Auto merge of #9279 - tabokie:weight-loss, r=flip1995

chore: a few small improvements to code quality

Some improvements:
- Simplify implementation of `is_unit_type`
- Use slice matching to destruct `Call` or `MethodCall` whenever possible

changelog: none

r? `@flip1995`

clippy_lints/src/checked_conversions.rs

@@ -270,10 +270,7 @@ fn get_types_from_cast<'a>(
     let limit_from: Option<(&Expr<'_>, &str)> = call_from_cast.or_else(|| {
         if_chain! {
             // `from_type::from, to_type::max_value()`
-            if let ExprKind::Call(from_func, args) = &expr.kind;
-            // `to_type::max_value()`
-            if args.len() == 1;
-            if let limit = &args[0];
+            if let ExprKind::Call(from_func, [limit]) = &expr.kind;
             // `from_type::from`
             if let ExprKind::Path(ref path) = &from_func.kind;
             if let Some(from_sym) = get_implementing_type(path, INTS, "from");

clippy_lints/src/create_dir.rs

@@ -34,7 +34,7 @@ declare_lint_pass!(CreateDir => [CREATE_DIR]);
 impl LateLintPass<'_> for CreateDir {
     fn check_expr(&mut self, cx: &LateContext<'_>, expr: &Expr<'_>) {
         if_chain! {
-            if let ExprKind::Call(func, args) = expr.kind;
+            if let ExprKind::Call(func, [arg, ..]) = expr.kind;
             if let ExprKind::Path(ref path) = func.kind;
             if let Some(def_id) = cx.qpath_res(path, func.hir_id).opt_def_id();
             if match_def_path(cx, def_id, &paths::STD_FS_CREATE_DIR);
@@ -45,7 +45,7 @@ impl LateLintPass<'_> for CreateDir {
                     expr.span,
                     "calling `std::fs::create_dir` where there may be a better way",
                     "consider calling `std::fs::create_dir_all` instead",
-                    format!("create_dir_all({})", snippet(cx, args[0].span, "..")),
+                    format!("create_dir_all({})", snippet(cx, arg.span, "..")),
                     Applicability::MaybeIncorrect,
                 )
             }

clippy_lints/src/from_str_radix_10.rs

@@ -46,7 +46,7 @@ declare_lint_pass!(FromStrRadix10 => [FROM_STR_RADIX_10]);
 impl<'tcx> LateLintPass<'tcx> for FromStrRadix10 {
     fn check_expr(&mut self, cx: &LateContext<'tcx>, exp: &Expr<'tcx>) {
         if_chain! {
-            if let ExprKind::Call(maybe_path, arguments) = &exp.kind;
+            if let ExprKind::Call(maybe_path, [src, radix]) = &exp.kind;
             if let ExprKind::Path(QPath::TypeRelative(ty, pathseg)) = &maybe_path.kind;
 
             // check if the first part of the path is some integer primitive
@@ -60,20 +60,19 @@ impl<'tcx> LateLintPass<'tcx> for FromStrRadix10 {
             if pathseg.ident.name.as_str() == "from_str_radix";
 
             // check if the second argument is a primitive `10`
-            if arguments.len() == 2;
-            if let ExprKind::Lit(lit) = &arguments[1].kind;
+            if let ExprKind::Lit(lit) = &radix.kind;
             if let rustc_ast::ast::LitKind::Int(10, _) = lit.node;
 
             then {
-                let expr = if let ExprKind::AddrOf(_, _, expr) = &arguments[0].kind {
+                let expr = if let ExprKind::AddrOf(_, _, expr) = &src.kind {
                     let ty = cx.typeck_results().expr_ty(expr);
                     if is_ty_stringish(cx, ty) {
                         expr
                     } else {
-                        &arguments[0]
+                        &src
                     }
                 } else {
-                    &arguments[0]
+                    &src
                 };
 
