Auto merge of #16451 - Urhengulas:satisfy-clippy, r=Veykril

internal: Work through temporarily allowed clippy lints, part 2

Another follow-up to https://github.com/rust-lang/rust-analyzer/pull/16401.

39 files changed, 136 insertions, 149 deletions

diff --git a/Cargo.toml b/Cargo.toml
index d5f9740c6de..5a748648116 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -167,29 +167,14 @@ new_ret_no_self = "allow"
 
 ## Following lints should be tackled at some point
 borrowed_box = "allow"
-borrow_deref_ref = "allow"
-derivable_impls = "allow"
 derived_hash_with_manual_eq = "allow"
-field_reassign_with_default = "allow"
 forget_non_drop = "allow"
-format_collect = "allow"
-large_enum_variant = "allow"
 needless_doctest_main = "allow"
-new_without_default = "allow"
 non_canonical_clone_impl = "allow"
 non_canonical_partial_ord_impl = "allow"
 self_named_constructors = "allow"
-skip_while_next = "allow"
 too_many_arguments = "allow"
-toplevel_ref_arg = "allow"
 type_complexity = "allow"
-unnecessary_cast = "allow"
-unnecessary_filter_map = "allow"
-unnecessary_lazy_evaluations = "allow"
-unnecessary_mut_passed = "allow"
-useless_conversion = "allow"
-useless_format = "allow"
-wildcard_in_or_patterns = "allow"
 wrong_self_convention = "allow"
 
 ## warn at following lints
diff --git a/crates/flycheck/src/lib.rs b/crates/flycheck/src/lib.rs
index 68faca51e82..22603842a1b 100644
--- a/crates/flycheck/src/lib.rs
+++ b/crates/flycheck/src/lib.rs
@@ -493,7 +493,9 @@ impl CargoActor {
                     // Skip certain kinds of messages to only spend time on what's useful
                     JsonMessage::Cargo(message) => match message {
                         cargo_metadata::Message::CompilerArtifact(artifact) if !artifact.fresh => {
-                            self.sender.send(CargoMessage::CompilerArtifact(artifact)).unwrap();
+                            self.sender
+                                .send(CargoMessage::CompilerArtifact(Box::new(artifact)))
+                                .unwrap();
                         }
                         cargo_metadata::Message::CompilerMessage(msg) => {
                             self.sender.send(CargoMessage::Diagnostic(msg.message)).unwrap();
@@ -538,7 +540,7 @@ impl CargoActor {
 }
 
 enum CargoMessage {
-    CompilerArtifact(cargo_metadata::Artifact),
+    CompilerArtifact(Box<cargo_metadata::Artifact>),
     Diagnostic(Diagnostic),
 }
 
diff --git a/crates/hir-def/src/body/pretty.rs b/crates/hir-def/src/body/pretty.rs
index 0f2b279670c..b821b91b895 100644
--- a/crates/hir-def/src/body/pretty.rs
+++ b/crates/hir-def/src/body/pretty.rs
@@ -33,7 +33,7 @@ pub(super) fn print_body_hir(db: &dyn DefDatabase, body: &Body, owner: DefWithBo
                 }
             )
         }),
-        DefWithBodyId::InTypeConstId(_) => format!("In type const = "),
+        DefWithBodyId::InTypeConstId(_) => "In type const = ".to_string(),
         DefWithBodyId::VariantId(it) => {
             let loc = it.lookup(db);
             let enum_loc = loc.parent.lookup(db);
diff --git a/crates/hir-def/src/body/tests.rs b/crates/hir-def/src/body/tests.rs
index a76ddffb411..a27ffe21675 100644
--- a/crates/hir-def/src/body/tests.rs
+++ b/crates/hir-def/src/body/tests.rs
@@ -256,7 +256,7 @@ impl SsrError {
 "##,
     );
 
-    assert_eq!(db.body_with_source_map(def.into()).1.diagnostics(), &[]);
+    assert_eq!(db.body_with_source_map(def).1.diagnostics(), &[]);
     expect![[r#"
         fn main() {
             _ = $crate::error::SsrError::new(
@@ -309,7 +309,7 @@ fn f() {
 "#,
     );
 
-    let (_, source_map) = db.body_with_source_map(def.into());
+    let (_, source_map) = db.body_with_source_map(def);
     assert_eq!(source_map.diagnostics(), &[]);
 
     for (_, def_map) in body.blocks(&db) {
diff --git a/crates/hir-def/src/data.rs b/crates/hir-def/src/data.rs
index 73fbad5e675..7ce05b64d02 100644
--- a/crates/hir-def/src/data.rs
+++ b/crates/hir-def/src/data.rs
@@ -782,7 +782,7 @@ impl<'a> AssocItemCollector<'a> {
             self.diagnostics.push(DefDiagnostic::macro_expansion_parse_error(
                 self.module_id.local_id,
                 error_call_kind(),
-                errors.into(),
+                errors,
             ));
         }
 
diff --git a/crates/hir-def/src/hir/format_args.rs b/crates/hir-def/src/hir/format_args.rs
index 113f9441a01..b097a721c75 100644
--- a/crates/hir-def/src/hir/format_args.rs
+++ b/crates/hir-def/src/hir/format_args.rs
@@ -166,6 +166,7 @@ enum PositionUsedAs {
 }
 use PositionUsedAs::*;
 
