Auto merge of #79957 - jyn514:smaller-span, r=GuillaumeGomez

[rustdoc] Calculate span information on demand instead of storing it ahead of time

This brings `size_of<clean::types::Span>()` down from over 100 bytes (!!) to only 12, the same as rustc. It brings `Item` down even more, from `784` to `680`.

~~TODO: I need to figure out how to do this for the JSON backend too. That uses `From` impls everywhere, which don't allow passing in the `Session` as an argument. `@P1n3appl3,` `@tmandry,` maybe one of you have ideas?~~ Figured it out, fortunately only two functions needed to be changed. I like the `convert_x()` format better than `From` everywhere but I'm open to feedback.

Helps with #79103

src/librustdoc/clean/auto_trait.rs

@@ -118,7 +118,7 @@ impl<'a, 'tcx> AutoTraitFinder<'a, 'tcx> {
                 };
 
                 Some(Item {
-                    source: Span::empty(),
+                    source: Span::dummy(),
                     name: None,
                     attrs: Default::default(),
                     visibility: Inherited,

src/librustdoc/clean/inline.rs

@@ -479,7 +479,7 @@ fn build_module(cx: &DocContext<'_>, did: DefId, visited: &mut FxHashSet<DefId>)
                     items.push(clean::Item {
                         name: None,
                         attrs: clean::Attributes::default(),
-                        source: clean::Span::empty(),
+                        source: clean::Span::dummy(),
                         def_id: DefId::local(CRATE_DEF_INDEX),
                         visibility: clean::Public,
                         stability: None,

src/librustdoc/clean/mod.rs

@@ -25,7 +25,7 @@ use rustc_middle::ty::{self, AdtKind, Lift, Ty, TyCtxt};
 use rustc_mir::const_eval::{is_const_fn, is_min_const_fn, is_unstable_const_fn};
 use rustc_span::hygiene::{AstPass, MacroKind};
 use rustc_span::symbol::{kw, sym, Ident, Symbol};
-use rustc_span::{self, ExpnKind, Pos};
+use rustc_span::{self, ExpnKind};
 use rustc_typeck::hir_ty_to_ty;
 
 use std::collections::hash_map::Entry;
@@ -1881,29 +1881,8 @@ impl Clean<VariantKind> for hir::VariantData<'_> {
 }
 
 impl Clean<Span> for rustc_span::Span {
-    fn clean(&self, cx: &DocContext<'_>) -> Span {
-        if self.is_dummy() {
-            return Span::empty();
-        }
-
-        // Get the macro invocation instead of the definition,
-        // in case the span is result of a macro expansion.
-        // (See rust-lang/rust#39726)
-        let span = self.source_callsite();
-
-        let sm = cx.sess().source_map();
-        let filename = sm.span_to_filename(span);
-        let lo = sm.lookup_char_pos(span.lo());
-        let hi = sm.lookup_char_pos(span.hi());
-        Span {
-            filename,
-            cnum: lo.file.cnum,
-            loline: lo.line,
-            locol: lo.col.to_usize(),
-            hiline: hi.line,
-            hicol: hi.col.to_usize(),
-            original: span,
-        }
+    fn clean(&self, _cx: &DocContext<'_>) -> Span {
+        Span::from_rustc_span(*self)
     }
 }
 

src/librustdoc/clean/types.rs

@@ -17,15 +17,16 @@ use rustc_data_structures::fx::{FxHashMap, FxHashSet};
 use rustc_feature::UnstableFeatures;
 use rustc_hir as hir;
 use rustc_hir::def::Res;
-use rustc_hir::def_id::{CrateNum, DefId, LOCAL_CRATE};
+use rustc_hir::def_id::{CrateNum, DefId};
 use rustc_hir::lang_items::LangItem;
 use rustc_hir::Mutability;
 use rustc_index::vec::IndexVec;
 use rustc_middle::ty::{AssocKind, TyCtxt};
+use rustc_session::Session;
 use rustc_span::hygiene::MacroKind;
 use rustc_span::source_map::DUMMY_SP;
 use rustc_span::symbol::{kw, sym, Ident, Symbol, SymbolStr};
-use rustc_span::{self, FileName};
+use rustc_span::{self, FileName, Loc};
 use rustc_target::abi::VariantIdx;
 use rustc_target::spec::abi::Abi;
 use smallvec::{smallvec, SmallVec};
@@ -1609,32 +1610,41 @@ crate enum VariantKind {
     Struct(VariantStruct),
 }
 
