Auto merge of #7638 - xFrednet:7569-avoid-indexing-in-clippy, r=Manishearth

Avoid slice indexing in Clippy (down with the ICEs)

While working on #7569 I got about 23 lint reports where we can avoid slice indexing by destructing the slice early. This is a preparation PR to avoid fixing them in the lint PR. (The implementation already takes about 300 lines without tests :sweat_smile:). Either way, this should hopefully be easy to review :upside_down_face:

---

changelog: none

18 files changed, 58 insertions, 58 deletions

diff --git a/clippy_lints/src/blocks_in_if_conditions.rs b/clippy_lints/src/blocks_in_if_conditions.rs
index 51d95cc6f0b..47e5b0d583d 100644
--- a/clippy_lints/src/blocks_in_if_conditions.rs
+++ b/clippy_lints/src/blocks_in_if_conditions.rs
@@ -61,8 +61,8 @@ impl<'a, 'tcx> Visitor<'tcx> for ExVisitor<'a, 'tcx> {
             // do not lint if the closure is called using an iterator (see #1141)
             if_chain! {
                 if let Some(parent) = get_parent_expr(self.cx, expr);
-                if let ExprKind::MethodCall(_, _, args, _) = parent.kind;
-                let caller = self.cx.typeck_results().expr_ty(&args[0]);
+                if let ExprKind::MethodCall(_, _, [self_arg, ..], _) = &parent.kind;
+                let caller = self.cx.typeck_results().expr_ty(self_arg);
                 if let Some(iter_id) = self.cx.tcx.get_diagnostic_item(sym::Iterator);
                 if implements_trait(self.cx, caller, iter_id, &[]);
                 then {
diff --git a/clippy_lints/src/casts/cast_ptr_alignment.rs b/clippy_lints/src/casts/cast_ptr_alignment.rs
index 62a119d662b..5880859e719 100644
--- a/clippy_lints/src/casts/cast_ptr_alignment.rs
+++ b/clippy_lints/src/casts/cast_ptr_alignment.rs
@@ -19,7 +19,7 @@ pub(super) fn check(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
             cx.typeck_results().expr_ty(expr),
         );
         lint_cast_ptr_alignment(cx, expr, cast_from, cast_to);
-    } else if let ExprKind::MethodCall(method_path, _, args, _) = expr.kind {
+    } else if let ExprKind::MethodCall(method_path, _, [self_arg, ..], _) = &expr.kind {
         if_chain! {
             if method_path.ident.name == sym!(cast);
             if let Some(generic_args) = method_path.args;
@@ -28,7 +28,7 @@ pub(super) fn check(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
             if !is_hir_ty_cfg_dependant(cx, cast_to);
             then {
                 let (cast_from, cast_to) =
-                    (cx.typeck_results().expr_ty(&args[0]), cx.typeck_results().expr_ty(expr));
+                    (cx.typeck_results().expr_ty(self_arg), cx.typeck_results().expr_ty(expr));
                 lint_cast_ptr_alignment(cx, expr, cast_from, cast_to);
             }
         }
diff --git a/clippy_lints/src/floating_point_arithmetic.rs b/clippy_lints/src/floating_point_arithmetic.rs
index a643b3eb8f1..eda611117ba 100644
--- a/clippy_lints/src/floating_point_arithmetic.rs
+++ b/clippy_lints/src/floating_point_arithmetic.rs
@@ -362,22 +362,22 @@ fn detect_hypot(cx: &LateContext<'_>, args: &[Expr<'_>]) -> Option<String> {
         if_chain! {
             if let ExprKind::MethodCall(
                 PathSegment { ident: lmethod_name, .. },
-                ref _lspan,
-                largs,
+                _lspan,
+                [largs_0, largs_1, ..],
                 _
-            ) = add_lhs.kind;
+            ) = &add_lhs.kind;
             if let ExprKind::MethodCall(
                 PathSegment { ident: rmethod_name, .. },
-                ref _rspan,
-                rargs,
+                _rspan,
+                [rargs_0, rargs_1, ..],
                 _
-            ) = add_rhs.kind;
+            ) = &add_rhs.kind;
             if lmethod_name.as_str() == "powi" && rmethod_name.as_str() == "powi";
-            if let Some((lvalue, _)) = constant(cx, cx.typeck_results(), &largs[1]);
-            if let Some((rvalue, _)) = constant(cx, cx.typeck_results(), &rargs[1]);
+            if let Some((lvalue, _)) = constant(cx, cx.typeck_results(), largs_1);
+            if let Some((rvalue, _)) = constant(cx, cx.typeck_results(), rargs_1);
             if Int(2) == lvalue && Int(2) == rvalue;
             then {
-                return Some(format!("{}.hypot({})", Sugg::hir(cx, &largs[0], ".."), Sugg::hir(cx, &rargs[0], "..")));
+                return Some(format!("{}.hypot({})", Sugg::hir(cx, largs_0, ".."), Sugg::hir(cx, rargs_0, "..")));
             }
         }
     }
@@ -407,8 +407,8 @@ fn check_expm1(cx: &LateContext<'_>, expr: &Expr<'_>) {
         if cx.typeck_results().expr_ty(lhs).is_floating_point();
         if let Some((value, _)) = constant(cx, cx.typeck_results(), rhs);
         if F32(1.0) == value || F64(1.0) == value;
-        if let ExprKind::MethodCall(path, _, method_args, _) = lhs.kind;
-        if cx.typeck_results().expr_ty(&method_args[0]).is_floating_point();
+        if let ExprKind::MethodCall(path, _, [self_arg, ..], _) = &lhs.kind;
+        if cx.typeck_results().expr_ty(self_arg).is_floating_point();
         if path.ident.name.as_str() == "exp";
         then {
             span_lint_and_sugg(
@@ -419,7 +419,7 @@ fn check_expm1(cx: &LateContext<'_>, expr: &Expr<'_>) {
                 "consider using",
                 format!(
                     "{}.exp_m1()",
-                    Sugg::hir(cx, &method_args[0], "..")
+                    Sugg::hir(cx, self_arg, "..")
                 ),
                 Applicability::MachineApplicable,
             );
@@ -617,8 +617,8 @@ fn check_log_division(cx: &LateContext<'_>, expr: &Expr<'_>) {
             rhs,
         ) = &expr.kind;
         if are_same_base_logs(cx, lhs, rhs);
-        if let ExprKind::MethodCall(_, _, largs, _) = lhs.kind;
-        if let ExprKind::MethodCall(_, _, rargs, _) = rhs.kind;
+        if let ExprKind::MethodCall(_, _, [largs_self, ..], _) = &lhs.kind;
+        if let ExprKind::MethodCall(_, _, [rargs_self, ..], _) = &rhs.kind;
         then {
             span_lint_and_sugg(
                 cx,
@@ -626,7 +626,7 @@ fn check_log_division(cx: &LateContext<'_>, expr: &Expr<'_>) {
                 expr.span,
                 "log base can be expressed more clearly",
                 "consider using",
-                format!("{}.log({})", Sugg::hir(cx, &largs[0], ".."), Sugg::hir(cx, &rargs[0], ".."),),
+                format!("{}.log({})", Sugg::hir(cx, largs_self, ".."), Sugg::hir(cx, rargs_self, ".."),),
                 Applicability::MachineApplicable,
             );
         }
diff --git a/clippy_lints/src/if_let_mutex.rs b/clippy_lints/src/if_let_mutex.rs
index 7dad1c31150..ef72b88b3c7 100644
--- a/clippy_lints/src/if_let_mutex.rs
+++ b/clippy_lints/src/if_let_mutex.rs
@@ -138,12 +138,12 @@ impl<'tcx, 'l> ArmVisitor<'tcx, 'l> {
 