+#[allow(clippy::unnecessary_lazy_evaluations)]
 pub(crate) fn parse(
     s: &ast::String,
     fmt_snippet: Option<String>,
@@ -177,9 +178,9 @@ pub(crate) fn parse(
     let text = s.text_without_quotes();
     let str_style = match s.quote_offsets() {
         Some(offsets) => {
-            let raw = u32::from(offsets.quotes.0.len()) - 1;
+            let raw = usize::from(offsets.quotes.0.len()) - 1;
             // subtract 1 for the `r` prefix
-            (raw != 0).then(|| raw as usize - 1)
+            (raw != 0).then(|| raw - 1)
         }
         None => None,
     };
@@ -432,7 +433,7 @@ pub(crate) fn parse(
     }
 }
 
-#[derive(Debug, Clone, PartialEq, Eq)]
+#[derive(Clone, Debug, Default, Eq, PartialEq)]
 pub struct FormatArgumentsCollector {
     arguments: Vec<FormatArgument>,
     num_unnamed_args: usize,
@@ -451,7 +452,7 @@ impl FormatArgumentsCollector {
     }
 
     pub fn new() -> Self {
-        Self { arguments: vec![], names: vec![], num_unnamed_args: 0, num_explicit_args: 0 }
+        Default::default()
     }
 
     pub fn add(&mut self, arg: FormatArgument) -> usize {
diff --git a/crates/hir-def/src/import_map.rs b/crates/hir-def/src/import_map.rs
index 66d9cf54daa..c698510ca99 100644
--- a/crates/hir-def/src/import_map.rs
+++ b/crates/hir-def/src/import_map.rs
@@ -297,7 +297,7 @@ impl SearchMode {
             SearchMode::Exact => candidate.eq_ignore_ascii_case(query),
             SearchMode::Prefix => {
                 query.len() <= candidate.len() && {
-                    let prefix = &candidate[..query.len() as usize];
+                    let prefix = &candidate[..query.len()];
                     if case_sensitive {
                         prefix == query
                     } else {
@@ -396,7 +396,7 @@ impl Query {
 pub fn search_dependencies(
     db: &dyn DefDatabase,
     krate: CrateId,
-    ref query: Query,
+    query: &Query,
 ) -> FxHashSet<ItemInNs> {
     let _p = tracing::span!(tracing::Level::INFO, "search_dependencies", ?query).entered();
 
@@ -446,7 +446,7 @@ fn search_maps(
             let end = (value & 0xFFFF_FFFF) as usize;
             let start = (value >> 32) as usize;
             let ImportMap { item_to_info_map, importables, .. } = &*import_maps[import_map_idx];
-            let importables = &importables[start as usize..end];
+            let importables = &importables[start..end];
 
             let iter = importables
                 .iter()
@@ -516,7 +516,7 @@ mod tests {
             })
             .expect("could not find crate");
 
-        let actual = search_dependencies(db.upcast(), krate, query)
+        let actual = search_dependencies(db.upcast(), krate, &query)
             .into_iter()
             .filter_map(|dependency| {
                 let dependency_krate = dependency.krate(db.upcast())?;
diff --git a/crates/hir-def/src/macro_expansion_tests/mod.rs b/crates/hir-def/src/macro_expansion_tests/mod.rs
index ec299405387..e315414e9bd 100644
--- a/crates/hir-def/src/macro_expansion_tests/mod.rs
+++ b/crates/hir-def/src/macro_expansion_tests/mod.rs
@@ -25,7 +25,7 @@ use hir_expand::{
     InFile, MacroFileId, MacroFileIdExt,
 };
 use span::Span;
-use stdx::format_to;
+use stdx::{format_to, format_to_acc};
 use syntax::{
     ast::{self, edit::IndentLevel},
     AstNode,
@@ -149,8 +149,7 @@ pub fn identity_when_valid(_attr: TokenStream, item: TokenStream) -> TokenStream
         if tree {
             let tree = format!("{:#?}", parse.syntax_node())
                 .split_inclusive('\n')
-                .map(|line| format!("// {line}"))
-                .collect::<String>();
+                .fold(String::new(), |mut acc, line| format_to_acc!(acc, "// {line}"));
             format_to!(expn_text, "\n{}", tree)
         }
         let range = call.syntax().text_range();
diff --git a/crates/hir-def/src/nameres/collector.rs b/crates/hir-def/src/nameres/collector.rs
index bdef9c8a931..fb6fd867a16 100644
--- a/crates/hir-def/src/nameres/collector.rs
+++ b/crates/hir-def/src/nameres/collector.rs
@@ -1924,7 +1924,7 @@ impl ModCollector<'_, '_> {
                         item_tree: self.item_tree,
                         mod_dir,
                     }
-                    .collect_in_top_module(&*items);
+                    .collect_in_top_module(items);
                     if is_macro_use {
                         self.import_all_legacy_macros(module_id);
                     }
diff --git a/crates/hir-def/src/nameres/path_resolution.rs b/crates/hir-def/src/nameres/path_resolution.rs
index 2c7e2227913..70da0ef8e1e 100644
--- a/crates/hir-def/src/nameres/path_resolution.rs
+++ b/crates/hir-def/src/nameres/path_resolution.rs
@@ -475,7 +475,7 @@ impl DefMap {
         let macro_use_prelude = || {
             self.macro_use_prelude.get(name).map_or(PerNs::none(), |&(it, _extern_crate)| {
                 PerNs::macros(
-                    it.into(),
+                    it,
                     Visibility::Public,
                     // FIXME?
                     None, // extern_crate.map(ImportOrExternCrate::ExternCrate),
diff --git a/crates/hir-def/src/per_ns.rs b/crates/hir-def/src/per_ns.rs
index 6a62ef69701..36ab62d0f7f 100644
--- a/crates/hir-def/src/per_ns.rs
+++ b/crates/hir-def/src/per_ns.rs
@@ -16,19 +16,13 @@ pub enum Namespace {
     Macros,
 }
 
