[get_first]: lint on non-primitive slices

clippy_lints/src/loops/same_item_push.rs

@@ -185,7 +185,7 @@ fn get_vec_push<'tcx>(
             if let StmtKind::Semi(semi_stmt) = &stmt.kind;
             if let ExprKind::MethodCall(path, self_expr, args, _) = &semi_stmt.kind;
             // Figure out the parameters for the method call
-            if let Some(pushed_item) = args.get(0);
+            if let Some(pushed_item) = args.first();
             // Check that the method being called is push() on a Vec
             if is_type_diagnostic_item(cx, cx.typeck_results().expr_ty(self_expr), sym::Vec);
             if path.ident.name.as_str() == "push";

clippy_lints/src/manual_bits.rs

@@ -103,9 +103,9 @@ fn get_size_of_ty<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) -> Option<
         if let ExprKind::Path(ref count_func_qpath) = count_func.kind;
 
         if let QPath::Resolved(_, count_func_path) = count_func_qpath;
-        if let Some(segment_zero) = count_func_path.segments.get(0);
+        if let Some(segment_zero) = count_func_path.segments.first();
         if let Some(args) = segment_zero.args;
-        if let Some(GenericArg::Type(real_ty)) = args.args.get(0);
+        if let Some(GenericArg::Type(real_ty)) = args.args.first();
 
         if let Some(def_id) = cx.qpath_res(count_func_qpath, count_func.hir_id).opt_def_id();
         if cx.tcx.is_diagnostic_item(sym::mem_size_of, def_id);

clippy_lints/src/methods/get_first.rs

@@ -1,5 +1,4 @@
 use clippy_utils::diagnostics::span_lint_and_sugg;
-use clippy_utils::is_slice_of_primitives;
 use clippy_utils::source::snippet_with_applicability;
 use if_chain::if_chain;
 use rustc_ast::LitKind;
@@ -20,7 +19,6 @@ pub(super) fn check<'tcx>(
         if let Some(method_id) = cx.typeck_results().type_dependent_def_id(expr.hir_id);
         if let Some(impl_id) = cx.tcx.impl_of_method(method_id);
         if cx.tcx.type_of(impl_id).instantiate_identity().is_slice();
-        if let Some(_) = is_slice_of_primitives(cx, recv);
         if let hir::ExprKind::Lit(Spanned { node: LitKind::Int(0, _), .. }) = arg.kind;
         then {
             let mut app = Applicability::MachineApplicable;

clippy_lints/src/methods/search_is_some.rs

@@ -39,7 +39,7 @@ pub(super) fn check<'tcx>(
                 if search_method == "find";
                 if let hir::ExprKind::Closure(&hir::Closure { body, .. }) = search_arg.kind;
                 let closure_body = cx.tcx.hir().body(body);
-                if let Some(closure_arg) = closure_body.params.get(0);
+                if let Some(closure_arg) = closure_body.params.first();
                 then {
                     if let hir::PatKind::Ref(..) = closure_arg.pat.kind {
                         Some(search_snippet.replacen('&', "", 1))

clippy_lints/src/missing_doc.rs

@@ -67,7 +67,7 @@ impl MissingDoc {
         if_chain! {
             if let Some(meta) = meta;
             if let MetaItemKind::List(list) = meta.kind;
-            if let Some(meta) = list.get(0);
+            if let Some(meta) = list.first();
             if let Some(name) = meta.ident();
             then {
                 name.name == sym::include

clippy_lints/src/needless_continue.rs

@@ -189,7 +189,7 @@ fn needless_continue_in_else(else_expr: &ast::Expr, label: Option<&ast::Label>)
 }
 
 fn is_first_block_stmt_continue(block: &ast::Block, label: Option<&ast::Label>) -> bool {
-    block.stmts.get(0).map_or(false, |stmt| match stmt.kind {
+    block.stmts.first().map_or(false, |stmt| match stmt.kind {
         ast::StmtKind::Semi(ref e) | ast::StmtKind::Expr(ref e) => {
             if let ast::ExprKind::Continue(ref l) = e.kind {
                 compare_labels(label, l.as_ref())
@@ -434,7 +434,7 @@ fn erode_from_back(s: &str) -> String {
 }
 
 fn span_of_first_expr_in_block(block: &ast::Block) -> Option<Span> {
-    block.stmts.get(0).map(|stmt| stmt.span)
+    block.stmts.first().map(|stmt| stmt.span)
 }
 