 fn is_mutex_lock_call<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) -> Option<&'tcx Expr<'tcx>> {
     if_chain! {
-        if let ExprKind::MethodCall(path, _span, args, _) = &expr.kind;
+        if let ExprKind::MethodCall(path, _span, [self_arg, ..], _) = &expr.kind;
         if path.ident.as_str() == "lock";
-        let ty = cx.typeck_results().expr_ty(&args[0]);
+        let ty = cx.typeck_results().expr_ty(self_arg);
         if is_type_diagnostic_item(cx, ty, sym!(mutex_type));
         then {
-            Some(&args[0])
+            Some(self_arg)
         } else {
             None
         }
diff --git a/clippy_lints/src/if_let_some_result.rs b/clippy_lints/src/if_let_some_result.rs
index 33eba02dae0..adcd78ed0d4 100644
--- a/clippy_lints/src/if_let_some_result.rs
+++ b/clippy_lints/src/if_let_some_result.rs
@@ -46,10 +46,10 @@ impl<'tcx> LateLintPass<'tcx> for OkIfLet {
     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
         if_chain! { //begin checking variables
             if let Some(higher::IfLet { let_pat, let_expr, .. }) = higher::IfLet::hir(cx, expr);
-            if let ExprKind::MethodCall(_, ok_span, result_types, _) = let_expr.kind; //check is expr.ok() has type Result<T,E>.ok(, _)
+            if let ExprKind::MethodCall(_, ok_span, [ref result_types_0, ..], _) = let_expr.kind; //check is expr.ok() has type Result<T,E>.ok(, _)
             if let PatKind::TupleStruct(QPath::Resolved(_, x), y, _)  = let_pat.kind; //get operation
             if method_chain_args(let_expr, &["ok"]).is_some(); //test to see if using ok() methoduse std::marker::Sized;
-            if is_type_diagnostic_item(cx, cx.typeck_results().expr_ty(&result_types[0]), sym::result_type);
+            if is_type_diagnostic_item(cx, cx.typeck_results().expr_ty(result_types_0), sym::result_type);
             if rustc_hir_pretty::to_string(rustc_hir_pretty::NO_ANN, |s| s.print_path(x, false)) == "Some";
 
