Auto merge of #84176 - GuillaumeGomez:src-to-definition, r=jyn514

Generate links to definition in rustdoc source code pages

## Description

This PR adds an option (disabled by default) to add links in the source code page on ident. So for for example:

```rust
mod other_module;
struct Foo;
fn bar() {}

fn x<T: other_module::Trait>(f: Foo, g: other_module::Whatever, t: &T) {
    let f: Foo = Foo;
    bar();
    f.some_method();
}
```

In the example (mostly in the `x` function), `other_module::Trait`, `Foo`, `other_module::Whatever`, `bar` and `some_method` are now links (and `other_module` at the top too).

In case there is a type coming from another crate, it'll link to its documentation page and not its definition (but you can then click on `[src]` so I guess it's fine).

Another important detail: I voluntarily didn't add links for primitive types. I think we can discuss about adding links on them or not in a later PR (adding the support for them would require only a few lines).

Here is a video summing up everything I wrote above:

https://user-images.githubusercontent.com/3050060/114622354-21307b00-9cae-11eb-834d-f6d8178a37bd.mp4

## Performance impact

So, on my computer, the performance remains more or less the same (which is quite surprising but that's a nice surprise). Here are the numbers:

Without the option:
 * core:  1m 21s
 * alloc: 26.78s
 * std: 27.30s
 * proc_macro: 4.50s

With source to definition links generation (I enabled by default the option):
 * core: 1m 25s
 * alloc: 25.76s
 * std: 27.07s
 * proc_macro: 4.66s

So no real change here (again, I'm very surprised by this fact).

For the size of the generated source files (only taking into account the `src` folder here since it's the only one impacted) by running `du -shc .` (when I am in the source folder).

Without the option: 11.939 MB
With the option: 12.611 MB

So not a big change here either. In all those docs, I ran `grep -nR '<a class=' . | wc -l` and got 43917. So there are quite a lot of links added. :)

cc `@rust-lang/rustdoc`
r? `@jyn514`

compiler/rustc_errors/src/lib.rs

@@ -342,6 +342,9 @@ struct HandlerInner {
     deduplicated_warn_count: usize,
 
     future_breakage_diagnostics: Vec<Diagnostic>,
+
+    /// If set to `true`, no warning or error will be emitted.
+    quiet: bool,
 }
 
 /// A key denoting where from a diagnostic was stashed.
@@ -456,10 +459,19 @@ impl Handler {
                 emitted_diagnostics: Default::default(),
                 stashed_diagnostics: Default::default(),
                 future_breakage_diagnostics: Vec::new(),
+                quiet: false,
             }),
         }
     }
 
+    pub fn with_disabled_diagnostic<T, F: FnOnce() -> T>(&self, f: F) -> T {
+        let prev = self.inner.borrow_mut().quiet;
+        self.inner.borrow_mut().quiet = true;
+        let ret = f();
+        self.inner.borrow_mut().quiet = prev;
+        ret
+    }
+
     // This is here to not allow mutation of flags;
     // as of this writing it's only used in tests in librustc_middle.
     pub fn can_emit_warnings(&self) -> bool {
@@ -818,7 +830,7 @@ impl HandlerInner {
     }
 
     fn emit_diagnostic(&mut self, diagnostic: &Diagnostic) {
-        if diagnostic.cancelled() {
+        if diagnostic.cancelled() || self.quiet {
             return;
         }
 
@@ -1035,6 +1047,9 @@ impl HandlerInner {
     }
 
     fn delay_as_bug(&mut self, diagnostic: Diagnostic) {
+        if self.quiet {
+            return;
+        }
         if self.flags.report_delayed_bugs {
             self.emit_diagnostic(&diagnostic);
         }

compiler/rustc_session/src/session.rs

@@ -500,6 +500,10 @@ impl Session {
         &self.parse_sess.span_diagnostic
     }
 
+    pub fn with_disabled_diagnostic<T, F: FnOnce() -> T>(&self, f: F) -> T {
+        self.parse_sess.span_diagnostic.with_disabled_diagnostic(f)
+    }
+
     /// Analogous to calling methods on the given `DiagnosticBuilder`, but
     /// deduplicates on lint ID, span (if any), and message for this `Session`
     fn diag_once<'a, 'b>(

src/librustdoc/clean/blanket_impl.rs

@@ -98,7 +98,7 @@ impl<'a, 'tcx> BlanketImplFinder<'a, 'tcx> {
                     visibility: Inherited,
                     def_id: ItemId::Blanket { impl_id: impl_def_id, for_: item_def_id },
                     kind: box ImplItem(Impl {
-                        span: Span::from_rustc_span(self.cx.tcx.def_span(impl_def_id)),
+                        span: Span::new(self.cx.tcx.def_span(impl_def_id)),
                         unsafety: hir::Unsafety::Normal,
                         generics: (
                             self.cx.tcx.generics_of(impl_def_id),

src/librustdoc/clean/inline.rs

@@ -517,7 +517,7 @@ fn build_module(
         }
     }
 
-    let span = clean::Span::from_rustc_span(cx.tcx.def_span(did));
+    let span = clean::Span::new(cx.tcx.def_span(did));
     clean::Module { items, span }
 }
 

