Merge from rustc

4 files changed, 87 insertions, 13 deletions

diff --git a/compiler/rustc_errors/Cargo.toml b/compiler/rustc_errors/Cargo.toml
index fbb6a1cc475..b11793c190a 100644
--- a/compiler/rustc_errors/Cargo.toml
+++ b/compiler/rustc_errors/Cargo.toml
@@ -1,7 +1,7 @@
 [package]
 name = "rustc_errors"
 version = "0.0.0"
-edition = "2021"
+edition = "2024"
 
 [dependencies]
 # tidy-alphabetical-start
@@ -10,10 +10,12 @@ derive_setters = "0.1.6"
 rustc_abi = { path = "../rustc_abi" }
 rustc_ast = { path = "../rustc_ast" }
 rustc_ast_pretty = { path = "../rustc_ast_pretty" }
+rustc_attr_data_structures = { path = "../rustc_attr_data_structures" }
 rustc_data_structures = { path = "../rustc_data_structures" }
 rustc_error_codes = { path = "../rustc_error_codes" }
 rustc_error_messages = { path = "../rustc_error_messages" }
 rustc_fluent_macro = { path = "../rustc_fluent_macro" }
+rustc_hashes = { path = "../rustc_hashes" }
 rustc_hir = { path = "../rustc_hir" }
 rustc_index = { path = "../rustc_index" }
 rustc_lexer = { path = "../rustc_lexer" }
diff --git a/compiler/rustc_errors/src/diagnostic_impls.rs b/compiler/rustc_errors/src/diagnostic_impls.rs
index d179396398f..db6532f41ea 100644
--- a/compiler/rustc_errors/src/diagnostic_impls.rs
+++ b/compiler/rustc_errors/src/diagnostic_impls.rs
@@ -8,6 +8,7 @@ use std::process::ExitStatus;
 use rustc_abi::TargetDataLayoutErrors;
 use rustc_ast::util::parser::ExprPrecedence;
 use rustc_ast_pretty::pprust;
+use rustc_attr_data_structures::RustcVersion;
 use rustc_macros::Subdiagnostic;
 use rustc_span::edition::Edition;
 use rustc_span::{Ident, MacroRulesNormalizedIdent, Span, Symbol};
@@ -93,8 +94,15 @@ into_diag_arg_using_display!(
     SplitDebuginfo,
     ExitStatus,
     ErrCode,
+    rustc_abi::ExternAbi,
 );
 
+impl IntoDiagArg for RustcVersion {
+    fn into_diag_arg(self) -> DiagArgValue {
+        DiagArgValue::Str(Cow::Owned(self.to_string()))
+    }
+}
+
 impl<I: rustc_type_ir::Interner> IntoDiagArg for rustc_type_ir::TraitRef<I> {
     fn into_diag_arg(self) -> DiagArgValue {
         self.to_string().into_diag_arg()
@@ -108,13 +116,13 @@ impl<I: rustc_type_ir::Interner> IntoDiagArg for rustc_type_ir::ExistentialTrait
 }
 
 impl<I: rustc_type_ir::Interner> IntoDiagArg for rustc_type_ir::UnevaluatedConst<I> {
-    fn into_diag_arg(self) -> rustc_errors::DiagArgValue {
+    fn into_diag_arg(self) -> DiagArgValue {
         format!("{self:?}").into_diag_arg()
     }
 }
 
 impl<I: rustc_type_ir::Interner> IntoDiagArg for rustc_type_ir::FnSig<I> {
-    fn into_diag_arg(self) -> rustc_errors::DiagArgValue {
+    fn into_diag_arg(self) -> DiagArgValue {
         format!("{self:?}").into_diag_arg()
     }
 }
diff --git a/compiler/rustc_errors/src/emitter.rs b/compiler/rustc_errors/src/emitter.rs
index 15cf285e7ff..f7f84239308 100644
--- a/compiler/rustc_errors/src/emitter.rs
+++ b/compiler/rustc_errors/src/emitter.rs
@@ -1976,13 +1976,16 @@ impl HumanEmitter {
             Some(Style::HeaderMsg),
         );
 
+        let other_suggestions = suggestions.len().saturating_sub(MAX_SUGGESTIONS);
+
         let mut row_num = 2;
         for (i, (complete, parts, highlights, _)) in
-            suggestions.iter().enumerate().take(MAX_SUGGESTIONS)
+            suggestions.into_iter().enumerate().take(MAX_SUGGESTIONS)
         {
             debug!(?complete, ?parts, ?highlights);
 
-            let has_deletion = parts.iter().any(|p| p.is_deletion(sm));
+            let has_deletion =
+                parts.iter().any(|p| p.is_deletion(sm) || p.is_destructive_replacement(sm));
             let is_multiline = complete.lines().count() > 1;
 
             if i == 0 {
@@ -2167,7 +2170,7 @@ impl HumanEmitter {
                 self.draw_code_line(
                     &mut buffer,
                     &mut row_num,
-                    highlight_parts,
+                    &highlight_parts,
                     line_pos + line_start,
                     line,
                     show_code_change,
@@ -2376,9 +2379,12 @@ impl HumanEmitter {
                 row_num = row + 1;
             }
         }
-        if suggestions.len() > MAX_SUGGESTIONS {
-            let others = suggestions.len() - MAX_SUGGESTIONS;
-            let msg = format!("and {} other candidate{}", others, pluralize!(others));
+        if other_suggestions > 0 {
+            let msg = format!(
+                "and {} other candidate{}",
+                other_suggestions,
+                pluralize!(other_suggestions)
+            );
             buffer.puts(row_num, max_line_num_len + 3, &msg, Style::NoStyle);
         }
 