-#[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
+#[derive(Clone, Copy, Debug, Default, Eq, Hash, PartialEq)]
 pub struct PerNs {
     pub types: Option<(ModuleDefId, Visibility, Option<ImportOrExternCrate>)>,
     pub values: Option<(ModuleDefId, Visibility, Option<ImportId>)>,
     pub macros: Option<(MacroId, Visibility, Option<ImportId>)>,
 }
 
-impl Default for PerNs {
-    fn default() -> Self {
-        PerNs { types: None, values: None, macros: None }
-    }
-}
-
 impl PerNs {
     pub fn none() -> PerNs {
         PerNs { types: None, values: None, macros: None }
@@ -131,13 +125,11 @@ impl PerNs {
             .into_iter()
             .chain(
                 self.values
-                    .map(|it| (ItemInNs::Values(it.0), it.2.map(ImportOrExternCrate::Import)))
-                    .into_iter(),
+                    .map(|it| (ItemInNs::Values(it.0), it.2.map(ImportOrExternCrate::Import))),
             )
             .chain(
                 self.macros
-                    .map(|it| (ItemInNs::Macros(it.0), it.2.map(ImportOrExternCrate::Import)))
-                    .into_iter(),
+                    .map(|it| (ItemInNs::Macros(it.0), it.2.map(ImportOrExternCrate::Import))),
             )
     }
 }
diff --git a/crates/hir-def/src/test_db.rs b/crates/hir-def/src/test_db.rs
index c992c3c9204..9edb03c7cab 100644
--- a/crates/hir-def/src/test_db.rs
+++ b/crates/hir-def/src/test_db.rs
@@ -41,13 +41,13 @@ impl Default for TestDB {
 
 impl Upcast<dyn ExpandDatabase> for TestDB {
     fn upcast(&self) -> &(dyn ExpandDatabase + 'static) {
-        &*self
+        self
     }
 }
 
 impl Upcast<dyn DefDatabase> for TestDB {
     fn upcast(&self) -> &(dyn DefDatabase + 'static) {
-        &*self
+        self
     }
 }
 
diff --git a/crates/hir-expand/src/attrs.rs b/crates/hir-expand/src/attrs.rs
index b0b2501ce9d..c20c1639e1a 100644
--- a/crates/hir-expand/src/attrs.rs
+++ b/crates/hir-expand/src/attrs.rs
@@ -230,7 +230,7 @@ impl Attr {
                     )
                 )
             })
-            .unwrap_or_else(|| tt.len());
+            .unwrap_or(tt.len());
 
         let (path, input) = tt.split_at(path_end);
         let path = Interned::new(ModPath::from_tt(db, path)?);
diff --git a/crates/hir-ty/src/inhabitedness.rs b/crates/hir-ty/src/inhabitedness.rs
index a63556f450d..532b650e8ff 100644
--- a/crates/hir-ty/src/inhabitedness.rs
+++ b/crates/hir-ty/src/inhabitedness.rs
@@ -84,8 +84,7 @@ impl TypeVisitor<Interner> for UninhabitedFrom<'_> {
                 Some(0) | None => CONTINUE_OPAQUELY_INHABITED,
                 Some(1..) => item_ty.super_visit_with(self, outer_binder),
             },
-
-            TyKind::Ref(..) | _ => CONTINUE_OPAQUELY_INHABITED,
+            _ => CONTINUE_OPAQUELY_INHABITED,
         };
         self.recursive_ty.remove(ty);
         self.max_depth += 1;
diff --git a/crates/hir-ty/src/mir/lower/pattern_matching.rs b/crates/hir-ty/src/mir/lower/pattern_matching.rs
index 65ab12929dd..8202bac532f 100644
--- a/crates/hir-ty/src/mir/lower/pattern_matching.rs
+++ b/crates/hir-ty/src/mir/lower/pattern_matching.rs
@@ -114,7 +114,7 @@ impl MirLowerCtx<'_> {
                             index: i as u32,
                         }))
                     }),
-                    &mut cond_place,
+                    &cond_place,
                     mode,
                 )?
             }
diff --git a/crates/hir-ty/src/utils.rs b/crates/hir-ty/src/utils.rs
index c6e238ff8be..c0ca9d713ca 100644
--- a/crates/hir-ty/src/utils.rs
+++ b/crates/hir-ty/src/utils.rs
@@ -440,7 +440,7 @@ pub(crate) fn detect_variant_from_bytes<'a>(
             (db.enum_data(e).variants[index.0].0, layout)
         }
         hir_def::layout::Variants::Multiple { tag, tag_encoding, variants, .. } => {
-            let size = tag.size(&*target_data_layout).bytes_usize();
+            let size = tag.size(target_data_layout).bytes_usize();
             let offset = layout.fields.offset(0).bytes_usize(); // The only field on enum variants is the tag field
             let tag = i128::from_le_bytes(pad16(&b[offset..offset + size], false));
             match tag_encoding {
diff --git a/crates/hir/src/attrs.rs b/crates/hir/src/attrs.rs
index f2b9db669e0..5c369f42e6e 100644
--- a/crates/hir/src/attrs.rs
+++ b/crates/hir/src/attrs.rs
@@ -239,10 +239,9 @@ fn resolve_impl_trait_item(
 ) -> Option<DocLinkDef> {
     let canonical = ty.canonical();
     let krate = ty.krate(db);
-    let environment = resolver.generic_def().map_or_else(
-        || crate::TraitEnvironment::empty(krate.id).into(),
-        |d| db.trait_environment(d),
-    );
+    let environment = resolver
+        .generic_def()
+        .map_or_else(|| crate::TraitEnvironment::empty(krate.id), |d| db.trait_environment(d));
     let traits_in_scope = resolver.traits_in_scope(db.upcast());
 
     let mut result = None;
@@ -297,7 +296,7 @@ fn as_module_def_if_namespace_matches(
         AssocItem::TypeAlias(it) => (ModuleDef::TypeAlias(it), Namespace::Types),
     };
 