+/// Small wrapper around `rustc_span::Span` that adds helper methods and enforces calling `source_callsite`.
 #[derive(Clone, Debug)]
-crate struct Span {
-    crate filename: FileName,
-    crate cnum: CrateNum,
-    crate loline: usize,
-    crate locol: usize,
-    crate hiline: usize,
-    crate hicol: usize,
-    crate original: rustc_span::Span,
-}
+crate struct Span(rustc_span::Span);
 
 impl Span {
-    crate fn empty() -> Span {
-        Span {
-            filename: FileName::Anon(0),
-            cnum: LOCAL_CRATE,
-            loline: 0,
-            locol: 0,
-            hiline: 0,
-            hicol: 0,
-            original: rustc_span::DUMMY_SP,
-        }
+    crate fn from_rustc_span(sp: rustc_span::Span) -> Self {
+        // Get the macro invocation instead of the definition,
+        // in case the span is result of a macro expansion.
+        // (See rust-lang/rust#39726)
+        Self(sp.source_callsite())
+    }
+
+    crate fn dummy() -> Self {
+        Self(rustc_span::DUMMY_SP)
     }
 
     crate fn span(&self) -> rustc_span::Span {
-        self.original
+        self.0
+    }
+
+    crate fn filename(&self, sess: &Session) -> FileName {
+        sess.source_map().span_to_filename(self.0)
+    }
+
+    crate fn lo(&self, sess: &Session) -> Loc {
+        sess.source_map().lookup_char_pos(self.0.lo())
+    }
+
+    crate fn hi(&self, sess: &Session) -> Loc {
+        sess.source_map().lookup_char_pos(self.0.hi())
+    }
+
+    crate fn cnum(&self, sess: &Session) -> CrateNum {
+        // FIXME: is there a time when the lo and hi crate would be different?
+        self.lo(sess).file.cnum
     }
 }
 

src/librustdoc/formats/renderer.rs

@@ -1,5 +1,7 @@
 use std::sync::Arc;
 
+use rustc_data_structures::sync::Lrc;
+use rustc_session::Session;
 use rustc_span::edition::Edition;
 
 use crate::clean;
@@ -19,6 +21,7 @@ crate trait FormatRenderer: Clone {
         render_info: RenderInfo,
         edition: Edition,
         cache: &mut Cache,
+        sess: Lrc<Session>,
     ) -> Result<(Self, clean::Crate), Error>;
 
     /// Renders a single non-module item. This means no recursive sub-item rendering is required.
@@ -49,6 +52,7 @@ crate fn run_format<T: FormatRenderer>(
     render_info: RenderInfo,
     diag: &rustc_errors::Handler,
     edition: Edition,
+    sess: Lrc<Session>,
 ) -> Result<(), Error> {
     let (krate, mut cache) = Cache::from_krate(
         render_info.clone(),
@@ -59,7 +63,7 @@ crate fn run_format<T: FormatRenderer>(
     );
 
     let (mut format_renderer, mut krate) =
-        T::init(krate, options, render_info, edition, &mut cache)?;
+        T::init(krate, options, render_info, edition, &mut cache, sess)?;
 
     let cache = Arc::new(cache);
     // Freeze the cache now that the index has been built. Put an Arc into TLS for future

src/librustdoc/html/render/mod.rs

@@ -52,10 +52,12 @@ use rustc_ast_pretty::pprust;
 use rustc_attr::StabilityLevel;
 use rustc_data_structures::flock;
 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
+use rustc_data_structures::sync::Lrc;
 use rustc_hir as hir;
 use rustc_hir::def_id::{DefId, LOCAL_CRATE};
 use rustc_hir::Mutability;
 use rustc_middle::middle::stability;
+use rustc_session::Session;
 use rustc_span::edition::Edition;
 use rustc_span::hygiene::MacroKind;
 use rustc_span::source_map::FileName;
@@ -121,6 +123,7 @@ crate struct Context {
 }
 