 #[cfg(test)]

clippy_lints/src/slow_vector_initialization.rs

@@ -335,7 +335,7 @@ impl<'a, 'tcx> Visitor<'tcx> for VectorInitializationVisitor<'a, 'tcx> {
 
     fn visit_block(&mut self, block: &'tcx Block<'_>) {
         if self.initialization_found {
-            if let Some(s) = block.stmts.get(0) {
+            if let Some(s) = block.stmts.first() {
                 self.visit_stmt(s);
             }
 

clippy_lints/src/uninit_vec.rs

@@ -201,7 +201,7 @@ fn extract_set_len_self<'tcx>(cx: &LateContext<'_>, expr: &'tcx Expr<'_>) -> Opt
     let expr = peel_hir_expr_while(expr, |e| {
         if let ExprKind::Block(block, _) = e.kind {
             // Extract the first statement/expression
-            match (block.stmts.get(0).map(|stmt| &stmt.kind), block.expr) {
+            match (block.stmts.first().map(|stmt| &stmt.kind), block.expr) {
                 (None, Some(expr)) => Some(expr),
                 (Some(StmtKind::Expr(expr) | StmtKind::Semi(expr)), _) => Some(expr),
                 _ => None,

clippy_lints/src/unnecessary_map_on_constructor.rs

@@ -40,7 +40,7 @@ impl<'tcx> LateLintPass<'tcx> for UnnecessaryMapOnConstructor {
             let (constructor_path, constructor_item) =
                 if let hir::ExprKind::Call(constructor, constructor_args) = recv.kind
                     && let hir::ExprKind::Path(constructor_path) = constructor.kind
-                    && let Some(arg) = constructor_args.get(0)
+                    && let Some(arg) = constructor_args.first()
                 {
                     if constructor.span.from_expansion() || arg.span.from_expansion() {
                         return;
@@ -66,7 +66,7 @@ impl<'tcx> LateLintPass<'tcx> for UnnecessaryMapOnConstructor {
                 _ => return,
             }
 
-            if let Some(map_arg) = args.get(0)
+            if let Some(map_arg) = args.first()
                 && let hir::ExprKind::Path(fun) = map_arg.kind
             {
                 if map_arg.span.from_expansion() {

clippy_utils/src/consts.rs

@@ -504,7 +504,7 @@ impl<'a, 'tcx> ConstEvalLateContext<'a, 'tcx> {
             },
             (Some(Constant::Vec(vec)), _) => {
                 if !vec.is_empty() && vec.iter().all(|x| *x == vec[0]) {
-                    match vec.get(0) {
+                    match vec.first() {
                         Some(Constant::F32(x)) => Some(Constant::F32(*x)),
                         Some(Constant::F64(x)) => Some(Constant::F64(*x)),
                         _ => None,

clippy_utils/src/higher.rs

@@ -449,7 +449,7 @@ pub fn get_vec_init_kind<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) -
                 } else if name.ident.name == symbol::kw::Default {
                     return Some(VecInitKind::Default);
                 } else if name.ident.name.as_str() == "with_capacity" {
-                    let arg = args.get(0)?;
+                    let arg = args.first()?;
                     return match constant_simple(cx, cx.typeck_results(), arg) {
                         Some(Constant::Int(num)) => Some(VecInitKind::WithConstCapacity(num)),
                         _ => Some(VecInitKind::WithExprCapacity(arg.hir_id)),

