a "reduced" dependency edge. Unlike the full dep-graph,
/// the dep-graph we serialize contains only edges `S -> T` where the
/// source `S` is something hashable (a HIR node or foreign metadata)
/// and the target `T` is something significant, like a work-product.
/// Normally, significant nodes are only those that have saved data on
/// disk, but in unit-testing the set of significant nodes can be
/// increased.
pub type SerializedEdge = (DepNode<DefPathIndex>, DepNode<DefPathIndex>);

#[derive(Debug, RustcEncodable, RustcDecodable)]
pub struct SerializedHash {
    /// def-id of thing being hashed
    pub dep_node: DepNode<DefPathIndex>,

    /// the hash as of previous compilation, computed by code in
    /// `hash` module
    pub hash: u64,
}

#[derive(Debug, RustcEncodable, RustcDecodable)]
pub struct SerializedWorkProduct {
    /// node that produced the work-product
    pub id: Arc<WorkProductId>,

    /// work-product data itself
    pub work_product: WorkProduct,
}

/// Data for use when downstream crates get recompiled.
#[derive(Debug, RustcEncodable, RustcDecodable)]
pub struct SerializedMetadataHashes {
    /// For each def-id defined in this crate that appears in the
    /// metadata, we hash all the inputs that were used when producing
    /// the metadata. We save this after compilation is done. Then,
    /// when some downstream crate is being recompiled, it can compare
    /// the hashes we saved against the hashes that it saw from
    /// before; this will tell it which of the items in this crate
    /// changed, which in turn implies what items in the downstream
    /// crate need to be recompiled.
    ///
    /// Note that we store the def-ids here. This is because we don't
    /// reload this file when we recompile this crate, we will just
    /// regenerate it completely with the current hashes and new def-ids.
    ///
    /// Then downstream creates will load up their
    /// `SerializedDepGraph`, which may contain `MetaData(X)` nodes
    /// where `X` refers to some item in this crate. That `X` will be
    /// a `DefPathIndex` that gets retracted to the current `DefId`
    /// (matching the one found in this structure).
    pub hashes: Vec<SerializedMetadataHash>,
}

/// The hash for some metadata that (when saving) will be exported
/// from this crate, or which (when importing) was exported by an
/// upstream crate.
#[derive(Debug, RustcEncodable, RustcDecodable)]
pub struct SerializedMetadataHash {
    pub def_index: DefIndex,

    /// the hash itself, computed by `calculate_item_hash`
    pub hash: u64,
}