Make collapsible_if recognize the let_chains feature (#14481)

Until `if let` chains are stabilized, we do not collapse them together
or with other `if` expressions unless the `let_chains` feature is
enabled. This is the case for example in Clippy sources.

This was made possible by converting the `collapsible_if` to a late lint
to get access to the set of enabled features. This allows this PR to
supersede #14455 and no longer require an additional configuration
option.

The three commits are, in order:
- a conversion of the existing early lint to a late lint, with no new
feature or tests changes
- the addition of the `let_chains` feature detection and action, and
tests
- the application of the enhanced lint to Clippy sources (136 files
modified)

changelog: [`collapsible_if`]: recognize the rust compiler `let_chains`
feature

r? @flip1995

Author: flip1995

clippy_dev/src/update_lints.rs

@@ -402,53 +402,53 @@ fn remove_lint_declaration(name: &str, path: &Path, lints: &mut Vec<Lint>) -> io
         }
     }
 
-    if path.exists() {
-        if let Some(lint) = lints.iter().find(|l| l.name == name) {
-            if lint.module == name {
-                // The lint name is the same as the file, we can just delete the entire file
-                fs::remove_file(path)?;
-            } else {
-                // We can't delete the entire file, just remove the declaration
-
-                if let Some(Some("mod.rs")) = path.file_name().map(OsStr::to_str) {
-                    // Remove clippy_lints/src/some_mod/some_lint.rs
-                    let mut lint_mod_path = path.to_path_buf();
-                    lint_mod_path.set_file_name(name);
-                    lint_mod_path.set_extension("rs");
+    if path.exists()
+        && let Some(lint) = lints.iter().find(|l| l.name == name)
+    {
+        if lint.module == name {
+            // The lint name is the same as the file, we can just delete the entire file
+            fs::remove_file(path)?;
+        } else {
+            // We can't delete the entire file, just remove the declaration
 
-                    let _ = fs::remove_file(lint_mod_path);
-                }
+            if let Some(Some("mod.rs")) = path.file_name().map(OsStr::to_str) {
+                // Remove clippy_lints/src/some_mod/some_lint.rs
+                let mut lint_mod_path = path.to_path_buf();
+                lint_mod_path.set_file_name(name);
+                lint_mod_path.set_extension("rs");
 
-                let mut content =
-                    fs::read_to_string(path).unwrap_or_else(|_| panic!("failed to read `{}`", path.to_string_lossy()));
+                let _ = fs::remove_file(lint_mod_path);
+            }
 
-                eprintln!(
-                    "warn: you will have to manually remove any code related to `{name}` from `{}`",
-                    path.display()
-                );
+            let mut content =
+                fs::read_to_string(path).unwrap_or_else(|_| panic!("failed to read `{}`", path.to_string_lossy()));
 
-                assert!(
-                    content[lint.declaration_range.clone()].contains(&name.to_uppercase()),
-                    "error: `{}` does not contain lint `{}`'s declaration",
-                    path.display(),
-                    lint.name
-                );
+            eprintln!(
+                "warn: you will have to manually remove any code related to `{name}` from `{}`",
+                path.display()
+            );
 
-                // Remove lint declaration (declare_clippy_lint!)
-                content.replace_range(lint.declaration_range.clone(), "");
+            assert!(
+                content[lint.declaration_range.clone()].contains(&name.to_uppercase()),
+                "error: `{}` does not contain lint `{}`'s declaration",
+                path.display(),
+                lint.name
+            );
 
-                // Remove the module declaration (mod xyz;)
-                let mod_decl = format!("\nmod {name};");
-                content = content.replacen(&mod_decl, "", 1);
+            // Remove lint declaration (declare_clippy_lint!)
+            content.replace_range(lint.declaration_range.clone(), "");
 
-                remove_impl_lint_pass(&lint.name.to_uppercase(), &mut content);
-                fs::write(path, content).unwrap_or_else(|_| panic!("failed to write to `{}`", path.to_string_lossy()));
-            }
+            // Remove the module declaration (mod xyz;)
+            let mod_decl = format!("\nmod {name};");
+            content = content.replacen(&mod_decl, "", 1);
 