 crate struct SharedContext {
+    crate sess: Lrc<Session>,
     /// The path to the crate root source minus the file name.
     /// Used for simplifying paths to the highlighted source code files.
     crate src_root: PathBuf,
@@ -171,6 +174,10 @@ impl Context {
         let filename = format!("{}{}.{}", base, self.shared.resource_suffix, ext);
         self.dst.join(&filename)
     }
+
+    fn sess(&self) -> &Session {
+        &self.shared.sess
+    }
 }
 
 impl SharedContext {
@@ -381,6 +388,7 @@ impl FormatRenderer for Context {
         _render_info: RenderInfo,
         edition: Edition,
         cache: &mut Cache,
+        sess: Lrc<Session>,
     ) -> Result<(Context, clean::Crate), Error> {
         // need to save a copy of the options for rendering the index page
         let md_opts = options.clone();
@@ -453,6 +461,7 @@ impl FormatRenderer for Context {
         }
         let (sender, receiver) = channel();
         let mut scx = SharedContext {
+            sess,
             collapsed: krate.collapsed,
             src_root,
             include_sources,
@@ -1629,24 +1638,24 @@ impl Context {
     /// of their crate documentation isn't known.
     fn src_href(&self, item: &clean::Item, cache: &Cache) -> Option<String> {
         let mut root = self.root_path();
-
         let mut path = String::new();
+        let cnum = item.source.cnum(self.sess());
 
         // We can safely ignore synthetic `SourceFile`s.
-        let file = match item.source.filename {
+        let file = match item.source.filename(self.sess()) {
             FileName::Real(ref path) => path.local_path().to_path_buf(),
             _ => return None,
         };
         let file = &file;
 
-        let (krate, path) = if item.source.cnum == LOCAL_CRATE {
+        let (krate, path) = if cnum == LOCAL_CRATE {
             if let Some(path) = self.shared.local_sources.get(file) {
                 (&self.shared.layout.krate, path)
             } else {
                 return None;
             }
         } else {
-            let (krate, src_root) = match *cache.extern_locations.get(&item.source.cnum)? {
+            let (krate, src_root) = match *cache.extern_locations.get(&cnum)? {
                 (ref name, ref src, ExternalLocation::Local) => (name, src),
                 (ref name, ref src, ExternalLocation::Remote(ref s)) => {
                     root = s.to_string();
@@ -1665,11 +1674,10 @@ impl Context {
             (krate, &path)
         };
 
-        let lines = if item.source.loline == item.source.hiline {
-            item.source.loline.to_string()
-        } else {
-            format!("{}-{}", item.source.loline, item.source.hiline)
-        };
+        let loline = item.source.lo(self.sess()).line;
+        let hiline = item.source.hi(self.sess()).line;
+        let lines =
+            if loline == hiline { loline.to_string() } else { format!("{}-{}", loline, hiline) };
         Some(format!(
             "{root}src/{krate}/{path}#{lines}",
             root = Escape(&root),

src/librustdoc/html/sources.rs

@@ -7,6 +7,7 @@ use crate::html::highlight;
 use crate::html::layout;
 use crate::html::render::{SharedContext, BASIC_KEYWORDS};
 use rustc_hir::def_id::LOCAL_CRATE;
+use rustc_session::Session;
 use rustc_span::source_map::FileName;
 use std::ffi::OsStr;
 use std::fs;
@@ -34,37 +35,45 @@ struct SourceCollector<'a> {
 
