From f50ded059272ed3c060ea5df353966384d7df427 Mon Sep 17 00:00:00 2001
From: rail <12975677+rail-rain@users.noreply.github.com>
Date: Thu, 7 Jan 2021 16:41:15 +1300
Subject: [PATCH] Catch `pointer::cast` too in `cast_ptr_alignment`

---
 clippy_lints/src/types.rs      | 35 ++++++++++++++++++++++++++++------
 tests/ui/cast_alignment.rs     |  4 ++++
 tests/ui/cast_alignment.stderr | 14 +++++++++++++-
 3 files changed, 46 insertions(+), 7 deletions(-)

diff --git a/clippy_lints/src/types.rs b/clippy_lints/src/types.rs
index b21f81bd517..2d256b38b0d 100644
--- a/clippy_lints/src/types.rs
+++ b/clippy_lints/src/types.rs
@@ -1637,12 +1637,8 @@ impl<'tcx> LateLintPass<'tcx> for Casts {
             return;
         }
         if let ExprKind::Cast(ref ex, cast_to) = expr.kind {
-            if let TyKind::Path(QPath::Resolved(_, path)) = cast_to.kind {
-                if let Res::Def(_, def_id) = path.res {
-                    if cx.tcx.has_attr(def_id, sym::cfg) || cx.tcx.has_attr(def_id, sym::cfg_attr) {
-                        return;
-                    }
-                }
+            if is_hir_ty_cfg_dependant(cx, cast_to) {
+                return;
             }
             let (cast_from, cast_to) = (cx.typeck_results().expr_ty(ex), cx.typeck_results().expr_ty(expr));
             lint_fn_to_numeric_cast(cx, expr, ex, cast_from, cast_to);
@@ -1691,6 +1687,21 @@ impl<'tcx> LateLintPass<'tcx> for Casts {
                 lint_numeric_casts(cx, expr, ex, cast_from, cast_to);
             }
 
+            lint_cast_ptr_alignment(cx, expr, cast_from, cast_to);
+        } else if let ExprKind::MethodCall(method_path, _, args, _) = expr.kind {
+            if method_path.ident.name != sym!(cast) {
+                return;
+            }
+            if_chain! {
+                if let Some(generic_args) = method_path.args;
+                if let [GenericArg::Type(cast_to)] = generic_args.args;
+                // There probably is no obvious reason to do this, just to be consistent with `as` cases.
+                if is_hir_ty_cfg_dependant(cx, cast_to);
+                then {
+                    return;
+                }
+            }
+            let (cast_from, cast_to) = (cx.typeck_results().expr_ty(&args[0]), cx.typeck_results().expr_ty(expr));
             lint_cast_ptr_alignment(cx, expr, cast_from, cast_to);
         }
     }
@@ -1714,6 +1725,18 @@ fn get_numeric_literal<'e>(expr: &'e Expr<'e>) -> Option<&'e Lit> {
     }
 }
 
+fn is_hir_ty_cfg_dependant(cx: &LateContext<'_>, ty: &hir::Ty<'_>) -> bool {
+    if_chain! {
+        if let TyKind::Path(QPath::Resolved(_, path)) = ty.kind;
+        if let Res::Def(_, def_id) = path.res;
+        then {
+            cx.tcx.has_attr(def_id, sym::cfg) || cx.tcx.has_attr(def_id, sym::cfg_attr)
+        } else {
+            false
+        }
+    }
+}
+
 fn show_unnecessary_cast(cx: &LateContext<'_>, expr: &Expr<'_>, literal_str: &str, cast_from: Ty<'_>, cast_to: Ty<'_>) {
     let literal_kind_name = if cast_from.is_integral() { "integer" } else { "float" };
     span_lint_and_sugg(
diff --git a/tests/ui/cast_alignment.rs b/tests/ui/cast_alignment.rs
index 4c08935639f..d011e84b115 100644
--- a/tests/ui/cast_alignment.rs
+++ b/tests/ui/cast_alignment.rs
@@ -12,6 +12,10 @@ fn main() {
     (&1u8 as *const u8) as *const u16;
     (&mut 1u8 as *mut u8) as *mut u16;
 
+    // cast to more-strictly-aligned type, but with the `pointer::cast` function.
+    (&1u8 as *const u8).cast::<u16>();
+    (&mut 1u8 as *mut u8).cast::<u16>();
+
     /* These should be ok */
 
     // not a pointer type
diff --git a/tests/ui/cast_alignment.stderr b/tests/ui/cast_alignment.stderr
index 79219f86155..97e31c130a9 100644
--- a/tests/ui/cast_alignment.stderr
+++ b/tests/ui/cast_alignment.stderr
@@ -12,5 +12,17 @@ error: casting from `*mut u8` to a more-strictly-aligned pointer (`*mut u16`) (1
 LL |     (&mut 1u8 as *mut u8) as *mut u16;
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
-error: aborting due to 2 previous errors
+error: casting from `*const u8` to a more-strictly-aligned pointer (`*const u16`) (1 < 2 bytes)
+  --> $DIR/cast_alignment.rs:15:5
+   |
+LL |     (&1u8 as *const u8).cast::<u16>();
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: casting from `*mut u8` to a more-strictly-aligned pointer (`*mut u16`) (1 < 2 bytes)
+  --> $DIR/cast_alignment.rs:16:5
+   |
+LL |     (&mut 1u8 as *mut u8).cast::<u16>();
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to 4 previous errors