-    (ns.unwrap_or(expected_ns) == expected_ns).then(|| DocLinkDef::ModuleDef(def))
+    (ns.unwrap_or(expected_ns) == expected_ns).then_some(DocLinkDef::ModuleDef(def))
 }
 
 fn modpath_from_str(link: &str) -> Option<ModPath> {
diff --git a/crates/hir/src/lib.rs b/crates/hir/src/lib.rs
index 28decd4ce71..1e21045e981 100644
--- a/crates/hir/src/lib.rs
+++ b/crates/hir/src/lib.rs
@@ -236,7 +236,7 @@ impl Crate {
         query: import_map::Query,
     ) -> impl Iterator<Item = Either<ModuleDef, Macro>> {
         let _p = tracing::span!(tracing::Level::INFO, "query_external_importables");
-        import_map::search_dependencies(db, self.into(), query).into_iter().map(|item| {
+        import_map::search_dependencies(db, self.into(), &query).into_iter().map(|item| {
             match ItemInNs::from(item) {
                 ItemInNs::Types(mod_id) | ItemInNs::Values(mod_id) => Either::Left(mod_id),
                 ItemInNs::Macros(mac_id) => Either::Right(mac_id),
@@ -903,7 +903,7 @@ fn emit_def_diagnostic_(
         }
         DefDiagnosticKind::InvalidDeriveTarget { ast, id } => {
             let node = ast.to_node(db.upcast());
-            let derive = node.attrs().nth(*id as usize);
+            let derive = node.attrs().nth(*id);
             match derive {
                 Some(derive) => {
                     acc.push(
@@ -918,7 +918,7 @@ fn emit_def_diagnostic_(
         }
         DefDiagnosticKind::MalformedDerive { ast, id } => {
             let node = ast.to_node(db.upcast());
-            let derive = node.attrs().nth(*id as usize);
+            let derive = node.attrs().nth(*id);
             match derive {
                 Some(derive) => {
                     acc.push(
diff --git a/crates/ide-assists/src/tests/sourcegen.rs b/crates/ide-assists/src/tests/sourcegen.rs
index ad5ec832875..088d93f9a6b 100644
--- a/crates/ide-assists/src/tests/sourcegen.rs
+++ b/crates/ide-assists/src/tests/sourcegen.rs
@@ -2,6 +2,7 @@
 
 use std::{fmt, fs, path::Path};
 
+use stdx::format_to_acc;
 use test_utils::project_root;
 
 #[test]
@@ -172,8 +173,7 @@ impl fmt::Display for Assist {
 fn hide_hash_comments(text: &str) -> String {
     text.split('\n') // want final newline
         .filter(|&it| !(it.starts_with("# ") || it == "#"))
-        .map(|it| format!("{it}\n"))
-        .collect()
+        .fold(String::new(), |mut acc, it| format_to_acc!(acc, "{it}\n"))
 }
 
 fn reveal_hash_comments(text: &str) -> String {
@@ -187,6 +187,5 @@ fn reveal_hash_comments(text: &str) -> String {
                 it
             }
         })
-        .map(|it| format!("{it}\n"))
-        .collect()
+        .fold(String::new(), |mut acc, it| format_to_acc!(acc, "{it}\n"))
 }
diff --git a/crates/ide-completion/src/context/analysis.rs b/crates/ide-completion/src/context/analysis.rs
index 65ecaf6bac5..c06b64df1c5 100644
--- a/crates/ide-completion/src/context/analysis.rs
+++ b/crates/ide-completion/src/context/analysis.rs
@@ -1267,8 +1267,7 @@ fn pattern_context_for(
     pat
         .syntax()
         .ancestors()
-        .skip_while(|it| ast::Pat::can_cast(it.kind()))
-        .next()
+        .find(|it| !ast::Pat::can_cast(it.kind()))
         .map_or((PatternRefutability::Irrefutable, false), |node| {
             let refutability = match_ast! {
                 match node {
diff --git a/crates/ide-completion/src/tests.rs b/crates/ide-completion/src/tests.rs
index c421be51a0d..154b69875ae 100644
--- a/crates/ide-completion/src/tests.rs
+++ b/crates/ide-completion/src/tests.rs
@@ -210,23 +210,14 @@ pub(crate) fn check_edit_with_config(
 
     let mut combined_edit = completion.text_edit.clone();
 