-            remove_test_assets(name);
-            remove_lint(name, lints);
-            return Ok(true);
+            remove_impl_lint_pass(&lint.name.to_uppercase(), &mut content);
+            fs::write(path, content).unwrap_or_else(|_| panic!("failed to write to `{}`", path.to_string_lossy()));
         }
+
+        remove_test_assets(name);
+        remove_lint(name, lints);
+        return Ok(true);
     }
 
     Ok(false)

clippy_dev/src/utils.rs

@@ -30,10 +30,10 @@ pub fn clippy_project_root() -> PathBuf {
     let current_dir = std::env::current_dir().unwrap();
     for path in current_dir.ancestors() {
         let result = fs::read_to_string(path.join("Cargo.toml"));
-        if let Err(err) = &result {
-            if err.kind() == io::ErrorKind::NotFound {
-                continue;
-            }
+        if let Err(err) = &result
+            && err.kind() == io::ErrorKind::NotFound
+        {
+            continue;
         }
 
         let content = result.unwrap();

clippy_lints/src/arbitrary_source_item_ordering.rs

@@ -263,10 +263,11 @@ impl<'tcx> LateLintPass<'tcx> for ArbitrarySourceItemOrdering {
                         continue;
                     }
 
-                    if let Some(cur_v) = cur_v {
-                        if cur_v.ident.name.as_str() > variant.ident.name.as_str() && cur_v.span != variant.span {
-                            Self::lint_member_name(cx, &variant.ident, &cur_v.ident);
-                        }
+                    if let Some(cur_v) = cur_v
+                        && cur_v.ident.name.as_str() > variant.ident.name.as_str()
+                        && cur_v.span != variant.span
+                    {
+                        Self::lint_member_name(cx, &variant.ident, &cur_v.ident);
                     }
                     cur_v = Some(variant);
                 }
@@ -278,10 +279,11 @@ impl<'tcx> LateLintPass<'tcx> for ArbitrarySourceItemOrdering {
                         continue;
                     }
 
-                    if let Some(cur_f) = cur_f {
-                        if cur_f.ident.name.as_str() > field.ident.name.as_str() && cur_f.span != field.span {
-                            Self::lint_member_name(cx, &field.ident, &cur_f.ident);
-                        }
+                    if let Some(cur_f) = cur_f
+                        && cur_f.ident.name.as_str() > field.ident.name.as_str()
+                        && cur_f.span != field.span
+                    {
+                        Self::lint_member_name(cx, &field.ident, &cur_f.ident);
                     }
                     cur_f = Some(field);
                 }

clippy_lints/src/attrs/blanket_clippy_restriction_lints.rs

@@ -8,17 +8,18 @@ use rustc_span::{DUMMY_SP, sym};
 
 pub(super) fn check(cx: &EarlyContext<'_>, name: Symbol, items: &[MetaItemInner]) {
     for lint in items {
-        if let Some(lint_name) = extract_clippy_lint(lint) {
-            if lint_name.as_str() == "restriction" && name != sym::allow {
-                span_lint_and_help(
-                    cx,
-                    BLANKET_CLIPPY_RESTRICTION_LINTS,
-                    lint.span(),
-                    "`clippy::restriction` is not meant to be enabled as a group",
-                    None,
-                    "enable the restriction lints you need individually",
-                );
-            }
+        if let Some(lint_name) = extract_clippy_lint(lint)
+            && lint_name.as_str() == "restriction"
+            && name != sym::allow
+        {
+            span_lint_and_help(
+                cx,
+                BLANKET_CLIPPY_RESTRICTION_LINTS,
+                lint.span(),
+                "`clippy::restriction` is not meant to be enabled as a group",
+                None,
+                "enable the restriction lints you need individually",
+            );
         }
     }
 }

clippy_lints/src/attrs/deprecated_semver.rs

@@ -6,10 +6,10 @@ use rustc_span::Span;
 use semver::Version;
 