diff --git a/compiler/rustc_errors/src/lib.rs b/compiler/rustc_errors/src/lib.rs
index 9af17db9a6e..f2b133f5677 100644
--- a/compiler/rustc_errors/src/lib.rs
+++ b/compiler/rustc_errors/src/lib.rs
@@ -15,7 +15,6 @@
 #![feature(box_into_inner)]
 #![feature(box_patterns)]
 #![feature(error_reporter)]
-#![feature(extract_if)]
 #![feature(if_let_guard)]
 #![feature(let_chains)]
 #![feature(negative_impls)]
@@ -58,19 +57,20 @@ pub use emitter::ColorConfig;
 use emitter::{DynEmitter, Emitter, is_case_difference, is_different};
 use rustc_data_structures::AtomicRef;
 use rustc_data_structures::fx::{FxHashSet, FxIndexMap, FxIndexSet};
-use rustc_data_structures::stable_hasher::{Hash128, StableHasher};
+use rustc_data_structures::stable_hasher::StableHasher;
 use rustc_data_structures::sync::{DynSend, Lock};
 pub use rustc_error_messages::{
     DiagMessage, FluentBundle, LanguageIdentifier, LazyFallbackBundle, MultiSpan, SpanLabel,
     SubdiagMessage, fallback_fluent_bundle, fluent_bundle,
 };
+use rustc_hashes::Hash128;
 use rustc_lint_defs::LintExpectationId;
 pub use rustc_lint_defs::{Applicability, listify, pluralize};
 use rustc_macros::{Decodable, Encodable};
 pub use rustc_span::ErrorGuaranteed;
 pub use rustc_span::fatal_error::{FatalError, FatalErrorMarker};
 use rustc_span::source_map::SourceMap;
-use rustc_span::{DUMMY_SP, Loc, Span};
+use rustc_span::{BytePos, DUMMY_SP, Loc, Span};
 pub use snippet::Style;
 // Used by external projects such as `rust-gpu`.
 // See https://github.com/rust-lang/rust/pull/115393.
@@ -230,10 +230,63 @@ impl SubstitutionPart {
         !self.snippet.is_empty() && self.replaces_meaningful_content(sm)
     }
 
+    /// Whether this is a replacement that overwrites source with a snippet
+    /// in a way that isn't a superset of the original string. For example,
+    /// replacing "abc" with "abcde" is not destructive, but replacing it
+    /// it with "abx" is, since the "c" character is lost.
+    pub fn is_destructive_replacement(&self, sm: &SourceMap) -> bool {
+        self.is_replacement(sm)
+            && !sm
+                .span_to_snippet(self.span)
+                .is_ok_and(|snippet| as_substr(snippet.trim(), self.snippet.trim()).is_some())
+    }
+
     fn replaces_meaningful_content(&self, sm: &SourceMap) -> bool {
         sm.span_to_snippet(self.span)
             .map_or(!self.span.is_empty(), |snippet| !snippet.trim().is_empty())
     }
+
+    /// Try to turn a replacement into an addition when the span that is being
+    /// overwritten matches either the prefix or suffix of the replacement.
+    fn trim_trivial_replacements(&mut self, sm: &SourceMap) {
+        if self.snippet.is_empty() {
+            return;
+        }
+        let Ok(snippet) = sm.span_to_snippet(self.span) else {
+            return;
+        };
+
+        if let Some((prefix, substr, suffix)) = as_substr(&snippet, &self.snippet) {
+            self.span = Span::new(
+                self.span.lo() + BytePos(prefix as u32),
+                self.span.hi() - BytePos(suffix as u32),
+                self.span.ctxt(),
+                self.span.parent(),
+            );
+            self.snippet = substr.to_string();
+        }
+    }
+}
+
+/// Given an original string like `AACC`, and a suggestion like `AABBCC`, try to detect
+/// the case where a substring of the suggestion is "sandwiched" in the original, like
+/// `BB` is. Return the length of the prefix, the "trimmed" suggestion, and the length
+/// of the suffix.
+fn as_substr<'a>(original: &'a str, suggestion: &'a str) -> Option<(usize, &'a str, usize)> {
+    let common_prefix = original
+        .chars()
+        .zip(suggestion.chars())
+        .take_while(|(c1, c2)| c1 == c2)
+        .map(|(c, _)| c.len_utf8())
+        .sum();
+    let original = &original[common_prefix..];
+    let suggestion = &suggestion[common_prefix..];
+    if suggestion.ends_with(original) {
+        let common_suffix = original.len();
+        Some((common_prefix, &suggestion[..suggestion.len() - original.len()], common_suffix))
+    } else {
+        None
+    }
 }
 
 impl CodeSuggestion {
@@ -349,7 +402,12 @@ impl CodeSuggestion {
                 // or deleted code in order to point at the correct column *after* substitution.
                 let mut acc = 0;
                 let mut only_capitalization = false;
-                for part in &substitution.parts {
+                for part in &mut substitution.parts {
+                    // If this is a replacement of, e.g. `"a"` into `"ab"`, adjust the
+                    // suggestion and snippet to look as if we just suggested to add
+                    // `"b"`, which is typically much easier for the user to understand.
+                    part.trim_trivial_replacements(sm);
+
                     only_capitalization |= is_case_difference(sm, &part.snippet, part.span);
                     let cur_lo = sm.lookup_char_pos(part.span.lo());
                     if prev_hi.line == cur_lo.line {