Auto merge of rust-lang#137030 - matthiaskrgr:rollup-267aumr, r=matth…

…iaskrgr

Rollup of 9 pull requests

Successful merges:

 - rust-lang#135778 (account for `c_enum_min_bits` in `multiple-reprs` UI test)
 - rust-lang#136052 (Correct comment for FreeBSD and DragonFly BSD in unix/thread)
 - rust-lang#136886 (Remove the common prelude module)
 - rust-lang#136956 (add vendor directory to .gitignore)
 - rust-lang#136958 (Fix presentation of purely "additive" replacement suggestion parts)
 - rust-lang#136967 (Use `slice::fill` in `io::Repeat` implementation)
 - rust-lang#136976 (alloc boxed: docs: use MaybeUninit::write instead of as_mut_ptr)
 - rust-lang#137007 (Emit MIR for each bit with on `dont_reset_cast_kind_without_updating_operand`)
 - rust-lang#137008 (Move code into `rustc_mir_transform`)

r? `@ghost`
`@rustbot` modify labels: rollup

.gitignore

@@ -54,6 +54,8 @@ no_llvm_build
 /library/target
 /src/bootstrap/target
 /src/tools/x/target
+# Created by `x vendor`
+/vendor
 # Created by default with `src/ci/docker/run.sh`
 /obj/
 # Created by nix dev shell / .envrc

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) || p.is_replacement(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,
@@ -2213,7 +2216,12 @@ impl HumanEmitter {
             if let DisplaySuggestion::Diff | DisplaySuggestion::Underline | DisplaySuggestion::Add =
                 show_code_change
             {
-                for part in parts {
+                for mut part in 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);
+
                     let snippet = if let Ok(snippet) = sm.span_to_snippet(part.span) {
                         snippet
                     } else {
@@ -2376,9 +2384,12 @@ 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);
         }
 

compiler/rustc_errors/src/lib.rs

@@ -230,10 +230,40 @@ 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| {
+                self.snippet.trim_start().starts_with(snippet.trim_start())
+                    || self.snippet.trim_end().ends_with(snippet.trim_end())
+            })
+    }
+
     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 self.snippet.starts_with(&snippet) {
+            self.span = self.span.shrink_to_hi();
+            self.snippet = self.snippet[snippet.len()..].to_string();
+        } else if self.snippet.ends_with(&snippet) {
+            self.span = self.span.shrink_to_lo();
+            self.snippet = self.snippet[..self.snippet.len() - snippet.len()].to_string();
+        }
+    }
 }
 
 impl CodeSuggestion {

compiler/rustc_middle/src/mir/mod.rs

@@ -49,7 +49,6 @@ pub mod generic_graphviz;
 pub mod graphviz;
 pub mod interpret;
 pub mod mono;
-pub mod patch;
 pub mod pretty;
 mod query;
 mod statement;

compiler/rustc_mir_dataflow/src/drop_flag_effects.rs

@@ -3,7 +3,26 @@ use rustc_middle::mir::{self, Body, Location, Terminator, TerminatorKind};
 use tracing::debug;
 
 use super::move_paths::{InitKind, LookupResult, MoveData, MovePathIndex};
-use crate::elaborate_drops::DropFlagState;
+
+/// The value of an inserted drop flag.
+#[derive(Debug, PartialEq, Eq, Copy, Clone)]
+pub enum DropFlagState {
+    /// The tracked value is initialized and needs to be dropped when leaving its scope.
+    Present,
+
+    /// The tracked value is uninitialized or was moved out of and does not need to be dropped when
+    /// leaving its scope.
+    Absent,
+}
+
+impl DropFlagState {
+    pub fn value(self) -> bool {
+        match self {
+            DropFlagState::Present => true,
+            DropFlagState::Absent => false,
+        }
+    }
+}
 
 pub fn move_path_children_matching<'tcx, F>(
     move_data: &MoveData<'tcx>,

compiler/rustc_mir_dataflow/src/impls/initialized.rs

@@ -9,7 +9,7 @@ use rustc_middle::ty::util::Discr;
 use rustc_middle::ty::{self, TyCtxt};
 use tracing::{debug, instrument};
 