 pub(super) fn check(cx: &EarlyContext<'_>, span: Span, lit: &MetaItemLit) {
-    if let LitKind::Str(is, _) = lit.kind {
-        if is.as_str() == "TBD" || Version::parse(is.as_str()).is_ok() {
-            return;
-        }
+    if let LitKind::Str(is, _) = lit.kind
+        && (is.as_str() == "TBD" || Version::parse(is.as_str()).is_ok())
+    {
+        return;
     }
     span_lint(
         cx,

clippy_lints/src/attrs/mod.rs

@@ -573,28 +573,27 @@ impl EarlyLintPass for PostExpansionEarlyAttributes {
     }
 
     fn check_attribute(&mut self, cx: &EarlyContext<'_>, attr: &Attribute) {
-        if let Some(items) = &attr.meta_item_list() {
-            if let Some(ident) = attr.ident() {
-                if matches!(ident.name, sym::allow) && self.msrv.meets(msrvs::LINT_REASONS_STABILIZATION) {
-                    allow_attributes::check(cx, attr);
-                }
-                if matches!(ident.name, sym::allow | sym::expect) && self.msrv.meets(msrvs::LINT_REASONS_STABILIZATION)
+        if let Some(items) = &attr.meta_item_list()
+            && let Some(ident) = attr.ident()
+        {
+            if matches!(ident.name, sym::allow) && self.msrv.meets(msrvs::LINT_REASONS_STABILIZATION) {
+                allow_attributes::check(cx, attr);
+            }
+            if matches!(ident.name, sym::allow | sym::expect) && self.msrv.meets(msrvs::LINT_REASONS_STABILIZATION) {
+                allow_attributes_without_reason::check(cx, ident.name, items, attr);
+            }
+            if is_lint_level(ident.name, attr.id) {
+                blanket_clippy_restriction_lints::check(cx, ident.name, items);
+            }
+            if items.is_empty() || !attr.has_name(sym::deprecated) {
+                return;
+            }
+            for item in items {
+                if let MetaItemInner::MetaItem(mi) = &item
+                    && let MetaItemKind::NameValue(lit) = &mi.kind
+                    && mi.has_name(sym::since)
                 {
-                    allow_attributes_without_reason::check(cx, ident.name, items, attr);
-                }
-                if is_lint_level(ident.name, attr.id) {
-                    blanket_clippy_restriction_lints::check(cx, ident.name, items);
-                }
-                if items.is_empty() || !attr.has_name(sym::deprecated) {
-                    return;
-                }
-                for item in items {
-                    if let MetaItemInner::MetaItem(mi) = &item
-                        && let MetaItemKind::NameValue(lit) = &mi.kind
-                        && mi.has_name(sym::since)
-                    {
-                        deprecated_semver::check(cx, item.span(), lit);
-                    }
+                    deprecated_semver::check(cx, item.span(), lit);
                 }
             }
         }

clippy_lints/src/attrs/useless_attribute.rs

@@ -14,75 +14,75 @@ pub(super) fn check(cx: &EarlyContext<'_>, item: &Item, attrs: &[Attribute]) {
         if attr.span.in_external_macro(cx.sess().source_map()) {
             return;
         }
-        if let Some(lint_list) = &attr.meta_item_list() {
-            if attr.ident().is_some_and(|ident| is_lint_level(ident.name, attr.id)) {
-                for lint in lint_list {
-                    match item.kind {
-                        ItemKind::Use(..) => {
-                            let (namespace @ (Some(sym::clippy) | None), Some(name)) = namespace_and_lint(lint) else {
-                                return;
-                            };
+        if let Some(lint_list) = &attr.meta_item_list()
+            && attr.ident().is_some_and(|ident| is_lint_level(ident.name, attr.id))
+        {
+            for lint in lint_list {
+                match item.kind {
+                    ItemKind::Use(..) => {
+                        let (namespace @ (Some(sym::clippy) | None), Some(name)) = namespace_and_lint(lint) else {
+                            return;
+                        };
 