-    resolve_completion_edits(
-        &db,
-        &config,
-        position,
-        completion
-            .import_to_add
-            .iter()
-            .cloned()
-            .filter_map(|(import_path, import_name)| Some((import_path, import_name))),
-    )
-    .into_iter()
-    .flatten()
-    .for_each(|text_edit| {
-        combined_edit.union(text_edit).expect(
-            "Failed to apply completion resolve changes: change ranges overlap, but should not",
-        )
-    });
+    resolve_completion_edits(&db, &config, position, completion.import_to_add.iter().cloned())
+        .into_iter()
+        .flatten()
+        .for_each(|text_edit| {
+            combined_edit.union(text_edit).expect(
+                "Failed to apply completion resolve changes: change ranges overlap, but should not",
+            )
+        });
 
     combined_edit.apply(&mut actual);
     assert_eq_text!(&ra_fixture_after, &actual)
diff --git a/crates/ide-db/src/imports/merge_imports.rs b/crates/ide-db/src/imports/merge_imports.rs
index 77c32fd852e..b153aafa0e1 100644
--- a/crates/ide-db/src/imports/merge_imports.rs
+++ b/crates/ide-db/src/imports/merge_imports.rs
@@ -467,8 +467,7 @@ fn recursive_normalize(use_tree: &ast::UseTree, style: NormalizationStyle) -> Op
                     }
                     ted::replace_all(start..=end, elements);
                 } else {
-                    let new_use_tree_list =
-                        make::use_tree_list(subtrees.into_iter()).clone_for_update();
+                    let new_use_tree_list = make::use_tree_list(subtrees).clone_for_update();
                     ted::replace(use_tree_list.syntax(), new_use_tree_list.syntax());
                 }
                 modified = true;
diff --git a/crates/ide/src/hover.rs b/crates/ide/src/hover.rs
index 77a06a97e22..19b181ae3b6 100644
--- a/crates/ide/src/hover.rs
+++ b/crates/ide/src/hover.rs
@@ -120,6 +120,7 @@ pub(crate) fn hover(
     Some(res)
 }
 
+#[allow(clippy::field_reassign_with_default)]
 fn hover_simple(
     sema: &Semantics<'_, RootDatabase>,
     FilePosition { file_id, offset }: FilePosition,
diff --git a/crates/proc-macro-api/src/lib.rs b/crates/proc-macro-api/src/lib.rs
index 345608d3d0c..379d184dd68 100644
--- a/crates/proc-macro-api/src/lib.rs
+++ b/crates/proc-macro-api/src/lib.rs
@@ -184,7 +184,7 @@ impl ProcMacro {
             .process
             .lock()
             .unwrap_or_else(|e| e.into_inner())
-            .send_task(msg::Request::ExpandMacro(task))?;
+            .send_task(msg::Request::ExpandMacro(Box::new(task)))?;
 
         match response {
             msg::Response::ExpandMacro(it) => {
diff --git a/crates/proc-macro-api/src/msg.rs b/crates/proc-macro-api/src/msg.rs
index 557ddba5c78..e28fe387b84 100644
--- a/crates/proc-macro-api/src/msg.rs
+++ b/crates/proc-macro-api/src/msg.rs
@@ -29,7 +29,7 @@ pub enum Request {
     /// Since [`NO_VERSION_CHECK_VERSION`]
     ListMacros { dylib_path: PathBuf },
     /// Since [`NO_VERSION_CHECK_VERSION`]
-    ExpandMacro(ExpandMacro),
+    ExpandMacro(Box<ExpandMacro>),
     /// Since [`VERSION_CHECK_VERSION`]
     ApiVersionCheck {},
     /// Since [`RUST_ANALYZER_SPAN_SUPPORT`]
diff --git a/crates/proc-macro-srv-cli/src/main.rs b/crates/proc-macro-srv-cli/src/main.rs
index af9a03826ff..a36200cdb4c 100644
--- a/crates/proc-macro-srv-cli/src/main.rs
+++ b/crates/proc-macro-srv-cli/src/main.rs
@@ -45,9 +45,11 @@ fn run() -> io::Result<()> {
                 msg::Response::ListMacros(srv.list_macros(&dylib_path))
             }
             msg::Request::ExpandMacro(task) => match srv.span_mode() {
-                msg::SpanMode::Id => msg::Response::ExpandMacro(srv.expand(task).map(|(it, _)| it)),
+                msg::SpanMode::Id => {
+                    msg::Response::ExpandMacro(srv.expand(*task).map(|(it, _)| it))
+                }
                 msg::SpanMode::RustAnalyzer => msg::Response::ExpandMacroExtended(
-                    srv.expand(task).map(|(tree, span_data_table)| msg::ExpandMacroExtended {
+                    srv.expand(*task).map(|(tree, span_data_table)| msg::ExpandMacroExtended {
                         tree,
                         span_data_table,
                     }),
diff --git a/crates/project-model/src/workspace.rs b/crates/project-model/src/workspace.rs
index e6e2fa7a978..8c5ea0619ac 100644
--- a/crates/project-model/src/workspace.rs
+++ b/crates/project-model/src/workspace.rs
@@ -60,7 +60,7 @@ pub enum ProjectWorkspace {
         cargo: CargoWorkspace,
         build_scripts: WorkspaceBuildScripts,
         sysroot: Result<Sysroot, Option<String>>,
-        rustc: Result<(CargoWorkspace, WorkspaceBuildScripts), Option<String>>,
+        rustc: Result<Box<(CargoWorkspace, WorkspaceBuildScripts)>, Option<String>>,
         /// Holds cfg flags for the current target. We get those by running
         /// `rustc --print cfg`.
         ///
@@ -119,7 +119,7 @@ impl fmt::Debug for ProjectWorkspace {
                 .field("sysroot", &sysroot.is_ok())
                 .field(
                     "n_rustc_compiler_crates",
-                    &rustc.as_ref().map_or(0, |(rc, _)| rc.packages().len()),
+                    &rustc.as_ref().map(|a| a.as_ref()).map_or(0, |(rc, _)| rc.packages().len()),
                 )
                 .field("n_rustc_cfg", &rustc_cfg.len())
                 .field("n_cfg_overrides", &cfg_overrides.len())
@@ -265,7 +265,7 @@ impl ProjectWorkspace {
                                 cargo_toml.parent(),
                                 &config.extra_env,
                             );
-                            Ok((workspace, buildscripts))
+                            Ok(Box::new((workspace, buildscripts)))
                         }
                         Err(e) => {
                             tracing::error!(
@@ -603,7 +603,7 @@ impl ProjectWorkspace {
                         PackageRoot { is_local, include, exclude }
                     })
                     .chain(mk_sysroot(sysroot.as_ref(), Some(cargo.workspace_root())))
-                    .chain(rustc.iter().flat_map(|(rustc, _)| {
+                    .chain(rustc.iter().map(|a| a.as_ref()).flat_map(|(rustc, _)| {
                         rustc.packages().map(move |krate| PackageRoot {
                             is_local: false,
                             include: vec![rustc[krate].manifest.parent().to_path_buf()],
@@ -631,7 +631,8 @@ impl ProjectWorkspace {
                 sysroot_package_len + project.n_crates()
             }
             ProjectWorkspace::Cargo { cargo, sysroot, rustc, .. } => {
-                let rustc_package_len = rustc.as_ref().map_or(0, |(it, _)| it.packages().len());
+                let rustc_package_len =
+                    rustc.as_ref().map(|a| a.as_ref()).map_or(0, |(it, _)| it.packages().len());
                 let sysroot_package_len = sysroot.as_ref().map_or(0, |it| it.num_packages());
                 cargo.packages().len() + sysroot_package_len + rustc_package_len
             }
@@ -672,7 +673,7 @@ impl ProjectWorkspace {
                 target_layout,
             } => cargo_to_crate_graph(
                 load,
-                rustc.as_ref().ok(),
+                rustc.as_ref().map(|a| a.as_ref()).ok(),
                 cargo,
                 sysroot.as_ref().ok(),
                 rustc_cfg.clone(),
diff --git a/crates/rust-analyzer/src/cli/analysis_stats.rs b/crates/rust-analyzer/src/cli/analysis_stats.rs
index c33fbddceff..31bdd2a0e82 100644
--- a/crates/rust-analyzer/src/cli/analysis_stats.rs
+++ b/crates/rust-analyzer/src/cli/analysis_stats.rs
@@ -58,12 +58,14 @@ impl flags::AnalysisStats {
             Rand32::new(seed)
         };
 