-use crate::elaborate_drops::DropFlagState;
+use crate::drop_flag_effects::DropFlagState;
 use crate::framework::SwitchIntTarget;
 use crate::move_paths::{HasMoveData, InitIndex, InitKind, LookupResult, MoveData, MovePathIndex};
 use crate::{

compiler/rustc_mir_dataflow/src/lib.rs

@@ -15,7 +15,7 @@ use rustc_middle::ty;
 // Please change the public `use` directives cautiously, as they might be used by external tools.
 // See issue #120130.
 pub use self::drop_flag_effects::{
-    drop_flag_effects_for_function_entry, drop_flag_effects_for_location,
+    DropFlagState, drop_flag_effects_for_function_entry, drop_flag_effects_for_location,
     move_path_children_matching, on_all_children_bits, on_lookup_result_bits,
 };
 pub use self::framework::{
@@ -26,7 +26,6 @@ use self::move_paths::MoveData;
 
 pub mod debuginfo;
 mod drop_flag_effects;
-pub mod elaborate_drops;
 mod errors;
 mod framework;
 pub mod impls;

compiler/rustc_mir_transform/src/add_moves_for_packed_drops.rs

@@ -1,8 +1,8 @@
-use rustc_middle::mir::patch::MirPatch;
 use rustc_middle::mir::*;
 use rustc_middle::ty::{self, TyCtxt};
 use tracing::debug;
 
+use crate::patch::MirPatch;
 use crate::util;
 
 /// This pass moves values being dropped that are within a packed

compiler/rustc_mir_transform/src/add_subtyping_projections.rs

@@ -1,8 +1,9 @@
-use rustc_middle::mir::patch::MirPatch;
 use rustc_middle::mir::visit::MutVisitor;
 use rustc_middle::mir::*;
 use rustc_middle::ty::TyCtxt;
 
+use crate::patch::MirPatch;
+
 pub(super) struct Subtyper;
 
 struct SubTypeChecker<'a, 'tcx> {

compiler/rustc_mir_transform/src/coroutine.rs

@@ -1061,9 +1061,8 @@ fn insert_switch<'tcx>(
 }
 
 fn elaborate_coroutine_drops<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
-    use rustc_middle::mir::patch::MirPatch;
-    use rustc_mir_dataflow::elaborate_drops::{Unwind, elaborate_drop};
-
+    use crate::elaborate_drop::{Unwind, elaborate_drop};
+    use crate::patch::MirPatch;
     use crate::shim::DropShimElaborator;
 
     // Note that `elaborate_drops` only drops the upvars of a coroutine, and

compiler/rustc_mir_transform/src/deref_separator.rs

@@ -1,9 +1,10 @@
-use rustc_middle::mir::patch::MirPatch;
 use rustc_middle::mir::visit::NonUseContext::VarDebugInfo;
 use rustc_middle::mir::visit::{MutVisitor, PlaceContext};
 use rustc_middle::mir::*;
 use rustc_middle::ty::TyCtxt;
 
+use crate::patch::MirPatch;
+
 pub(super) struct Derefer;
 
 struct DerefChecker<'a, 'tcx> {

compiler/rustc_mir_transform/src/early_otherwise_branch.rs

@@ -1,11 +1,11 @@
 use std::fmt::Debug;
 
-use rustc_middle::mir::patch::MirPatch;
 use rustc_middle::mir::*;
 use rustc_middle::ty::{Ty, TyCtxt};
 use tracing::trace;
 
 use super::simplify::simplify_cfg;
+use crate::patch::MirPatch;
 
 /// This pass optimizes something like
 /// ```ignore (syntax-highlighting-only)

compiler/rustc_mir_transform/src/elaborate_box_derefs.rs

@@ -4,12 +4,13 @@
 
 use rustc_abi::FieldIdx;
 use rustc_hir::def_id::DefId;
-use rustc_middle::mir::patch::MirPatch;
 use rustc_middle::mir::visit::MutVisitor;
 use rustc_middle::mir::*;
 use rustc_middle::span_bug;
 use rustc_middle::ty::{Ty, TyCtxt};
 
+use crate::patch::MirPatch;
+
 /// Constructs the types used when accessing a Box's pointer
 fn build_ptr_tys<'tcx>(
     tcx: TyCtxt<'tcx>,

compiler/rustc_mir_dataflow/src/elaborate_drops.rs → compiler/rustc_mir_transform/src/elaborate_drop.rs

@@ -3,7 +3,6 @@ use std::{fmt, iter, mem};
 use rustc_abi::{FIRST_VARIANT, FieldIdx, VariantIdx};
 use rustc_hir::lang_items::LangItem;
 use rustc_index::Idx;
-use rustc_middle::mir::patch::MirPatch;
 use rustc_middle::mir::*;
 use rustc_middle::span_bug;
 use rustc_middle::ty::adjustment::PointerCoercion;
@@ -13,29 +12,11 @@ use rustc_span::DUMMY_SP;
 use rustc_span::source_map::Spanned;
 use tracing::{debug, instrument};
 