                 let sugg = Sugg::hir_with_applicability(

clippy_lints/src/loops/manual_memcpy.rs

@@ -119,11 +119,9 @@ fn build_manual_memcpy_suggestion<'tcx>(
 
     let print_limit = |end: &Expr<'_>, end_str: &str, base: &Expr<'_>, sugg: MinifyingSugg<'static>| {
         if_chain! {
-            if let ExprKind::MethodCall(method, len_args, _) = end.kind;
+            if let ExprKind::MethodCall(method, [recv], _) = end.kind;
             if method.ident.name == sym::len;
-            if len_args.len() == 1;
-            if let Some(arg) = len_args.get(0);
-            if path_to_local(arg) == path_to_local(base);
+            if path_to_local(recv) == path_to_local(base);
             then {
                 if sugg.to_string() == end_str {
                     sugg::EMPTY.into()
@@ -343,10 +341,8 @@ fn get_slice_like_element_ty<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>) -> Opti
 
 fn fetch_cloned_expr<'tcx>(expr: &'tcx Expr<'tcx>) -> &'tcx Expr<'tcx> {
     if_chain! {
-        if let ExprKind::MethodCall(method, args, _) = expr.kind;
+        if let ExprKind::MethodCall(method, [arg], _) = expr.kind;
         if method.ident.name == sym::clone;
-        if args.len() == 1;
-        if let Some(arg) = args.get(0);
         then { arg } else { expr }
     }
 }

clippy_lints/src/loops/needless_range_loop.rs

@@ -188,10 +188,9 @@ pub(super) fn check<'tcx>(
 
 fn is_len_call(expr: &Expr<'_>, var: Symbol) -> bool {
     if_chain! {
-        if let ExprKind::MethodCall(method, len_args, _) = expr.kind;
-        if len_args.len() == 1;
+        if let ExprKind::MethodCall(method, [recv], _) = expr.kind;
         if method.ident.name == sym::len;
-        if let ExprKind::Path(QPath::Resolved(_, path)) = len_args[0].kind;
+        if let ExprKind::Path(QPath::Resolved(_, path)) = recv.kind;
         if path.segments.len() == 1;
         if path.segments[0].ident.name == var;
         then {

clippy_lints/src/manual_ok_or.rs

@@ -47,17 +47,14 @@ impl<'tcx> LateLintPass<'tcx> for ManualOkOr {
         }
 
         if_chain! {
-            if let ExprKind::MethodCall(method_segment, args, _) = scrutinee.kind;
+            if let ExprKind::MethodCall(method_segment, [receiver, or_expr, map_expr], _) = scrutinee.kind;
             if method_segment.ident.name == sym!(map_or);
-            if args.len() == 3;
-            let method_receiver = &args[0];
-            let ty = cx.typeck_results().expr_ty(method_receiver);
+            let ty = cx.typeck_results().expr_ty(receiver);
             if is_type_diagnostic_item(cx, ty, sym::Option);
-            let or_expr = &args[1];
-            if is_ok_wrapping(cx, &args[2]);
+            if is_ok_wrapping(cx, map_expr);
             if let ExprKind::Call(Expr { kind: ExprKind::Path(err_path), .. }, &[ref err_arg]) = or_expr.kind;
             if is_lang_ctor(cx, err_path, ResultErr);
-            if let Some(method_receiver_snippet) = snippet_opt(cx, method_receiver.span);
+            if let Some(method_receiver_snippet) = snippet_opt(cx, receiver.span);
             if let Some(err_arg_snippet) = snippet_opt(cx, err_arg.span);
             if let Some(indent) = indent_of(cx, scrutinee.span);
             then {

clippy_lints/src/map_err_ignore.rs

@@ -113,18 +113,18 @@ impl<'tcx> LateLintPass<'tcx> for MapErrIgnore {
         }
 