-                            if namespace.is_none()
-                                && matches!(
-                                    name.as_str(),
-                                    "ambiguous_glob_reexports"
-                                        | "dead_code"
-                                        | "deprecated"
-                                        | "hidden_glob_reexports"
-                                        | "unreachable_pub"
-                                        | "unused"
-                                        | "unused_braces"
-                                        | "unused_import_braces"
-                                        | "unused_imports"
-                                )
-                            {
-                                return;
-                            }
+                        if namespace.is_none()
+                            && matches!(
+                                name.as_str(),
+                                "ambiguous_glob_reexports"
+                                    | "dead_code"
+                                    | "deprecated"
+                                    | "hidden_glob_reexports"
+                                    | "unreachable_pub"
+                                    | "unused"
+                                    | "unused_braces"
+                                    | "unused_import_braces"
+                                    | "unused_imports"
+                            )
+                        {
+                            return;
+                        }
 
-                            if namespace == Some(sym::clippy)
-                                && matches!(
-                                    name.as_str(),
-                                    "wildcard_imports"
-                                        | "enum_glob_use"
-                                        | "redundant_pub_crate"
-                                        | "macro_use_imports"
-                                        | "unsafe_removed_from_name"
-                                        | "module_name_repetitions"
-                                        | "single_component_path_imports"
-                                        | "disallowed_types"
-                                        | "unused_trait_names"
-                                )
-                            {
-                                return;
-                            }
-                        },
-                        ItemKind::ExternCrate(..) => {
-                            if is_word(lint, sym::unused_imports) && skip_unused_imports {
-                                return;
-                            }
-                            if is_word(lint, sym!(unused_extern_crates)) {
-                                return;
-                            }
-                        },
-                        _ => {},
-                    }
+                        if namespace == Some(sym::clippy)
+                            && matches!(
+                                name.as_str(),
+                                "wildcard_imports"
+                                    | "enum_glob_use"
+                                    | "redundant_pub_crate"
+                                    | "macro_use_imports"
+                                    | "unsafe_removed_from_name"
+                                    | "module_name_repetitions"
+                                    | "single_component_path_imports"
+                                    | "disallowed_types"
+                                    | "unused_trait_names"
+                            )
+                        {
+                            return;
+                        }
+                    },
+                    ItemKind::ExternCrate(..) => {
+                        if is_word(lint, sym::unused_imports) && skip_unused_imports {
+                            return;
+                        }
+                        if is_word(lint, sym!(unused_extern_crates)) {
+                            return;
+                        }
+                    },
+                    _ => {},
                 }
-                let line_span = first_line_of_span(cx, attr.span);
+            }
+            let line_span = first_line_of_span(cx, attr.span);
 
-                if let Some(src) = line_span.get_source_text(cx) {
-                    if src.contains("#[") {
-                        #[expect(clippy::collapsible_span_lint_calls)]
-                        span_lint_and_then(cx, USELESS_ATTRIBUTE, line_span, "useless lint attribute", |diag| {
-                            diag.span_suggestion(
-                                line_span,
-                                "if you just forgot a `!`, use",
-                                src.replacen("#[", "#![", 1),
-                                Applicability::MaybeIncorrect,
-                            );
-                        });
-                    }
-                }
+            if let Some(src) = line_span.get_source_text(cx)
+                && src.contains("#[")
+            {
+                #[expect(clippy::collapsible_span_lint_calls)]
+                span_lint_and_then(cx, USELESS_ATTRIBUTE, line_span, "useless lint attribute", |diag| {
+                    diag.span_suggestion(
+                        line_span,
+                        "if you just forgot a `!`, use",
+                        src.replacen("#[", "#![", 1),
+                        Applicability::MaybeIncorrect,
+                    );
+                });
             }
         }
     }

clippy_lints/src/await_holding_invalid.rs

@@ -192,10 +192,9 @@ impl<'tcx> LateLintPass<'tcx> for AwaitHolding {
             def_id,
             ..
         }) = expr.kind
+            && let Some(coroutine_layout) = cx.tcx.mir_coroutine_witnesses(*def_id)
         {
-            if let Some(coroutine_layout) = cx.tcx.mir_coroutine_witnesses(*def_id) {
-                self.check_interior_types(cx, coroutine_layout);
-            }
+            self.check_interior_types(cx, coroutine_layout);
         }
     }
 }