 impl<'a> DocFolder for SourceCollector<'a> {
     fn fold_item(&mut self, item: clean::Item) -> Option<clean::Item> {
+        // If we're not rendering sources, there's nothing to do.
         // If we're including source files, and we haven't seen this file yet,
         // then we need to render it out to the filesystem.
         if self.scx.include_sources
             // skip all synthetic "files"
-            && item.source.filename.is_real()
+            && item.source.filename(self.sess()).is_real()
             // skip non-local files
-            && item.source.cnum == LOCAL_CRATE
+            && item.source.cnum(self.sess()) == LOCAL_CRATE
         {
+            let filename = item.source.filename(self.sess());
             // If it turns out that we couldn't read this file, then we probably
             // can't read any of the files (generating html output from json or
             // something like that), so just don't include sources for the
             // entire crate. The other option is maintaining this mapping on a
             // per-file basis, but that's probably not worth it...
-            self.scx.include_sources = match self.emit_source(&item.source.filename) {
+            self.scx.include_sources = match self.emit_source(&filename) {
                 Ok(()) => true,
                 Err(e) => {
                     println!(
                         "warning: source code was requested to be rendered, \
                          but processing `{}` had an error: {}",
-                        item.source.filename, e
+                        filename, e
                     );
                     println!("         skipping rendering of source code");
                     false
                 }
             };
         }
+        // FIXME: if `include_sources` isn't set and DocFolder didn't require consuming the crate by value,
+        // we could return None here without having to walk the rest of the crate.
         Some(self.fold_item_recur(item))
     }
 }
 
 impl<'a> SourceCollector<'a> {
+    fn sess(&self) -> &Session {
+        &self.scx.sess
+    }
+
     /// Renders the given filename into its corresponding HTML source file.
     fn emit_source(&mut self, filename: &FileName) -> Result<(), Error> {
         let p = match *filename {

src/librustdoc/json/conversions.rs

@@ -6,14 +6,16 @@ use std::convert::From;
 
 use rustc_ast::ast;
 use rustc_span::def_id::{DefId, CRATE_DEF_INDEX};
+use rustc_span::Pos;
 
 use crate::clean;
 use crate::doctree;
 use crate::formats::item_type::ItemType;
 use crate::json::types::*;
+use crate::json::JsonRenderer;
 
-impl From<clean::Item> for Option<Item> {
-    fn from(item: clean::Item) -> Self {
+impl JsonRenderer {
+    pub(super) fn convert_item(&self, item: clean::Item) -> Option<Item> {
         let item_type = ItemType::from(&item);
         let clean::Item {
             source,
@@ -32,7 +34,7 @@ impl From<clean::Item> for Option<Item> {
                 id: def_id.into(),
                 crate_id: def_id.krate.as_u32(),
                 name,
-                source: source.into(),
+                source: self.convert_span(source),
                 visibility: visibility.into(),
                 docs: attrs.collapsed_doc_value().unwrap_or_default(),
                 links: attrs
@@ -53,22 +55,23 @@ impl From<clean::Item> for Option<Item> {
             }),
         }
     }
-}
 
-impl From<clean::Span> for Option<Span> {
-    fn from(span: clean::Span) -> Self {
-        let clean::Span { loline, locol, hiline, hicol, .. } = span;
-        match span.filename {
-            rustc_span::FileName::Real(name) => Some(Span {
-                filename: match name {
-                    rustc_span::RealFileName::Named(path) => path,
-                    rustc_span::RealFileName::Devirtualized { local_path, virtual_name: _ } => {
-                        local_path
-                    }
-                },
-                begin: (loline, locol),
-                end: (hiline, hicol),
-            }),
+    fn convert_span(&self, span: clean::Span) -> Option<Span> {
+        match span.filename(&self.sess) {
+            rustc_span::FileName::Real(name) => {
+                let hi = span.hi(&self.sess);
+                let lo = span.lo(&self.sess);
+                Some(Span {
+                    filename: match name {
+                        rustc_span::RealFileName::Named(path) => path,
+                        rustc_span::RealFileName::Devirtualized { local_path, virtual_name: _ } => {
+                            local_path
+                        }
+                    },
+                    begin: (lo.line, lo.col.to_usize()),
+                    end: (hi.line, hi.col.to_usize()),
+                })
+            }
             _ => None,
         }
     }