         // check if this is a method call (e.g. x.foo())
-        if let ExprKind::MethodCall(method, args, _) = e.kind {
+        if let ExprKind::MethodCall(method, [_, arg], _) = e.kind {
             // only work if the method name is `map_err` and there are only 2 arguments (e.g. x.map_err(|_|[1]
             // Enum::Variant[2]))
-            if method.ident.as_str() == "map_err" && args.len() == 2 {
+            if method.ident.name == sym!(map_err) {
                 // make sure the first argument is a closure, and grab the CaptureRef, BodyId, and fn_decl_span
                 // fields
                 if let ExprKind::Closure(&Closure {
                     capture_clause,
                     body,
                     fn_decl_span,
                     ..
-                }) = args[1].kind
+                }) = arg.kind
                 {
                     // check if this is by Reference (meaning there's no move statement)
                     if capture_clause == CaptureBy::Ref {

clippy_lints/src/map_unit_fn.rs

@@ -97,11 +97,7 @@ declare_clippy_lint! {
 declare_lint_pass!(MapUnit => [OPTION_MAP_UNIT_FN, RESULT_MAP_UNIT_FN]);
 
 fn is_unit_type(ty: Ty<'_>) -> bool {
-    match ty.kind() {
-        ty::Tuple(slice) => slice.is_empty(),
-        ty::Never => true,
-        _ => false,
-    }
+    ty.is_unit() || ty.is_never()
 }
 
 fn is_unit_function(cx: &LateContext<'_>, expr: &hir::Expr<'_>) -> bool {

clippy_lints/src/matches/match_as_ref.rs

@@ -72,10 +72,10 @@ fn is_ref_some_arm(cx: &LateContext<'_>, arm: &Arm<'_>) -> Option<BindingAnnotat
         if is_lang_ctor(cx, qpath, LangItem::OptionSome);
         if let PatKind::Binding(rb, .., ident, _) = first_pat.kind;
         if rb == BindingAnnotation::Ref || rb == BindingAnnotation::RefMut;
-        if let ExprKind::Call(e, args) = peel_blocks(arm.body).kind;
+        if let ExprKind::Call(e, [arg]) = peel_blocks(arm.body).kind;
         if let ExprKind::Path(ref some_path) = e.kind;
-        if is_lang_ctor(cx, some_path, LangItem::OptionSome) && args.len() == 1;
-        if let ExprKind::Path(QPath::Resolved(_, path2)) = args[0].kind;
+        if is_lang_ctor(cx, some_path, LangItem::OptionSome);
+        if let ExprKind::Path(QPath::Resolved(_, path2)) = arg.kind;
         if path2.segments.len() == 1 && ident.name == path2.segments[0].ident.name;
         then {
             return Some(rb)

clippy_lints/src/matches/try_err.rs

@@ -23,12 +23,10 @@ pub(super) fn check<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>, scrutine
     //         val,
     // };
     if_chain! {
-        if let ExprKind::Call(match_fun, try_args) = scrutinee.kind;
+        if let ExprKind::Call(match_fun, [try_arg, ..]) = scrutinee.kind;
         if let ExprKind::Path(ref match_fun_path) = match_fun.kind;
         if matches!(match_fun_path, QPath::LangItem(LangItem::TryTraitBranch, ..));
-        if let Some(try_arg) = try_args.get(0);
-        if let ExprKind::Call(err_fun, err_args) = try_arg.kind;
-        if let Some(err_arg) = err_args.get(0);
+        if let ExprKind::Call(err_fun, [err_arg, ..]) = try_arg.kind;
         if let ExprKind::Path(ref err_fun_path) = err_fun.kind;
         if is_lang_ctor(cx, err_fun_path, ResultErr);
         if let Some(return_ty) = find_return_type(cx, &expr.kind);

clippy_lints/src/mem_replace.rs

@@ -163,8 +163,7 @@ fn check_replace_with_uninit(cx: &LateContext<'_>, src: &Expr<'_>, dest: &Expr<'
     }
 
     if_chain! {
-        if let ExprKind::Call(repl_func, repl_args) = src.kind;
-        if repl_args.is_empty();
+        if let ExprKind::Call(repl_func, []) = src.kind;
         if let ExprKind::Path(ref repl_func_qpath) = repl_func.kind;
         if let Some(repl_def_id) = cx.qpath_res(repl_func_qpath, repl_func.hir_id).opt_def_id();
         then {
@@ -246,11 +245,10 @@ impl<'tcx> LateLintPass<'tcx> for MemReplace {
     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
         if_chain! {
             // Check that `expr` is a call to `mem::replace()`
-            if let ExprKind::Call(func, func_args) = expr.kind;
+            if let ExprKind::Call(func, [dest, src]) = expr.kind;
             if let ExprKind::Path(ref func_qpath) = func.kind;
             if let Some(def_id) = cx.qpath_res(func_qpath, func.hir_id).opt_def_id();
             if cx.tcx.is_diagnostic_item(sym::mem_replace, def_id);
-            if let [dest, src] = func_args;
             then {
                 check_replace_option_with_none(cx, src, dest, expr.span);
                 check_replace_with_uninit(cx, src, dest, expr.span);

