1 //! Builder types for generating the "item data" section of the
2 //! metadata. This section winds up looking like this:
5 //! <common::data> // big list of item-like things...
6 //! <common::data_item> // ...for most def-ids, there is an entry.
7 //! </common::data_item>
11 //! As we generate this listing, we collect the offset of each
12 //! `data_item` entry and store it in an index. Then, when we load the
13 //! metadata, we can skip right to the metadata for a particular item.
15 //! In addition to the offset, we need to track the data that was used
16 //! to generate the contents of each `data_item`. This is so that we
17 //! can figure out which HIR nodes contributed to that data for
18 //! incremental compilation purposes.
20 //! The `IndexBuilder` facilitates both of these. It is created
21 //! with an `EncodingContext` (`ecx`), which it encapsulates.
22 //! It has one main method, `record()`. You invoke `record`
23 //! like so to create a new `data_item` element in the list:
26 //! index.record(some_def_id, callback_fn, data)
29 //! What record will do is to (a) record the current offset, (b) emit
30 //! the `common::data_item` tag, and then call `callback_fn` with the
31 //! given data as well as the `EncodingContext`. Once `callback_fn`
32 //! returns, the `common::data_item` tag will be closed.
34 //! `EncodingContext` does not offer the `record` method, so that we
35 //! can ensure that `common::data_item` elements are never nested.
37 //! In addition, while the `callback_fn` is executing, we will push a
38 //! task `MetaData(some_def_id)`, which can then observe the
39 //! reads/writes that occur in the task. For this reason, the `data`
40 //! argument that is given to the `callback_fn` must implement the
41 //! trait `DepGraphRead`, which indicates how to register reads on the
42 //! data in this new task (note that many types of data, such as
43 //! `DefId`, do not currently require any reads to be registered,
44 //! since they are not derived from a HIR node). This is also why we
45 //! give a callback fn, rather than taking a closure: it allows us to
46 //! easily control precisely what data is given to that fn.
48 use crate::encoder::EncodeContext;
49 use crate::index::Index;
51 use crate::isolated_encoder::IsolatedEncoder;
54 use rustc::hir::def_id::DefId;
55 use rustc::ty::TyCtxt;
58 use std::ops::{Deref, DerefMut};
60 /// Builder that can encode new items, adding them into the index.
61 /// Item encoding cannot be nested.
62 pub struct IndexBuilder<'a, 'b: 'a, 'tcx: 'b> {
64 pub ecx: &'a mut EncodeContext<'b, 'tcx>,
67 impl<'a, 'b, 'tcx> Deref for IndexBuilder<'a, 'b, 'tcx> {
68 type Target = EncodeContext<'b, 'tcx>;
69 fn deref(&self) -> &Self::Target {
74 impl<'a, 'b, 'tcx> DerefMut for IndexBuilder<'a, 'b, 'tcx> {
75 fn deref_mut(&mut self) -> &mut Self::Target {
80 impl<'a, 'b, 'tcx> IndexBuilder<'a, 'b, 'tcx> {
81 pub fn new(ecx: &'a mut EncodeContext<'b, 'tcx>) -> Self {
83 items: Index::new(ecx.tcx.hir().definitions().def_index_counts_lo_hi()),
88 /// Emit the data for a def-id to the metadata. The function to
89 /// emit the data is `op`, and it will be given `data` as
90 /// arguments. This `record` function will call `op` to generate
91 /// the `Entry` (which may point to other encoded information)
92 /// and will then record the `Lazy<Entry>` for use in the index.
