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

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.

compiler/rustc_expand/src/base.rs

@@ -15,7 +15,7 @@ use rustc_lint_defs::builtin::PROC_MACRO_BACK_COMPAT;
 use rustc_lint_defs::BuiltinLintDiagnostics;
 use rustc_parse::{self, nt_to_tokenstream, parser, MACRO_ARGUMENTS};
 use rustc_session::{parse::ParseSess, Limit, Session};
-use rustc_span::def_id::{CrateNum, DefId};
+use rustc_span::def_id::{CrateNum, DefId, LocalDefId};
 use rustc_span::edition::Edition;
 use rustc_span::hygiene::{AstPass, ExpnData, ExpnKind, LocalExpnId};
 use rustc_span::source_map::SourceMap;
@@ -843,6 +843,7 @@ pub type DeriveResolutions = Vec<(ast::Path, Annotatable, Option<Lrc<SyntaxExten
 
 pub trait ResolverExpand {
     fn next_node_id(&mut self) -> NodeId;
+    fn invocation_parent(&self, id: LocalExpnId) -> LocalDefId;
 
     fn resolve_dollar_crates(&mut self);
     fn visit_ast_fragment_with_placeholders(

compiler/rustc_expand/src/expand.rs

@@ -588,7 +588,7 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
         // Resolve `$crate`s in the fragment for pretty-printing.
         self.cx.resolver.resolve_dollar_crates();
 
-        let invocations = {
+        let mut invocations = {
             let mut collector = InvocationCollector {
                 // Non-derive macro invocations cannot see the results of cfg expansion - they
                 // will either be removed along with the item, or invoked before the cfg/cfg_attr
@@ -613,6 +613,19 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
             self.cx
                 .resolver
                 .visit_ast_fragment_with_placeholders(self.cx.current_expansion.id, &fragment);
+
+            if self.cx.sess.opts.debugging_opts.incremental_relative_spans {
+                for (invoc, _) in invocations.iter_mut() {
+                    let expn_id = invoc.expansion_data.id;
+                    let parent_def = self.cx.resolver.invocation_parent(expn_id);
+                    let span = match &mut invoc.kind {
+                        InvocationKind::Bang { ref mut span, .. } => span,
+                        InvocationKind::Attr { attr, .. } => &mut attr.span,
+                        InvocationKind::Derive { path, .. } => &mut path.span,
+                    };
+                    *span = span.with_parent(Some(parent_def));
+                }
+            }
         }
 
         (fragment, invocations)

compiler/rustc_expand/src/proc_macro_server.rs

@@ -745,7 +745,7 @@ impl server::Span for Rustc<'_> {
         self.sess.source_map().lookup_char_pos(span.lo()).file
     }
     fn parent(&mut self, span: Self::Span) -> Option<Self::Span> {
-        span.parent()
+        span.parent_callsite()
     }
     fn source(&mut self, span: Self::Span) -> Self::Span {
         span.source_callsite()