             then {
diff --git a/clippy_lints/src/loops/needless_range_loop.rs b/clippy_lints/src/loops/needless_range_loop.rs
index f17e76d9682..e8f3550283a 100644
--- a/clippy_lints/src/loops/needless_range_loop.rs
+++ b/clippy_lints/src/loops/needless_range_loop.rs
@@ -301,10 +301,10 @@ impl<'a, 'tcx> Visitor<'tcx> for VarVisitor<'a, 'tcx> {
     fn visit_expr(&mut self, expr: &'tcx Expr<'_>) {
         if_chain! {
             // a range index op
-            if let ExprKind::MethodCall(meth, _, args, _) = expr.kind;
+            if let ExprKind::MethodCall(meth, _, [args_0, args_1, ..], _) = &expr.kind;
             if (meth.ident.name == sym::index && match_trait_method(self.cx, expr, &paths::INDEX))
                 || (meth.ident.name == sym::index_mut && match_trait_method(self.cx, expr, &paths::INDEX_MUT));
-            if !self.check(&args[1], &args[0], expr);
+            if !self.check(args_1, args_0, expr);
             then { return }
         }
 
diff --git a/clippy_lints/src/mem_forget.rs b/clippy_lints/src/mem_forget.rs
index 07202a59c4b..eb437dc47af 100644
--- a/clippy_lints/src/mem_forget.rs
+++ b/clippy_lints/src/mem_forget.rs
@@ -28,11 +28,11 @@ declare_lint_pass!(MemForget => [MEM_FORGET]);
 
 impl<'tcx> LateLintPass<'tcx> for MemForget {
     fn check_expr(&mut self, cx: &LateContext<'tcx>, e: &'tcx Expr<'_>) {
-        if let ExprKind::Call(path_expr, args) = e.kind {
+        if let ExprKind::Call(path_expr, [ref first_arg, ..]) = e.kind {
             if let ExprKind::Path(ref qpath) = path_expr.kind {
                 if let Some(def_id) = cx.qpath_res(qpath, path_expr.hir_id).opt_def_id() {
                     if match_def_path(cx, def_id, &paths::MEM_FORGET) {
-                        let forgot_ty = cx.typeck_results().expr_ty(&args[0]);
+                        let forgot_ty = cx.typeck_results().expr_ty(first_arg);
 
                         if forgot_ty.ty_adt_def().map_or(false, |def| def.has_dtor(cx.tcx)) {
                             span_lint(cx, MEM_FORGET, e.span, "usage of `mem::forget` on `Drop` type");
diff --git a/clippy_lints/src/methods/or_fun_call.rs b/clippy_lints/src/methods/or_fun_call.rs
index c1d22e5d72c..30ed1d665a9 100644
--- a/clippy_lints/src/methods/or_fun_call.rs
+++ b/clippy_lints/src/methods/or_fun_call.rs
@@ -96,9 +96,9 @@ pub(super) fn check<'tcx>(
             (&paths::RESULT, true, &["or", "unwrap_or"], "else"),
         ];
 