-        let mut cargo_config = CargoConfig::default();
-        cargo_config.sysroot = match self.no_sysroot {
-            true => None,
-            false => Some(RustLibSource::Discover),
+        let cargo_config = CargoConfig {
+            sysroot: match self.no_sysroot {
+                true => None,
+                false => Some(RustLibSource::Discover),
+            },
+            sysroot_query_metadata: self.query_sysroot_metadata,
+            ..Default::default()
         };
-        cargo_config.sysroot_query_metadata = self.query_sysroot_metadata;
         let no_progress = &|_| ();
 
         let mut db_load_sw = self.stop_watch();
diff --git a/crates/rust-analyzer/src/cli/diagnostics.rs b/crates/rust-analyzer/src/cli/diagnostics.rs
index 0182cf5402e..6d2e97be20e 100644
--- a/crates/rust-analyzer/src/cli/diagnostics.rs
+++ b/crates/rust-analyzer/src/cli/diagnostics.rs
@@ -13,8 +13,8 @@ use crate::cli::flags;
 
 impl flags::Diagnostics {
     pub fn run(self) -> anyhow::Result<()> {
-        let mut cargo_config = CargoConfig::default();
-        cargo_config.sysroot = Some(RustLibSource::Discover);
+        let cargo_config =
+            CargoConfig { sysroot: Some(RustLibSource::Discover), ..Default::default() };
         let with_proc_macro_server = if let Some(p) = &self.proc_macro_srv {
             let path = vfs::AbsPathBuf::assert(std::env::current_dir()?.join(p));
             ProcMacroServerChoice::Explicit(path)
diff --git a/crates/rust-analyzer/src/cli/lsif.rs b/crates/rust-analyzer/src/cli/lsif.rs
index 2138ecead53..64f965e22ac 100644
--- a/crates/rust-analyzer/src/cli/lsif.rs
+++ b/crates/rust-analyzer/src/cli/lsif.rs
@@ -287,8 +287,8 @@ impl flags::Lsif {
     pub fn run(self) -> anyhow::Result<()> {
         eprintln!("Generating LSIF started...");
         let now = Instant::now();
-        let mut cargo_config = CargoConfig::default();
-        cargo_config.sysroot = Some(RustLibSource::Discover);
+        let cargo_config =
+            CargoConfig { sysroot: Some(RustLibSource::Discover), ..Default::default() };
         let no_progress = &|_| ();
         let load_cargo_config = LoadCargoConfig {
             load_out_dirs_from_check: true,
diff --git a/crates/rust-analyzer/src/cli/run_tests.rs b/crates/rust-analyzer/src/cli/run_tests.rs
index e1704199151..d07dcdec251 100644
--- a/crates/rust-analyzer/src/cli/run_tests.rs
+++ b/crates/rust-analyzer/src/cli/run_tests.rs
@@ -13,8 +13,8 @@ use crate::cli::{flags, full_name_of_item, Result};
 
