547d9374d2
Encode spans relative to the enclosing item The aim of this PR is to avoid recomputing queries when code is moved without modification. MCP at https://github.com/rust-lang/compiler-team/issues/443 This is achieved by : 1. storing the HIR owner LocalDefId information inside the span; 2. encoding and decoding spans relative to the enclosing item in the incremental on-disk cache; 3. marking a dependency to the `source_span(LocalDefId)` query when we translate a span from the short (`Span`) representation to its explicit (`SpanData`) representation. Since all client code uses `Span`, step 3 ensures that all manipulations of span byte positions actually create the dependency edge between the caller and the `source_span(LocalDefId)`. This query return the actual absolute span of the parent item. As a consequence, any source code motion that changes the absolute byte position of a node will either: - modify the distance to the parent's beginning, so change the relative span's hash; - dirty `source_span`, and trigger the incremental recomputation of all code that depends on the span's absolute byte position. With this scheme, I believe the dependency tracking to be accurate. For the moment, the spans are marked during lowering. I'd rather do this during def-collection, but the AST MutVisitor is not practical enough just yet. The only difference is that we attach macro-expanded spans to their expansion point instead of the macro itself. |
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