-        if let hir::ExprKind::MethodCall(path, _, args, _) = &arg.kind {
+        if let hir::ExprKind::MethodCall(path, _, [self_arg, ..], _) = &arg.kind {
             if path.ident.name == sym::len {
-                let ty = cx.typeck_results().expr_ty(&args[0]).peel_refs();
+                let ty = cx.typeck_results().expr_ty(self_arg).peel_refs();
 
                 match ty.kind() {
                     ty::Slice(_) | ty::Array(_, _) | ty::Str => return,
diff --git a/clippy_lints/src/methods/utils.rs b/clippy_lints/src/methods/utils.rs
index 0daea47816a..30d6665a920 100644
--- a/clippy_lints/src/methods/utils.rs
+++ b/clippy_lints/src/methods/utils.rs
@@ -24,9 +24,9 @@ pub(super) fn derefs_to_slice<'tcx>(
         }
     }
 
-    if let hir::ExprKind::MethodCall(path, _, args, _) = expr.kind {
-        if path.ident.name == sym::iter && may_slice(cx, cx.typeck_results().expr_ty(&args[0])) {
-            Some(&args[0])
+    if let hir::ExprKind::MethodCall(path, _, [self_arg, ..], _) = &expr.kind {
+        if path.ident.name == sym::iter && may_slice(cx, cx.typeck_results().expr_ty(self_arg)) {
+            Some(self_arg)
         } else {
             None
         }
diff --git a/clippy_lints/src/misc.rs b/clippy_lints/src/misc.rs
index c796abe9815..538fa4e1678 100644
--- a/clippy_lints/src/misc.rs
+++ b/clippy_lints/src/misc.rs
@@ -513,12 +513,12 @@ fn is_signum(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
     }
 
     if_chain! {
-        if let ExprKind::MethodCall(method_name, _, expressions, _) = expr.kind;
+        if let ExprKind::MethodCall(method_name, _, [ref self_arg, ..], _) = expr.kind;
         if sym!(signum) == method_name.ident.name;
         // Check that the receiver of the signum() is a float (expressions[0] is the receiver of
         // the method call)
         then {
-            return is_float(cx, &expressions[0]);
+            return is_float(cx, self_arg);
         }
     }
     false
diff --git a/clippy_lints/src/mut_mutex_lock.rs b/clippy_lints/src/mut_mutex_lock.rs
index 85e870632a5..e9dcc7b227d 100644
--- a/clippy_lints/src/mut_mutex_lock.rs
+++ b/clippy_lints/src/mut_mutex_lock.rs
@@ -47,9 +47,9 @@ declare_lint_pass!(MutMutexLock => [MUT_MUTEX_LOCK]);
 impl<'tcx> LateLintPass<'tcx> for MutMutexLock {
     fn check_expr(&mut self, cx: &LateContext<'tcx>, ex: &'tcx Expr<'tcx>) {
         if_chain! {
-            if let ExprKind::MethodCall(path, method_span, args, _) = &ex.kind;
+            if let ExprKind::MethodCall(path, method_span, [self_arg, ..], _) = &ex.kind;
             if path.ident.name == sym!(lock);
-            let ty = cx.typeck_results().expr_ty(&args[0]);
+            let ty = cx.typeck_results().expr_ty(self_arg);
             if let ty::Ref(_, inner_ty, Mutability::Mut) = ty.kind();
             if is_type_diagnostic_item(cx, inner_ty, sym!(mutex_type));
             then {
diff --git a/clippy_lints/src/open_options.rs b/clippy_lints/src/open_options.rs
index 4064d94da2a..5752342cf62 100644
--- a/clippy_lints/src/open_options.rs
+++ b/clippy_lints/src/open_options.rs
@@ -31,11 +31,11 @@ declare_lint_pass!(OpenOptions => [NONSENSICAL_OPEN_OPTIONS]);
 