 impl flags::RunTests {
     pub fn run(self) -> Result<()> {
-        let mut cargo_config = CargoConfig::default();
-        cargo_config.sysroot = Some(RustLibSource::Discover);
+        let cargo_config =
+            CargoConfig { sysroot: Some(RustLibSource::Discover), ..Default::default() };
         let load_cargo_config = LoadCargoConfig {
             load_out_dirs_from_check: true,
             with_proc_macro_server: ProcMacroServerChoice::Sysroot,
diff --git a/crates/rust-analyzer/src/cli/rustc_tests.rs b/crates/rust-analyzer/src/cli/rustc_tests.rs
index 522eb53128f..be7e434acac 100644
--- a/crates/rust-analyzer/src/cli/rustc_tests.rs
+++ b/crates/rust-analyzer/src/cli/rustc_tests.rs
@@ -59,8 +59,8 @@ impl Tester {
         path.push("ra-rustc-test.rs");
         let tmp_file = AbsPathBuf::try_from(path).unwrap();
         std::fs::write(&tmp_file, "")?;
-        let mut cargo_config = CargoConfig::default();
-        cargo_config.sysroot = Some(RustLibSource::Discover);
+        let cargo_config =
+            CargoConfig { sysroot: Some(RustLibSource::Discover), ..Default::default() };
         let workspace = ProjectWorkspace::DetachedFiles {
             files: vec![tmp_file.clone()],
             sysroot: Ok(Sysroot::discover(
diff --git a/crates/rust-analyzer/src/cli/ssr.rs b/crates/rust-analyzer/src/cli/ssr.rs
index f87dcb889a4..8f11d82f8fd 100644
--- a/crates/rust-analyzer/src/cli/ssr.rs
+++ b/crates/rust-analyzer/src/cli/ssr.rs
@@ -10,8 +10,8 @@ use crate::cli::flags;
 impl flags::Ssr {
     pub fn run(self) -> anyhow::Result<()> {
         use ide_db::base_db::SourceDatabaseExt;
-        let mut cargo_config = CargoConfig::default();
-        cargo_config.sysroot = Some(RustLibSource::Discover);
+        let cargo_config =
+            CargoConfig { sysroot: Some(RustLibSource::Discover), ..Default::default() };
         let load_cargo_config = LoadCargoConfig {
             load_out_dirs_from_check: true,
             with_proc_macro_server: ProcMacroServerChoice::Sysroot,
diff --git a/crates/rust-analyzer/src/config.rs b/crates/rust-analyzer/src/config.rs
index eeb28b8fe42..815f6ea12e8 100644
--- a/crates/rust-analyzer/src/config.rs
+++ b/crates/rust-analyzer/src/config.rs
@@ -32,6 +32,7 @@ use project_model::{
 };
 use rustc_hash::{FxHashMap, FxHashSet};
 use serde::{de::DeserializeOwned, Deserialize};
+use stdx::format_to_acc;
 use vfs::{AbsPath, AbsPathBuf};
 
 use crate::{
@@ -1744,7 +1745,7 @@ impl Config {
     }
 
     pub fn main_loop_num_threads(&self) -> usize {
-        self.data.numThreads.unwrap_or(num_cpus::get_physical().try_into().unwrap_or(1))
+        self.data.numThreads.unwrap_or(num_cpus::get_physical())
     }
 
     pub fn typing_autoclose_angle(&self) -> bool {
@@ -2563,14 +2564,13 @@ fn field_props(field: &str, ty: &str, doc: &[&str], default: &str) -> serde_json
 
 #[cfg(test)]
 fn manual(fields: &[(&'static str, &'static str, &[&str], &str)]) -> String {
-    fields
-        .iter()
-        .map(|(field, _ty, doc, default)| {
-            let name = format!("rust-analyzer.{}", field.replace('_', "."));
-            let doc = doc_comment_to_string(doc);
-            if default.contains('\n') {
-                format!(
-                    r#"[[{name}]]{name}::
+    fields.iter().fold(String::new(), |mut acc, (field, _ty, doc, default)| {
+        let name = format!("rust-analyzer.{}", field.replace('_', "."));
+        let doc = doc_comment_to_string(doc);
+        if default.contains('\n') {
+            format_to_acc!(
+                acc,
+                r#"[[{name}]]{name}::
 +
 --
 Default:
@@ -2580,16 +2580,17 @@ Default:
 {doc}
 --
 "#
-                )
-            } else {
-                format!("[[{name}]]{name} (default: `{default}`)::\n+\n--\n{doc}--\n")
-            }
-        })
-        .collect::<String>()
+            )
+        } else {
+            format_to_acc!(acc, "[[{name}]]{name} (default: `{default}`)::\n+\n--\n{doc}--\n")
+        }
+    })
 }
 
 fn doc_comment_to_string(doc: &[&str]) -> String {
-    doc.iter().map(|it| it.strip_prefix(' ').unwrap_or(it)).map(|it| format!("{it}\n")).collect()
+    doc.iter()
+        .map(|it| it.strip_prefix(' ').unwrap_or(it))
+        .fold(String::new(), |mut acc, it| format_to_acc!(acc, "{it}\n"))
 }
 
 #[cfg(test)]
diff --git a/crates/rust-analyzer/src/lsp/to_proto.rs b/crates/rust-analyzer/src/lsp/to_proto.rs
index f221863aff0..d363ac69fdc 100644
--- a/crates/rust-analyzer/src/lsp/to_proto.rs
+++ b/crates/rust-analyzer/src/lsp/to_proto.rs
@@ -312,16 +312,14 @@ fn completion_item(
     set_score(&mut lsp_item, max_relevance, item.relevance);
 