94 /// In addition, it will setup a dep-graph task to track what data
95 /// `op` accesses to generate the metadata, which is later used by
96 /// incremental compilation to compute a hash for the metadata and
99 /// The reason that `op` is a function pointer, and not a closure,
100 /// is that we want to be able to completely track all data it has
101 /// access to, so that we can be sure that `DATA: DepGraphRead`
102 /// holds, and that it is therefore not gaining "secret" access to
103 /// bits of HIR or other state that would not be trackd by the
105 pub fn record<'x, DATA>(&'x mut self,
107 op: fn(&mut IsolatedEncoder<'x, 'b, 'tcx>, DATA) -> Entry<'tcx>,
109 where DATA: DepGraphRead
111 assert!(id.is_local());
113 // We don't track this since we are explicitly computing the incr. comp.
114 // hashes anyway. In theory we could do some tracking here and use it to
115 // avoid rehashing things (and instead cache the hashes) but it's
116 // unclear whether that would be a win since hashing is cheap enough.
117 self.ecx.tcx.dep_graph.with_ignore(move || {
118 let mut entry_builder = IsolatedEncoder::new(self.ecx);
119 let entry = op(&mut entry_builder, data);
120 let entry = entry_builder.lazy(&entry);
122 self.items.record(id, entry);
126 pub fn into_items(self) -> Index {
131 /// Trait used for data that can be passed from outside a dep-graph
132 /// task. The data must either be of some safe type, such as a
133 /// `DefId` index, or implement the `read` method so that it can add
134 /// a read of whatever dep-graph nodes are appropriate.
135 pub trait DepGraphRead {
136 fn read(&self, tcx: TyCtxt<'_, '_, '_>);
139 impl DepGraphRead for DefId {
140 fn read(&self, _tcx: TyCtxt<'_, '_, '_>) {}
143 impl DepGraphRead for ast::NodeId {
144 fn read(&self, _tcx: TyCtxt<'_, '_, '_>) {}
147 impl<T> DepGraphRead for Option<T>
148 where T: DepGraphRead
150 fn read(&self, tcx: TyCtxt<'_, '_, '_>) {
152 Some(ref v) => v.read(tcx),
158 impl<T> DepGraphRead for [T]
159 where T: DepGraphRead
161 fn read(&self, tcx: TyCtxt<'_, '_, '_>) {
168 macro_rules! read_tuple {
169 ($($name:ident),*) => {
170 impl<$($name),*> DepGraphRead for ($($name),*)
171 where $($name: DepGraphRead),*
173 #[allow(non_snake_case)]
174 fn read(&self, tcx: TyCtxt<'_, '_, '_>) {
175 let &($(ref $name),*) = self;
182 read_tuple!(A, B, C);
184 macro_rules! read_hir {
186 impl<'tcx> DepGraphRead for &'tcx $t {
187 fn read(&self, tcx: TyCtxt<'_, '_, '_>) {
188 tcx.hir().read(self.id);
193 read_hir!(hir::Item);
194 read_hir!(hir::ImplItem);
195 read_hir!(hir::TraitItem);
196 read_hir!(hir::ForeignItem);
197 read_hir!(hir::MacroDef);
199 /// Leaks access to a value of type T without any tracking. This is
200 /// suitable for ambiguous types like `usize`, which *could* represent
201 /// tracked data (e.g., if you read it out of a HIR node) or might not
202 /// (e.g., if it's an index). Adding in an `Untracked` is an
203 /// assertion, essentially, that the data does not need to be tracked
204 /// (or that read edges will be added by some other way).
206 /// A good idea is to add to each use of `Untracked` an explanation of
207 /// why this value is ok.
208 pub struct Untracked<T>(pub T);
210 impl<T> DepGraphRead for Untracked<T> {
211 fn read(&self, _tcx: TyCtxt<'_, '_, '_>) {}
214 /// Newtype that can be used to package up misc data extracted from a
215 /// HIR node that doesn't carry its own id. This will allow an
216 /// arbitrary `T` to be passed in, but register a read on the given
218 pub struct FromId<T>(pub ast::NodeId, pub T);
220 impl<T> DepGraphRead for FromId<T> {
221 fn read(&self, tcx: TyCtxt<'_, '_, '_>) {
222 tcx.hir().read(self.0);