 impl<'tcx> LateLintPass<'tcx> for OpenOptions {
     fn check_expr(&mut self, cx: &LateContext<'tcx>, e: &'tcx Expr<'_>) {
-        if let ExprKind::MethodCall(path, _, arguments, _) = e.kind {
-            let obj_ty = cx.typeck_results().expr_ty(&arguments[0]).peel_refs();
+        if let ExprKind::MethodCall(path, _, [self_arg, ..], _) = &e.kind {
+            let obj_ty = cx.typeck_results().expr_ty(self_arg).peel_refs();
             if path.ident.name == sym!(open) && match_type(cx, obj_ty, &paths::OPEN_OPTIONS) {
                 let mut options = Vec::new();
-                get_open_options(cx, &arguments[0], &mut options);
+                get_open_options(cx, self_arg, &mut options);
                 check_open_options(cx, &options, e.span);
             }
         }
diff --git a/clippy_lints/src/ptr_offset_with_cast.rs b/clippy_lints/src/ptr_offset_with_cast.rs
index f1975056ddc..cfb5287c667 100644
--- a/clippy_lints/src/ptr_offset_with_cast.rs
+++ b/clippy_lints/src/ptr_offset_with_cast.rs
@@ -92,13 +92,13 @@ fn expr_as_ptr_offset_call<'tcx>(
     cx: &LateContext<'tcx>,
     expr: &'tcx Expr<'_>,
 ) -> Option<(&'tcx Expr<'tcx>, &'tcx Expr<'tcx>, Method)> {
-    if let ExprKind::MethodCall(path_segment, _, args, _) = expr.kind {
-        if is_expr_ty_raw_ptr(cx, &args[0]) {
+    if let ExprKind::MethodCall(path_segment, _, [arg_0, arg_1, ..], _) = &expr.kind {
+        if is_expr_ty_raw_ptr(cx, arg_0) {
             if path_segment.ident.name == sym::offset {
-                return Some((&args[0], &args[1], Method::Offset));
+                return Some((arg_0, arg_1, Method::Offset));
             }
             if path_segment.ident.name == sym!(wrapping_offset) {
-                return Some((&args[0], &args[1], Method::WrappingOffset));
+                return Some((arg_0, arg_1, Method::WrappingOffset));
             }
         }
     }
diff --git a/clippy_lints/src/strings.rs b/clippy_lints/src/strings.rs
index 1a78a4968e5..13d8f954c44 100644
--- a/clippy_lints/src/strings.rs
+++ b/clippy_lints/src/strings.rs
@@ -345,9 +345,9 @@ declare_lint_pass!(StrToString => [STR_TO_STRING]);
 impl LateLintPass<'_> for StrToString {
     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &Expr<'_>) {
         if_chain! {
-            if let ExprKind::MethodCall(path, _, args, _) = &expr.kind;
+            if let ExprKind::MethodCall(path, _, [self_arg, ..], _) = &expr.kind;
             if path.ident.name == sym!(to_string);
-            let ty = cx.typeck_results().expr_ty(&args[0]);
+            let ty = cx.typeck_results().expr_ty(self_arg);
             if let ty::Ref(_, ty, ..) = ty.kind();
             if *ty.kind() == ty::Str;
             then {
@@ -394,9 +394,9 @@ declare_lint_pass!(StringToString => [STRING_TO_STRING]);
 impl LateLintPass<'_> for StringToString {
     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &Expr<'_>) {
         if_chain! {
-            if let ExprKind::MethodCall(path, _, args, _) = &expr.kind;
+            if let ExprKind::MethodCall(path, _, [self_arg, ..], _) = &expr.kind;
             if path.ident.name == sym!(to_string);
-            let ty = cx.typeck_results().expr_ty(&args[0]);
+            let ty = cx.typeck_results().expr_ty(self_arg);
             if is_type_diagnostic_item(cx, ty, sym::string_type);
             then {
                 span_lint_and_help(
diff --git a/clippy_lints/src/to_string_in_display.rs b/clippy_lints/src/to_string_in_display.rs
index b036ed9a3d2..b7414cec87c 100644
--- a/clippy_lints/src/to_string_in_display.rs
+++ b/clippy_lints/src/to_string_in_display.rs
@@ -92,11 +92,11 @@ impl LateLintPass<'_> for ToStringInDisplay {
         if_chain! {
             if self.in_display_impl;
             if let Some(self_hir_id) = self.self_hir_id;
-            if let ExprKind::MethodCall(path, _, args, _) = expr.kind;
+            if let ExprKind::MethodCall(path, _, [ref self_arg, ..], _) = expr.kind;
             if path.ident.name == sym!(to_string);
             if let Some(expr_def_id) = cx.typeck_results().type_dependent_def_id(expr.hir_id);
             if is_diag_trait_item(cx, expr_def_id, sym::ToString);
-            if path_to_local_id(&args[0], self_hir_id);
+            if path_to_local_id(self_arg, self_hir_id);
             then {
                 span_lint(
                     cx,
diff --git a/clippy_lints/src/undropped_manually_drops.rs b/clippy_lints/src/undropped_manually_drops.rs
index 47571e608c7..09570616593 100644
--- a/clippy_lints/src/undropped_manually_drops.rs
+++ b/clippy_lints/src/undropped_manually_drops.rs
@@ -37,8 +37,8 @@ declare_lint_pass!(UndroppedManuallyDrops => [UNDROPPED_MANUALLY_DROPS]);
 