     if config.completion().enable_imports_on_the_fly && !item.import_to_add.is_empty() {
-        let imports: Vec<_> = item
+        let imports = item
             .import_to_add
             .into_iter()
-            .filter_map(|(import_path, import_name)| {
-                Some(lsp_ext::CompletionImport {
-                    full_import_path: import_path,
-                    imported_name: import_name,
-                })
+            .map(|(import_path, import_name)| lsp_ext::CompletionImport {
+                full_import_path: import_path,
+                imported_name: import_name,
             })
-            .collect();
+            .collect::<Vec<_>>();
         if !imports.is_empty() {
             let data = lsp_ext::CompletionResolveData { position: tdpp.clone(), imports };
             lsp_item.data = Some(to_value(data).unwrap());
diff --git a/crates/rust-analyzer/tests/slow-tests/main.rs b/crates/rust-analyzer/tests/slow-tests/main.rs
index f7f654b890e..19890110d53 100644
--- a/crates/rust-analyzer/tests/slow-tests/main.rs
+++ b/crates/rust-analyzer/tests/slow-tests/main.rs
@@ -31,6 +31,7 @@ use lsp_types::{
 };
 use rust_analyzer::lsp::ext::{OnEnter, Runnables, RunnablesParams};
 use serde_json::json;
+use stdx::format_to_acc;
 use test_utils::skip_slow_tests;
 
 use crate::{
@@ -591,8 +592,10 @@ fn diagnostics_dont_block_typing() {
         return;
     }
 
-    let librs: String = (0..10).map(|i| format!("mod m{i};")).collect();
-    let libs: String = (0..10).map(|i| format!("//- /src/m{i}.rs\nfn foo() {{}}\n\n")).collect();
+    let librs: String = (0..10).fold(String::new(), |mut acc, i| format_to_acc!(acc, "mod m{i};"));
+    let libs: String = (0..10).fold(String::new(), |mut acc, i| {
+        format_to_acc!(acc, "//- /src/m{i}.rs\nfn foo() {{}}\n\n")
+    });
     let server = Project::with_fixture(&format!(
         r#"
 //- /Cargo.toml
diff --git a/crates/stdx/src/macros.rs b/crates/stdx/src/macros.rs
index 8fec7229cf1..85d9008fe12 100644
--- a/crates/stdx/src/macros.rs
+++ b/crates/stdx/src/macros.rs
@@ -14,6 +14,22 @@ macro_rules! format_to {
     };
 }
 
+/// Appends formatted string to a `String` and returns the `String`.
+///
+/// Useful for folding iterators into a `String`.
+#[macro_export]
+macro_rules! format_to_acc {
+    ($buf:expr, $lit:literal $($arg:tt)*) => {
+        {
+            use ::std::fmt::Write as _;
+            // We can't do ::std::fmt::Write::write_fmt($buf, format_args!($lit $($arg)*))
+            // unfortunately, as that loses out on autoref behavior.
+            _ = $buf.write_fmt(format_args!($lit $($arg)*));
+            $buf
+        }
+    };
+}
+
 /// Generates `From` impls for `Enum E { Foo(Foo), Bar(Bar) }` enums
 ///
 /// # Example
diff --git a/crates/syntax/src/ast/make.rs b/crates/syntax/src/ast/make.rs
index 62d64319e38..d5eda8f15e4 100644
--- a/crates/syntax/src/ast/make.rs
+++ b/crates/syntax/src/ast/make.rs
@@ -9,10 +9,11 @@
 //! API should require to assemble every node piecewise. The trick of
 //! `parse(format!())` we use internally is an implementation detail -- long
 //! term, it will be replaced with direct tree manipulation.
+
 use itertools::Itertools;
 use parser::T;
 use rowan::NodeOrToken;
-use stdx::{format_to, never};
+use stdx::{format_to, format_to_acc, never};
 
 use crate::{ast, utils::is_raw_identifier, AstNode, SourceFile, SyntaxKind, SyntaxToken};
 
@@ -759,15 +760,12 @@ pub fn match_arm_with_guard(
 }
 
 pub fn match_arm_list(arms: impl IntoIterator<Item = ast::MatchArm>) -> ast::MatchArmList {
-    let arms_str = arms
-        .into_iter()
-        .map(|arm| {
-            let needs_comma = arm.expr().map_or(true, |it| !it.is_block_like());
-            let comma = if needs_comma { "," } else { "" };
-            let arm = arm.syntax();
-            format!("    {arm}{comma}\n")
-        })
-        .collect::<String>();
+    let arms_str = arms.into_iter().fold(String::new(), |mut acc, arm| {
+        let needs_comma = arm.expr().map_or(true, |it| !it.is_block_like());
+        let comma = if needs_comma { "," } else { "" };
+        let arm = arm.syntax();
+        format_to_acc!(acc, "    {arm}{comma}\n")
+    });
     return from_text(&arms_str);
 
     fn from_text(text: &str) -> ast::MatchArmList {
diff --git a/crates/syntax/src/tests.rs b/crates/syntax/src/tests.rs
index 8ae1242cf7f..4c0a538f712 100644
--- a/crates/syntax/src/tests.rs
+++ b/crates/syntax/src/tests.rs
@@ -11,6 +11,7 @@ use std::{
 use ast::HasName;
 use expect_test::expect_file;
 use rayon::prelude::*;
+use stdx::format_to_acc;
 use test_utils::{bench, bench_fixture, project_root};
 
 use crate::{ast, fuzz, AstNode, SourceFile, SyntaxError};
@@ -104,10 +105,9 @@ fn self_hosting_parsing() {
         .collect::<Vec<_>>();
 
     if !errors.is_empty() {
-        let errors = errors
-            .into_iter()
-            .map(|(path, err)| format!("{}: {:?}\n", path.display(), err[0]))
-            .collect::<String>();
+        let errors = errors.into_iter().fold(String::new(), |mut acc, (path, err)| {
+            format_to_acc!(acc, "{}: {:?}\n", path.display(), err[0])
+        });
         panic!("Parsing errors:\n{errors}\n");
     }
 }