-/// The value of an inserted drop flag.
-#[derive(Debug, PartialEq, Eq, Copy, Clone)]
-pub enum DropFlagState {
-    /// The tracked value is initialized and needs to be dropped when leaving its scope.
-    Present,
-
-    /// The tracked value is uninitialized or was moved out of and does not need to be dropped when
-    /// leaving its scope.
-    Absent,
-}
-
-impl DropFlagState {
-    pub fn value(self) -> bool {
-        match self {
-            DropFlagState::Present => true,
-            DropFlagState::Absent => false,
-        }
-    }
-}
+use crate::patch::MirPatch;
 
 /// Describes how/if a value should be dropped.
 #[derive(Debug)]
-pub enum DropStyle {
+pub(crate) enum DropStyle {
     /// The value is already dead at the drop location, no drop will be executed.
     Dead,
 
@@ -56,7 +37,7 @@ pub enum DropStyle {
 
 /// Which drop flags to affect/check with an operation.
 #[derive(Debug)]
-pub enum DropFlagMode {
+pub(crate) enum DropFlagMode {
     /// Only affect the top-level drop flag, not that of any contained fields.
     Shallow,
     /// Affect all nested drop flags in addition to the top-level one.
@@ -65,7 +46,7 @@ pub enum DropFlagMode {
 
 /// Describes if unwinding is necessary and where to unwind to if a panic occurs.
 #[derive(Copy, Clone, Debug)]
-pub enum Unwind {
+pub(crate) enum Unwind {
     /// Unwind to this block.
     To(BasicBlock),
     /// Already in an unwind path, any panic will cause an abort.
@@ -98,7 +79,7 @@ impl Unwind {
     }
 }
 
-pub trait DropElaborator<'a, 'tcx>: fmt::Debug {
+pub(crate) trait DropElaborator<'a, 'tcx>: fmt::Debug {
     /// The type representing paths that can be moved out of.
     ///
     /// Users can move out of individual fields of a struct, such as `a.b.c`. This type is used to
@@ -177,7 +158,7 @@ where
 /// value.
 ///
 /// When this returns, the MIR patch in the `elaborator` contains the necessary changes.
-pub fn elaborate_drop<'b, 'tcx, D>(
+pub(crate) fn elaborate_drop<'b, 'tcx, D>(
     elaborator: &mut D,
     source_info: SourceInfo,
     place: Place<'tcx>,

compiler/rustc_mir_transform/src/elaborate_drops.rs

@@ -3,21 +3,20 @@ use std::fmt;
 use rustc_abi::{FieldIdx, VariantIdx};
 use rustc_index::IndexVec;
 use rustc_index::bit_set::DenseBitSet;
-use rustc_middle::mir::patch::MirPatch;
 use rustc_middle::mir::*;
 use rustc_middle::ty::{self, TyCtxt};
-use rustc_mir_dataflow::elaborate_drops::{
-    DropElaborator, DropFlagMode, DropFlagState, DropStyle, Unwind, elaborate_drop,
-};
 use rustc_mir_dataflow::impls::{MaybeInitializedPlaces, MaybeUninitializedPlaces};
 use rustc_mir_dataflow::move_paths::{LookupResult, MoveData, MovePathIndex};
 use rustc_mir_dataflow::{
-    Analysis, MoveDataTypingEnv, ResultsCursor, on_all_children_bits, on_lookup_result_bits,
+    Analysis, DropFlagState, MoveDataTypingEnv, ResultsCursor, on_all_children_bits,
+    on_lookup_result_bits,
 };
 use rustc_span::Span;
 use tracing::{debug, instrument};
 
 use crate::deref_separator::deref_finder;
+use crate::elaborate_drop::{DropElaborator, DropFlagMode, DropStyle, Unwind, elaborate_drop};
+use crate::patch::MirPatch;
 
 /// During MIR building, Drop terminators are inserted in every place where a drop may occur.
 /// However, in this phase, the presence of these terminators does not guarantee that a destructor

compiler/rustc_mir_transform/src/lib.rs

@@ -49,10 +49,12 @@ mod check_pointers;
 mod cost_checker;
 mod cross_crate_inline;
 mod deduce_param_attrs;
+mod elaborate_drop;
 mod errors;
 mod ffi_unwind_calls;
 mod lint;
 mod lint_tail_expr_drop_order;
+mod patch;
 mod shim;
 mod ssa;
 

compiler/rustc_mir_transform/src/match_branches.rs

@@ -2,14 +2,14 @@ use std::iter;
 
 use rustc_abi::Integer;
 use rustc_index::IndexSlice;
-use rustc_middle::mir::patch::MirPatch;
 use rustc_middle::mir::*;
 use rustc_middle::ty::layout::{IntegerExt, TyAndLayout};
 use rustc_middle::ty::{self, ScalarInt, Ty, TyCtxt};
 use rustc_type_ir::TyKind::*;
 use tracing::instrument;
 
 use super::simplify::simplify_cfg;
+use crate::patch::MirPatch;
 
 pub(super) struct MatchBranchSimplification;