 impl LateLintPass<'tcx> for UndroppedManuallyDrops {
     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
-        if let Some(args) = match_function_call(cx, expr, &paths::DROP) {
-            let ty = cx.typeck_results().expr_ty(&args[0]);
+        if let Some([arg_0, ..]) = match_function_call(cx, expr, &paths::DROP) {
+            let ty = cx.typeck_results().expr_ty(arg_0);
             if is_type_lang_item(cx, ty, lang_items::LangItem::ManuallyDrop) {
                 span_lint_and_help(
                     cx,
diff --git a/clippy_lints/src/unused_io_amount.rs b/clippy_lints/src/unused_io_amount.rs
index 82bc4a6d153..031b182bd2f 100644
--- a/clippy_lints/src/unused_io_amount.rs
+++ b/clippy_lints/src/unused_io_amount.rs
@@ -45,20 +45,20 @@ impl<'tcx> LateLintPass<'tcx> for UnusedIoAmount {
 
         match expr.kind {
             hir::ExprKind::Match(res, _, _) if is_try(cx, expr).is_some() => {
-                if let hir::ExprKind::Call(func, args) = res.kind {
+                if let hir::ExprKind::Call(func, [ref arg_0, ..]) = res.kind {
                     if matches!(
                         func.kind,
                         hir::ExprKind::Path(hir::QPath::LangItem(hir::LangItem::TryTraitBranch, _))
                     ) {
-                        check_map_error(cx, &args[0], expr);
+                        check_map_error(cx, arg_0, expr);
                     }
                 } else {
                     check_map_error(cx, res, expr);
                 }
             },
-            hir::ExprKind::MethodCall(path, _, args, _) => match &*path.ident.as_str() {
+            hir::ExprKind::MethodCall(path, _, [ref arg_0, ..], _) => match &*path.ident.as_str() {
                 "expect" | "unwrap" | "unwrap_or" | "unwrap_or_else" => {
-                    check_map_error(cx, &args[0], expr);
+                    check_map_error(cx, arg_0, expr);
                 },
                 _ => (),
             },
diff --git a/clippy_lints/src/utils/internal_lints.rs b/clippy_lints/src/utils/internal_lints.rs
index 42d51272279..756c33d70c2 100644
--- a/clippy_lints/src/utils/internal_lints.rs
+++ b/clippy_lints/src/utils/internal_lints.rs
@@ -504,10 +504,10 @@ impl<'tcx> LateLintPass<'tcx> for CompilerLintFunctions {
         }
 
         if_chain! {
-            if let ExprKind::MethodCall(path, _, args, _) = expr.kind;
+            if let ExprKind::MethodCall(path, _, [self_arg, ..], _) = &expr.kind;
             let fn_name = path.ident;
             if let Some(sugg) = self.map.get(&*fn_name.as_str());
-            let ty = cx.typeck_results().expr_ty(&args[0]).peel_refs();
+            let ty = cx.typeck_results().expr_ty(self_arg).peel_refs();
             if match_type(cx, ty, &paths::EARLY_CONTEXT)
                 || match_type(cx, ty, &paths::LATE_CONTEXT);
             then {