clippy_lints/src/path_buf_push_overwrite.rs

@@ -46,11 +46,9 @@ declare_lint_pass!(PathBufPushOverwrite => [PATH_BUF_PUSH_OVERWRITE]);
 impl<'tcx> LateLintPass<'tcx> for PathBufPushOverwrite {
     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
         if_chain! {
-            if let ExprKind::MethodCall(path, args, _) = expr.kind;
+            if let ExprKind::MethodCall(path, [recv, get_index_arg], _) = expr.kind;
             if path.ident.name == sym!(push);
-            if args.len() == 2;
-            if is_type_diagnostic_item(cx, cx.typeck_results().expr_ty(&args[0]).peel_refs(), sym::PathBuf);
-            if let Some(get_index_arg) = args.get(1);
+            if is_type_diagnostic_item(cx, cx.typeck_results().expr_ty(recv).peel_refs(), sym::PathBuf);
             if let ExprKind::Lit(ref lit) = get_index_arg.kind;
             if let LitKind::Str(ref path_lit, _) = lit.node;
             if let pushed_path = Path::new(path_lit.as_str());

clippy_lints/src/question_mark.rs

@@ -86,8 +86,7 @@ fn check_is_none_or_err_and_early_return<'tcx>(cx: &LateContext<'tcx>, expr: &Ex
     if_chain! {
         if let Some(higher::If { cond, then, r#else }) = higher::If::hir(expr);
         if !is_else_clause(cx.tcx, expr);
-        if let ExprKind::MethodCall(segment, args, _) = &cond.kind;
-        if let Some(caller) = args.get(0);
+        if let ExprKind::MethodCall(segment, [caller, ..], _) = &cond.kind;
         let caller_ty = cx.typeck_results().expr_ty(caller);
         let if_block = IfBlockType::IfIs(caller, caller_ty, segment.ident.name, then, r#else);
         if is_early_return(sym::Option, cx, &if_block) || is_early_return(sym::Result, cx, &if_block);

clippy_lints/src/ranges.rs

@@ -385,24 +385,24 @@ fn check_range_zip_with_len(cx: &LateContext<'_>, path: &PathSegment<'_>, args:
         if path.ident.as_str() == "zip";
         if let [iter, zip_arg] = args;
         // `.iter()` call
-        if let ExprKind::MethodCall(iter_path, iter_args, _) = iter.kind;
+        if let ExprKind::MethodCall(iter_path, [iter_caller, ..], _) = iter.kind;
         if iter_path.ident.name == sym::iter;
         // range expression in `.zip()` call: `0..x.len()`
         if let Some(higher::Range { start: Some(start), end: Some(end), .. }) = higher::Range::hir(zip_arg);
         if is_integer_const(cx, start, 0);
         // `.len()` call
-        if let ExprKind::MethodCall(len_path, len_args, _) = end.kind;
-        if len_path.ident.name == sym::len && len_args.len() == 1;
+        if let ExprKind::MethodCall(len_path, [len_caller], _) = end.kind;
+        if len_path.ident.name == sym::len;
         // `.iter()` and `.len()` called on same `Path`
-        if let ExprKind::Path(QPath::Resolved(_, iter_path)) = iter_args[0].kind;
-        if let ExprKind::Path(QPath::Resolved(_, len_path)) = len_args[0].kind;
+        if let ExprKind::Path(QPath::Resolved(_, iter_path)) = iter_caller.kind;
+        if let ExprKind::Path(QPath::Resolved(_, len_path)) = len_caller.kind;
         if SpanlessEq::new(cx).eq_path_segments(iter_path.segments, len_path.segments);
         then {
             span_lint(cx,
                 RANGE_ZIP_WITH_LEN,
                 span,
                 &format!("it is more idiomatic to use `{}.iter().enumerate()`",
-                    snippet(cx, iter_args[0].span, "_"))
+                    snippet(cx, iter_caller.span, "_"))
             );
         }
     }