tests/ui/get_first.fixed

@@ -14,17 +14,20 @@ impl Bar {
 
 fn main() {
     let x = vec![2, 3, 5];
-    let _ = x.first(); // Use x.first()
+    let _ = x.first();
+    //~^ ERROR: accessing first element with `x.get(0)`
     let _ = x.get(1);
     let _ = x[0];
 
     let y = [2, 3, 5];
-    let _ = y.first(); // Use y.first()
+    let _ = y.first();
+    //~^ ERROR: accessing first element with `y.get(0)`
     let _ = y.get(1);
     let _ = y[0];
 
     let z = &[2, 3, 5];
-    let _ = z.first(); // Use z.first()
+    let _ = z.first();
+    //~^ ERROR: accessing first element with `z.get(0)`
     let _ = z.get(1);
     let _ = z[0];
 
@@ -37,4 +40,8 @@ fn main() {
 
     let bar = Bar { arr: [0, 1, 2] };
     let _ = bar.get(0); // Do not lint, because Bar is struct.
+
+    let non_primitives = [vec![1, 2], vec![3, 4]];
+    let _ = non_primitives.first();
+    //~^ ERROR: accessing first element with `non_primitives.get(0)`
 }

tests/ui/get_first.rs

@@ -14,17 +14,20 @@ impl Bar {
 
 fn main() {
     let x = vec![2, 3, 5];
-    let _ = x.get(0); // Use x.first()
+    let _ = x.get(0);
+    //~^ ERROR: accessing first element with `x.get(0)`
     let _ = x.get(1);
     let _ = x[0];
 
     let y = [2, 3, 5];
-    let _ = y.get(0); // Use y.first()
+    let _ = y.get(0);
+    //~^ ERROR: accessing first element with `y.get(0)`
     let _ = y.get(1);
     let _ = y[0];
 
     let z = &[2, 3, 5];
-    let _ = z.get(0); // Use z.first()
+    let _ = z.get(0);
+    //~^ ERROR: accessing first element with `z.get(0)`
     let _ = z.get(1);
     let _ = z[0];
 
@@ -37,4 +40,8 @@ fn main() {
 
     let bar = Bar { arr: [0, 1, 2] };
     let _ = bar.get(0); // Do not lint, because Bar is struct.
+
+    let non_primitives = [vec![1, 2], vec![3, 4]];
+    let _ = non_primitives.get(0);
+    //~^ ERROR: accessing first element with `non_primitives.get(0)`
 }

tests/ui/get_first.stderr

@@ -1,23 +1,29 @@
 error: accessing first element with `x.get(0)`
   --> $DIR/get_first.rs:17:13
    |
-LL |     let _ = x.get(0); // Use x.first()
+LL |     let _ = x.get(0);
    |             ^^^^^^^^ help: try: `x.first()`
    |
    = note: `-D clippy::get-first` implied by `-D warnings`
    = help: to override `-D warnings` add `#[allow(clippy::get_first)]`
 
 error: accessing first element with `y.get(0)`
-  --> $DIR/get_first.rs:22:13
+  --> $DIR/get_first.rs:23:13
    |
-LL |     let _ = y.get(0); // Use y.first()
+LL |     let _ = y.get(0);
    |             ^^^^^^^^ help: try: `y.first()`
 
 error: accessing first element with `z.get(0)`
-  --> $DIR/get_first.rs:27:13
+  --> $DIR/get_first.rs:29:13
    |
-LL |     let _ = z.get(0); // Use z.first()
+LL |     let _ = z.get(0);
    |             ^^^^^^^^ help: try: `z.first()`
 
-error: aborting due to 3 previous errors
+error: accessing first element with `non_primitives.get(0)`
+  --> $DIR/get_first.rs:45:13
+   |
+LL |     let _ = non_primitives.get(0);
+   |             ^^^^^^^^^^^^^^^^^^^^^ help: try: `non_primitives.first()`
+
+error: aborting due to 4 previous errors