Shorten trimmed display of closures

When `with_forced_trimmed_paths` is used, only print filename and start
of the closure's span, to reduce their verbosity.

Author: estebank

compiler/rustc_middle/src/ty/print/pretty.rs

@@ -16,6 +16,7 @@ use rustc_session::config::TrimmedDefPaths;
 use rustc_session::cstore::{ExternCrate, ExternCrateSource};
 use rustc_session::Limit;
 use rustc_span::symbol::{kw, Ident, Symbol};
+use rustc_span::FileNameDisplayPreference;
 use rustc_target::abi::Size;
 use rustc_target::spec::abi::Abi;
 use smallvec::SmallVec;
@@ -818,11 +819,16 @@ pub trait PrettyPrinter<'tcx>:
                             p!("@", print_def_path(did.to_def_id(), substs));
                         } else {
                             let span = self.tcx().def_span(did);
+                            let preference = if FORCE_TRIMMED_PATH.with(|flag| flag.get()) {
+                                FileNameDisplayPreference::Short
+                            } else {
+                                FileNameDisplayPreference::Remapped
+                            };
                             p!(write(
                                 "@{}",
                                 // This may end up in stderr diagnostics but it may also be emitted
                                 // into MIR. Hence we use the remapped path if available
-                                self.tcx().sess.source_map().span_to_embeddable_string(span)
+                                self.tcx().sess.source_map().span_to_string(span, preference)
                             ));
                         }
                     } else {

compiler/rustc_span/src/lib.rs

@@ -259,6 +259,10 @@ impl RealFileName {
             FileNameDisplayPreference::Remapped => {
                 self.remapped_path_if_available().to_string_lossy()
             }
+            FileNameDisplayPreference::Short => self
+                .local_path_if_available()
+                .file_name()
+                .map_or_else(|| "".into(), |f| f.to_string_lossy()),
         }
     }
 }
@@ -302,6 +306,9 @@ pub enum FileNameDisplayPreference {
     /// Display the path before the application of rewrite rules provided via `--remap-path-prefix`.
     /// This is appropriate for use in user-facing output (such as diagnostics).
     Local,
+    /// Display only the filename, as a way to reduce the verbosity of the output.
+    /// This is appropriate for use in user-facing output (such as diagnostics).
+    Short,
 }
 
 pub struct FileNameDisplay<'a> {

compiler/rustc_span/src/source_map.rs

@@ -438,20 +438,27 @@ impl SourceMap {
         }
     }
 
-    fn span_to_string(&self, sp: Span, filename_display_pref: FileNameDisplayPreference) -> String {
+    pub fn span_to_string(
+        &self,
+        sp: Span,
+        filename_display_pref: FileNameDisplayPreference,
+    ) -> String {
         if self.files.borrow().source_files.is_empty() || sp.is_dummy() {
             return "no-location".to_string();
         }
 
         let lo = self.lookup_char_pos(sp.lo());
         let hi = self.lookup_char_pos(sp.hi());
         format!(
-            "{}:{}:{}: {}:{}",
+            "{}:{}:{}{}",
             lo.file.name.display(filename_display_pref),
             lo.line,
             lo.col.to_usize() + 1,
-            hi.line,
-            hi.col.to_usize() + 1,
+            if let FileNameDisplayPreference::Short = filename_display_pref {
+                String::new()
+            } else {
+                format!(": {}:{}", hi.line, hi.col.to_usize() + 1)
+            }
         )
     }
 

src/test/ui/higher-rank-trait-bounds/issue-62203-hrtb-ice.stderr

@@ -30,7 +30,7 @@ LL |     where
 LL |         F: for<'r> T0<'r, (<Self as Ty<'r>>::V,), O = <B as Ty<'r>>::V>,
    |                                                   ^^^^^^^^^^^^^^^^^^^^ required by this bound in `T1::m`
 
-error[E0271]: expected `[closure@$DIR/issue-62203-hrtb-ice.rs:42:16: 42:19]` to be a closure that returns `Unit3`, but it returns `Unit4`
+error[E0271]: expected `[closure@issue-62203-hrtb-ice.rs:42:16]` to be a closure that returns `Unit3`, but it returns `Unit4`
   --> $DIR/issue-62203-hrtb-ice.rs:39:9
    |
 LL |       let v = Unit2.m(

src/test/ui/issues/issue-31173.stderr

@@ -1,4 +1,4 @@
-error[E0271]: expected `TakeWhile<&mut IntoIter<u8>, [closure@$DIR/issue-31173.rs:7:21: 7:25]>` to be an iterator that yields `&_`, but it yields `u8`
+error[E0271]: expected `TakeWhile<&mut IntoIter<u8>, [closure@issue-31173.rs:7:21]>` to be an iterator that yields `&_`, but it yields `u8`
   --> $DIR/issue-31173.rs:11:10
    |
 LL |         .cloned()

src/test/ui/never_type/fallback-closure-wrap.fallback.stderr

@@ -1,4 +1,4 @@
-error[E0271]: expected `[closure@$DIR/fallback-closure-wrap.rs:18:40: 18:47]` to be a closure that returns `()`, but it returns `!`
+error[E0271]: expected `[closure@fallback-closure-wrap.rs:18:40]` to be a closure that returns `()`, but it returns `!`
   --> $DIR/fallback-closure-wrap.rs:18:31
    |
 LL |       let error = Closure::wrap(Box::new(move || {