clippy_lints/src/regex.rs

@@ -57,21 +57,20 @@ declare_lint_pass!(Regex => [INVALID_REGEX, TRIVIAL_REGEX]);
 impl<'tcx> LateLintPass<'tcx> for Regex {
     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
         if_chain! {
-            if let ExprKind::Call(fun, args) = expr.kind;
+            if let ExprKind::Call(fun, [arg]) = expr.kind;
             if let ExprKind::Path(ref qpath) = fun.kind;
-            if args.len() == 1;
             if let Some(def_id) = cx.qpath_res(qpath, fun.hir_id).opt_def_id();
             then {
                 if match_def_path(cx, def_id, &paths::REGEX_NEW) ||
                    match_def_path(cx, def_id, &paths::REGEX_BUILDER_NEW) {
-                    check_regex(cx, &args[0], true);
+                    check_regex(cx, arg, true);
                 } else if match_def_path(cx, def_id, &paths::REGEX_BYTES_NEW) ||
                    match_def_path(cx, def_id, &paths::REGEX_BYTES_BUILDER_NEW) {
-                    check_regex(cx, &args[0], false);
+                    check_regex(cx, arg, false);
                 } else if match_def_path(cx, def_id, &paths::REGEX_SET_NEW) {
-                    check_set(cx, &args[0], true);
+                    check_set(cx, arg, true);
                 } else if match_def_path(cx, def_id, &paths::REGEX_BYTES_SET_NEW) {
-                    check_set(cx, &args[0], false);
+                    check_set(cx, arg, false);
                 }
             }
         }

clippy_lints/src/slow_vector_initialization.rs

@@ -233,15 +233,10 @@ impl<'a, 'tcx> VectorInitializationVisitor<'a, 'tcx> {
     /// Returns `true` if give expression is `repeat(0).take(...)`
     fn is_repeat_take(&self, expr: &Expr<'_>) -> bool {
         if_chain! {
-            if let ExprKind::MethodCall(take_path, take_args, _) = expr.kind;
+            if let ExprKind::MethodCall(take_path, [recv, len_arg, ..], _) = expr.kind;
             if take_path.ident.name == sym!(take);
-
             // Check that take is applied to `repeat(0)`
-            if let Some(repeat_expr) = take_args.get(0);
-            if self.is_repeat_zero(repeat_expr);
-
-            if let Some(len_arg) = take_args.get(1);
-
+            if self.is_repeat_zero(recv);
             then {
                 // Check that len expression is equals to `with_capacity` expression
                 if SpanlessEq::new(self.cx).eq_expr(len_arg, self.vec_alloc.len_expr) {

clippy_lints/src/stable_sort_primitive.rs

@@ -97,12 +97,11 @@ struct LintDetection {
 
 fn detect_stable_sort_primitive(cx: &LateContext<'_>, expr: &Expr<'_>) -> Option<LintDetection> {
     if_chain! {
-        if let ExprKind::MethodCall(method_name, args, _) = &expr.kind;
-        if let Some(slice) = &args.get(0);
+        if let ExprKind::MethodCall(method_name, [slice, args @ ..], _) = &expr.kind;
         if let Some(method) = SortingKind::from_stable_name(method_name.ident.name.as_str());
         if let Some(slice_type) = is_slice_of_primitives(cx, slice);
         then {
-            let args_str = args.iter().skip(1).map(|arg| Sugg::hir(cx, arg, "..").to_string()).collect::<Vec<String>>().join(", ");
+            let args_str = args.iter().map(|arg| Sugg::hir(cx, arg, "..").to_string()).collect::<Vec<String>>().join(", ");
             Some(LintDetection { slice_name: Sugg::hir(cx, slice, "..").to_string(), method, method_args: args_str, slice_type })
         } else {
             None