Auto merge of #84373 - cjgillot:resolve-span, r=michaelwoerister,petr…

…ochenkov

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 rust-lang/compiler-team#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.

src/macros.rs

@@ -1247,7 +1247,12 @@ impl MacroParser {
                 let data = delimited_span.entire().data();
                 (
                     data.hi,
-                    Span::new(data.lo + BytePos(1), data.hi - BytePos(1), data.ctxt),
+                    Span::new(
+                        data.lo + BytePos(1),
+                        data.hi - BytePos(1),
+                        data.ctxt,
+                        data.parent,
+                    ),
                     delimited_span.entire(),
                 )
             }

src/utils.rs

@@ -356,11 +356,11 @@ macro_rules! source {
 }
 
 pub(crate) fn mk_sp(lo: BytePos, hi: BytePos) -> Span {
-    Span::new(lo, hi, SyntaxContext::root())
+    Span::new(lo, hi, SyntaxContext::root(), None)
 }
 
 pub(crate) fn mk_sp_lo_plus_one(lo: BytePos) -> Span {
-    Span::new(lo, lo + BytePos(1), SyntaxContext::root())
+    Span::new(lo, lo + BytePos(1), SyntaxContext::root(), None)
 }
 
 // Returns `true` if the given span does not intersect with file lines.