src/librustdoc/clean/mod.rs

@@ -95,7 +95,8 @@ impl Clean<Item> for doctree::Module<'_> {
 
         // determine if we should display the inner contents or
         // the outer `mod` item for the source code.
-        let span = Span::from_rustc_span({
+
+        let span = Span::new({
             let where_outer = self.where_outer(cx.tcx);
             let sm = cx.sess().source_map();
             let outer = sm.lookup_char_pos(where_outer.lo());

src/librustdoc/clean/types.rs

@@ -343,7 +343,7 @@ crate struct Item {
 rustc_data_structures::static_assert_size!(Item, 56);
 
 crate fn rustc_span(def_id: DefId, tcx: TyCtxt<'_>) -> Span {
-    Span::from_rustc_span(def_id.as_local().map_or_else(
+    Span::new(def_id.as_local().map_or_else(
         || tcx.def_span(def_id),
         |local| {
             let hir = tcx.hir();
@@ -1943,10 +1943,11 @@ crate enum Variant {
 crate struct Span(rustc_span::Span);
 
 impl Span {
-    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)
+    /// Wraps a [`rustc_span::Span`]. In case this span is the result of a macro expansion, the
+    /// span will be updated to point to the macro invocation instead of the macro definition.
+    ///
+    /// (See rust-lang/rust#39726)
+    crate fn new(sp: rustc_span::Span) -> Self {
         Self(sp.source_callsite())
     }
 

src/librustdoc/config.rs

@@ -276,6 +276,8 @@ crate struct RenderOptions {
     crate show_type_layout: bool,
     crate unstable_features: rustc_feature::UnstableFeatures,
     crate emit: Vec<EmitType>,
+    /// If `true`, HTML source pages will generate links for items to their definition.
+    crate generate_link_to_definition: bool,
 }
 
 #[derive(Copy, Clone, Debug, PartialEq, Eq)]
@@ -655,6 +657,15 @@ impl Options {
         let generate_redirect_map = matches.opt_present("generate-redirect-map");
         let show_type_layout = matches.opt_present("show-type-layout");
         let nocapture = matches.opt_present("nocapture");
+        let generate_link_to_definition = matches.opt_present("generate-link-to-definition");
+
+        if generate_link_to_definition && (show_coverage || output_format != OutputFormat::Html) {
+            diag.struct_err(
+                "--generate-link-to-definition option can only be used with HTML output format",
+            )
+            .emit();
+            return Err(1);
+        }
 
         let (lint_opts, describe_lints, lint_cap) =
             get_cmd_lint_options(matches, error_format, &debugging_opts);
@@ -721,6 +732,7 @@ impl Options {
                     crate_name.as_deref(),
                 ),
                 emit,
+                generate_link_to_definition,
             },
             crate_name,
             output_format,

src/librustdoc/html/format.rs

@@ -484,7 +484,11 @@ crate enum HrefError {
     NotInExternalCache,
 }
 
-crate fn href(did: DefId, cx: &Context<'_>) -> Result<(String, ItemType, Vec<String>), HrefError> {
+crate fn href_with_root_path(
+    did: DefId,
+    cx: &Context<'_>,
+    root_path: Option<&str>,
+) -> Result<(String, ItemType, Vec<String>), HrefError> {
     let cache = &cx.cache();
     let relative_to = &cx.current;
     fn to_module_fqp(shortty: ItemType, fqp: &[String]) -> &[String] {
@@ -495,6 +499,7 @@ crate fn href(did: DefId, cx: &Context<'_>) -> Result<(String, ItemType, Vec<Str
         return Err(HrefError::Private);
     }
 
+    let mut is_remote = false;
     let (fqp, shortty, mut url_parts) = match cache.paths.get(&did) {
         Some(&(ref fqp, shortty)) => (fqp, shortty, {
             let module_fqp = to_module_fqp(shortty, fqp);
@@ -508,6 +513,7 @@ crate fn href(did: DefId, cx: &Context<'_>) -> Result<(String, ItemType, Vec<Str
                     shortty,
                     match cache.extern_locations[&did.krate] {
                         ExternalLocation::Remote(ref s) => {
+                            is_remote = true;
                             let s = s.trim_end_matches('/');
                             let mut s = vec![s];
                             s.extend(module_fqp[..].iter().map(String::as_str));
@@ -522,6 +528,12 @@ crate fn href(did: DefId, cx: &Context<'_>) -> Result<(String, ItemType, Vec<Str
             }
         }
     };
+    if !is_remote {
+        if let Some(root_path) = root_path {
+            let root = root_path.trim_end_matches('/');
+            url_parts.insert(0, root);
+        }
+    }
     let last = &fqp.last().unwrap()[..];
     let filename;
     match shortty {
@@ -536,6 +548,10 @@ crate fn href(did: DefId, cx: &Context<'_>) -> Result<(String, ItemType, Vec<Str
     Ok((url_parts.join("/"), shortty, fqp.to_vec()))
 }
 
+crate fn href(did: DefId, cx: &Context<'_>) -> Result<(String, ItemType, Vec<String>), HrefError> {
+    href_with_root_path(did, cx, None)
+}
+
 /// Both paths should only be modules.
 /// This is because modules get their own directories; that is, `std::vec` and `std::vec::Vec` will
 /// both need `../iter/trait.Iterator.html` to get at the iterator trait.