Auto merge of #73996 - da-x:short-unique-paths, r=petrochenkov

diagnostics: shorten paths of unique symbols

This is a step towards implementing a fix for #50310, and continuation of the discussion in [Pre-RFC: Nicer Types In Diagnostics - compiler - Rust Internals](https://internals.rust-lang.org/t/pre-rfc-nicer-types-in-diagnostics/11139). Impressed upon me from previous discussion in #21934 that an RFC for this is not needed, and I should just come up with code.

The recent improvements to `use` suggestions that I've contributed have given rise to this implementation. Contrary to previous suggestions, it's rather simple logic, and I believe it only reduces the amount of cognitive load that a developer would need when reading type errors.

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If a symbol name can only be imported from one place, and as long as it was not glob-imported anywhere in the current crate, we can trim its printed path to the last component.

This has wide implications on error messages with types, for example, shortening `std::vec::Vec` to just `Vec`, as long as there is no other `Vec` importable from anywhere.

1 files changed, 11 insertions, 8 deletions

diff --git a/compiler/rustc_codegen_ssa/src/mir/block.rs b/compiler/rustc_codegen_ssa/src/mir/block.rs
index 6eb80157239..d448fa165e0 100644
--- a/compiler/rustc_codegen_ssa/src/mir/block.rs
+++ b/compiler/rustc_codegen_ssa/src/mir/block.rs
@@ -16,6 +16,7 @@ use rustc_middle::mir;
 use rustc_middle::mir::interpret::{AllocId, ConstValue, Pointer, Scalar};
 use rustc_middle::mir::AssertKind;
 use rustc_middle::ty::layout::{FnAbiExt, HasTyCtxt};
+use rustc_middle::ty::print::with_no_trimmed_paths;
 use rustc_middle::ty::{self, Instance, Ty, TypeFoldable};
 use rustc_span::source_map::Span;
 use rustc_span::{sym, Symbol};
@@ -479,14 +480,16 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                 UninitValid => !layout.might_permit_raw_init(bx, /*zero:*/ false).unwrap(),
             };
             if do_panic {
-                let msg_str = if layout.abi.is_uninhabited() {
-                    // Use this error even for the other intrinsics as it is more precise.
-                    format!("attempted to instantiate uninhabited type `{}`", ty)
-                } else if intrinsic == ZeroValid {
-                    format!("attempted to zero-initialize type `{}`, which is invalid", ty)
-                } else {
-                    format!("attempted to leave type `{}` uninitialized, which is invalid", ty)
-                };
+                let msg_str = with_no_trimmed_paths(|| {
+                    if layout.abi.is_uninhabited() {
+                        // Use this error even for the other intrinsics as it is more precise.
+                        format!("attempted to instantiate uninhabited type `{}`", ty)
+                    } else if intrinsic == ZeroValid {
+                        format!("attempted to zero-initialize type `{}`, which is invalid", ty)
+                    } else {
+                        format!("attempted to leave type `{}` uninitialized, which is invalid", ty)
+                    }
+                });
                 let msg = bx.const_str(Symbol::intern(&msg_str));
                 let location = self.get_caller_location(bx, span).immediate();