Auto merge of #46338 - michaelwoerister:lazy-diagnostics, r=nikomatsakis

incr.comp.: Load cached diagnostics lazily and allow more things in the cache.

This PR implements makes two changes:
1. Diagnostics are loaded lazily from the incr. comp. cache now. This turned out to be necessary for correctness because diagnostics contain `Span` values and deserializing those requires that the source file they point to is still around in the current compilation session. Obviously this isn't always the case. Loading them lazily allows for never touching diagnostics that are not valid anymore.
2. The compiler can now deal with there being no cache entry for a given query invocation. Before, all query results of a cacheable query were always expected to be present in the cache. Now, the compiler can fall back to re-computing the result if there is no cache entry found. This allows for caching things that we cannot force from dep-node (like the `symbol_name` query). In such a case we'll just have a "best effort" caching strategy.

~~This PR is based on #46301 (=first 2 commits), so please don't merge until that has landed. The rest of the commits are ready for review though.~~

r? @nikomatsakis

src/librustc/dep_graph/graph.rs

@@ -461,10 +461,10 @@ impl DepGraph {
         self.data.as_ref().and_then(|data| data.colors.borrow().get(dep_node).cloned())
     }
 
-    pub fn try_mark_green(&self,
-                          tcx: TyCtxt,
-                          dep_node: &DepNode)
-                          -> Option<DepNodeIndex> {
+    pub fn try_mark_green<'tcx>(&self,
+                                tcx: TyCtxt<'_, 'tcx, 'tcx>,
+                                dep_node: &DepNode)
+                                -> Option<DepNodeIndex> {
         debug!("try_mark_green({:?}) - BEGIN", dep_node);
         let data = self.data.as_ref().unwrap();
 
@@ -621,7 +621,7 @@ impl DepGraph {
         // ... emitting any stored diagnostic ...
         {
             let diagnostics = tcx.on_disk_query_result_cache
-                                 .load_diagnostics(prev_dep_node_index);
+                                 .load_diagnostics(tcx, prev_dep_node_index);
 
             if diagnostics.len() > 0 {
                 let handle = tcx.sess.diagnostic();

src/librustc/ich/hcx.rs

@@ -28,7 +28,7 @@ use syntax::attr;
 use syntax::codemap::CodeMap;
 use syntax::ext::hygiene::SyntaxContext;
 use syntax::symbol::Symbol;
-use syntax_pos::Span;
+use syntax_pos::{Span, DUMMY_SP};
 
 use rustc_data_structures::stable_hasher::{HashStable, StableHashingContextProvider,
                                            StableHasher, StableHasherResult,
@@ -362,64 +362,53 @@ impl<'gcx> HashStable<StableHashingContext<'gcx>> for Span {
     fn hash_stable<W: StableHasherResult>(&self,
                                           hcx: &mut StableHashingContext<'gcx>,
                                           hasher: &mut StableHasher<W>) {
-        use syntax_pos::Pos;
+        const TAG_VALID_SPAN: u8 = 0;
+        const TAG_INVALID_SPAN: u8 = 1;
+        const TAG_EXPANSION: u8 = 0;
+        const TAG_NO_EXPANSION: u8 = 1;
 
         if !hcx.hash_spans {
             return
         }
 
+        if *self == DUMMY_SP {
+            return std_hash::Hash::hash(&TAG_INVALID_SPAN, hasher);
+        }
+
         // If this is not an empty or invalid span, we want to hash the last
         // position that belongs to it, as opposed to hashing the first
         // position past it.
         let span = self.data();
-        let span_hi = if span.hi > span.lo {
-            // We might end up in the middle of a multibyte character here,
-            // but that's OK, since we are not trying to decode anything at
-            // this position.
-            span.hi - ::syntax_pos::BytePos(1)
-        } else {
-            span.hi
-        };
 
-        {
-            let loc1 = hcx.codemap().byte_pos_to_line_and_col(span.lo);
-            let loc1 = loc1.as_ref()
-                           .map(|&(ref fm, line, col)| (&fm.name[..], line, col.to_usize()))
-                           .unwrap_or(("???", 0, 0));
-
-            let loc2 = hcx.codemap().byte_pos_to_line_and_col(span_hi);
-            let loc2 = loc2.as_ref()
-                           .map(|&(ref fm, line, col)| (&fm.name[..], line, col.to_usize()))
-                           .unwrap_or(("???", 0, 0));
-
-            if loc1.0 == loc2.0 {
-                std_hash::Hash::hash(&0u8, hasher);
-
-                std_hash::Hash::hash(loc1.0, hasher);
-                std_hash::Hash::hash(&loc1.1, hasher);
-                std_hash::Hash::hash(&loc1.2, hasher);
-
-                // Do not hash the file name twice
-                std_hash::Hash::hash(&loc2.1, hasher);
-                std_hash::Hash::hash(&loc2.2, hasher);
-            } else {
-                std_hash::Hash::hash(&1u8, hasher);
-
-                std_hash::Hash::hash(loc1.0, hasher);
-                std_hash::Hash::hash(&loc1.1, hasher);
-                std_hash::Hash::hash(&loc1.2, hasher);
-
-                std_hash::Hash::hash(loc2.0, hasher);
-                std_hash::Hash::hash(&loc2.1, hasher);
-                std_hash::Hash::hash(&loc2.2, hasher);
+        if span.hi < span.lo {
+            return std_hash::Hash::hash(&TAG_INVALID_SPAN, hasher);
+        }
+
+        let (file_lo, line_lo, col_lo) = match hcx.codemap()
+                                                  .byte_pos_to_line_and_col(span.lo) {
+            Some(pos) => pos,
+            None => {
+                return std_hash::Hash::hash(&TAG_INVALID_SPAN, hasher);
             }
+        };
+
+        if !file_lo.contains(span.hi) {
+            return std_hash::Hash::hash(&TAG_INVALID_SPAN, hasher);
         }
 
+        let len = span.hi - span.lo;
+
+        std_hash::Hash::hash(&TAG_VALID_SPAN, hasher);
+        std_hash::Hash::hash(&file_lo.name, hasher);
+        std_hash::Hash::hash(&line_lo, hasher);
+        std_hash::Hash::hash(&col_lo, hasher);
+        std_hash::Hash::hash(&len, hasher);
+
         if span.ctxt == SyntaxContext::empty() {
-            0u8.hash_stable(hcx, hasher);
+            TAG_NO_EXPANSION.hash_stable(hcx, hasher);
         } else {
-            1u8.hash_stable(hcx, hasher);
-            self.source_callsite().hash_stable(hcx, hasher);
+            TAG_EXPANSION.hash_stable(hcx, hasher);
+            span.ctxt.outer().expn_info().hash_stable(hcx, hasher);
         }
     }
 }

src/librustc/ich/impls_syntax.rs

@@ -347,6 +347,30 @@ impl_stable_hash_for!(enum ::syntax::ast::MetaItemKind {
     NameValue(lit)
 });
 
+impl_stable_hash_for!(struct ::syntax_pos::hygiene::ExpnInfo {
+    call_site,
+    callee
+});
+
+impl_stable_hash_for!(struct ::syntax_pos::hygiene::NameAndSpan {
+    format,
+    allow_internal_unstable,
+    allow_internal_unsafe,
+    span
+});
+
+impl_stable_hash_for!(enum ::syntax_pos::hygiene::ExpnFormat {
+    MacroAttribute(sym),
+    MacroBang(sym),
+    CompilerDesugaring(kind)
+});
+
+impl_stable_hash_for!(enum ::syntax_pos::hygiene::CompilerDesugaringKind {
+    BackArrow,
+    DotFill,
+    QuestionMark
+});
+
 impl<'gcx> HashStable<StableHashingContext<'gcx>> for FileMap {
     fn hash_stable<W: StableHasherResult>(&self,
                                           hcx: &mut StableHashingContext<'gcx>,

src/librustc/ty/context.rs

@@ -1235,7 +1235,7 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
                                            -> Result<(), E::Error>
         where E: ty::codec::TyEncoder
     {
-        self.on_disk_query_result_cache.serialize(self.global_tcx(), self.cstore, encoder)
+        self.on_disk_query_result_cache.serialize(self.global_tcx(), encoder)
     }
 
 }

src/librustc/ty/maps/config.rs

@@ -31,9 +31,9 @@ pub(super) trait QueryDescription<'tcx>: QueryConfig {
         false
     }
 
-    fn load_from_disk<'a>(_: TyCtxt<'a, 'tcx, 'tcx>,
+    fn try_load_from_disk(_: TyCtxt<'_, 'tcx, 'tcx>,
                           _: SerializedDepNodeIndex)
-                          -> Self::Value {
+                          -> Option<Self::Value> {
         bug!("QueryDescription::load_from_disk() called for unsupport query.")
     }
 }
@@ -556,12 +556,14 @@ impl<'tcx> QueryDescription<'tcx> for queries::typeck_tables_of<'tcx> {
         def_id.is_local()
     }
 
-    fn load_from_disk<'a>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
+    fn try_load_from_disk(tcx: TyCtxt<'_, 'tcx, 'tcx>,
                           id: SerializedDepNodeIndex)
-                          -> Self::Value {
-        let typeck_tables: ty::TypeckTables<'tcx> = tcx.on_disk_query_result_cache
-                                                       .load_query_result(tcx, id);
-        tcx.alloc_tables(typeck_tables)
+                          -> Option<Self::Value> {
+        let typeck_tables: Option<ty::TypeckTables<'tcx>> = tcx
+            .on_disk_query_result_cache
+            .try_load_query_result(tcx, id);
+
+        typeck_tables.map(|tables| tcx.alloc_tables(tables))
     }
 }