Merge commit '6ed6f1e6a1a8f414ba7e6d9b8222e7e5a1686e42' into clippyup

14 files changed, 1123 insertions, 0 deletions

diff --git a/clippy_lints/src/casts/cast_lossless.rs b/clippy_lints/src/casts/cast_lossless.rs
new file mode 100644
index 00000000000..478832a5164
--- /dev/null
+++ b/clippy_lints/src/casts/cast_lossless.rs
@@ -0,0 +1,87 @@
+use rustc_errors::Applicability;
+use rustc_hir::{Expr, ExprKind};
+use rustc_lint::LateContext;
+use rustc_middle::ty::{self, FloatTy, Ty};
+
+use crate::utils::{in_constant, is_isize_or_usize, snippet_opt, span_lint_and_sugg};
+
+use super::{utils, CAST_LOSSLESS};
+
+pub(super) fn check(cx: &LateContext<'_>, expr: &Expr<'_>, cast_op: &Expr<'_>, cast_from: Ty<'_>, cast_to: Ty<'_>) {
+    if !should_lint(cx, expr, cast_from, cast_to) {
+        return;
+    }
+
+    // The suggestion is to use a function call, so if the original expression
+    // has parens on the outside, they are no longer needed.
+    let mut applicability = Applicability::MachineApplicable;
+    let opt = snippet_opt(cx, cast_op.span);
+    let sugg = opt.as_ref().map_or_else(
+        || {
+            applicability = Applicability::HasPlaceholders;
+            ".."
+        },
+        |snip| {
+            if should_strip_parens(cast_op, snip) {
+                &snip[1..snip.len() - 1]
+            } else {
+                snip.as_str()
+            }
+        },
+    );
+
+    span_lint_and_sugg(
+        cx,
+        CAST_LOSSLESS,
+        expr.span,
+        &format!(
+            "casting `{}` to `{}` may become silently lossy if you later change the type",
+            cast_from, cast_to
+        ),
+        "try",
+        format!("{}::from({})", cast_to, sugg),
+        applicability,
+    );
+}
+
+fn should_lint(cx: &LateContext<'_>, expr: &Expr<'_>, cast_from: Ty<'_>, cast_to: Ty<'_>) -> bool {
+    // Do not suggest using From in consts/statics until it is valid to do so (see #2267).
+    if in_constant(cx, expr.hir_id) {
+        return false;
+    }
+
+    match (cast_from.is_integral(), cast_to.is_integral()) {
+        (true, true) => {
+            let cast_signed_to_unsigned = cast_from.is_signed() && !cast_to.is_signed();
+            let from_nbits = utils::int_ty_to_nbits(cast_from, cx.tcx);
+            let to_nbits = utils::int_ty_to_nbits(cast_to, cx.tcx);
+            !is_isize_or_usize(cast_from)
+                && !is_isize_or_usize(cast_to)
+                && from_nbits < to_nbits
+                && !cast_signed_to_unsigned
+        },
+
+        (true, false) => {
+            let from_nbits = utils::int_ty_to_nbits(cast_from, cx.tcx);
+            let to_nbits = if let ty::Float(FloatTy::F32) = cast_to.kind() {
+                32
+            } else {
+                64
+            };
+            from_nbits < to_nbits
+        },
+
+        (_, _) => {
+            matches!(cast_from.kind(), ty::Float(FloatTy::F32)) && matches!(cast_to.kind(), ty::Float(FloatTy::F64))
+        },
+    }
+}
+
+fn should_strip_parens(cast_expr: &Expr<'_>, snip: &str) -> bool {
+    if let ExprKind::Binary(_, _, _) = cast_expr.kind {
+        if snip.starts_with('(') && snip.ends_with(')') {
+            return true;
+        }
+    }
+    false
+}
diff --git a/clippy_lints/src/casts/cast_possible_truncation.rs b/clippy_lints/src/casts/cast_possible_truncation.rs
new file mode 100644
index 00000000000..33b06b8fe7c
--- /dev/null
+++ b/clippy_lints/src/casts/cast_possible_truncation.rs
@@ -0,0 +1,54 @@
+use rustc_hir::Expr;
+use rustc_lint::LateContext;
+use rustc_middle::ty::{self, FloatTy, Ty};
+
+use crate::utils::{is_isize_or_usize, span_lint};
+
+use super::{utils, CAST_POSSIBLE_TRUNCATION};
+
+pub(super) fn check(cx: &LateContext<'_>, expr: &Expr<'_>, cast_from: Ty<'_>, cast_to: Ty<'_>) {
+    let msg = match (cast_from.is_integral(), cast_to.is_integral()) {
+        (true, true) => {
+            let from_nbits = utils::int_ty_to_nbits(cast_from, cx.tcx);
+            let to_nbits = utils::int_ty_to_nbits(cast_to, cx.tcx);
+
+            let (should_lint, suffix) = match (is_isize_or_usize(cast_from), is_isize_or_usize(cast_to)) {
+                (true, true) | (false, false) => (to_nbits < from_nbits, ""),
+                (true, false) => (
+                    to_nbits <= 32,
+                    if to_nbits == 32 {
+                        " on targets with 64-bit wide pointers"
+                    } else {
+                        ""
+                    },
+                ),
+                (false, true) => (from_nbits == 64, " on targets with 32-bit wide pointers"),
+            };
+
+            if !should_lint {
+                return;
+            }
+
+            format!(
+                "casting `{}` to `{}` may truncate the value{}",
+                cast_from, cast_to, suffix,
+            )
+        },
+
+        (false, true) => {
+            format!("casting `{}` to `{}` may truncate the value", cast_from, cast_to)
+        },
+
+        (_, _) => {
+            if matches!(cast_from.kind(), &ty::Float(FloatTy::F64))
+                && matches!(cast_to.kind(), &ty::Float(FloatTy::F32))
+            {
+                "casting `f64` to `f32` may truncate the value".to_string()
+            } else {
+                return;
+            }
+        },
+    };
+
+    span_lint(cx, CAST_POSSIBLE_TRUNCATION, expr.span, &msg);
+}
diff --git a/clippy_lints/src/casts/cast_possible_wrap.rs b/clippy_lints/src/casts/cast_possible_wrap.rs
new file mode 100644
index 00000000000..56d301ed3e1
--- /dev/null
+++ b/clippy_lints/src/casts/cast_possible_wrap.rs
@@ -0,0 +1,44 @@
+use rustc_hir::Expr;
+use rustc_lint::LateContext;
+use rustc_middle::ty::Ty;
+
+use crate::utils::{is_isize_or_usize, span_lint};
+
+use super::{utils, CAST_POSSIBLE_WRAP};
+
+pub(super) fn check(cx: &LateContext<'_>, expr: &Expr<'_>, cast_from: Ty<'_>, cast_to: Ty<'_>) {
+    if !(cast_from.is_integral() && cast_to.is_integral()) {
+        return;
+    }
+
+    let arch_64_suffix = " on targets with 64-bit wide pointers";
+    let arch_32_suffix = " on targets with 32-bit wide pointers";
+    let cast_unsigned_to_signed = !cast_from.is_signed() && cast_to.is_signed();
+    let from_nbits = utils::int_ty_to_nbits(cast_from, cx.tcx);
+    let to_nbits = utils::int_ty_to_nbits(cast_to, cx.tcx);
+
+    let (should_lint, suffix) = match (is_isize_or_usize(cast_from), is_isize_or_usize(cast_to)) {
+        (true, true) | (false, false) => (to_nbits == from_nbits && cast_unsigned_to_signed, ""),
+        (true, false) => (to_nbits <= 32 && cast_unsigned_to_signed, arch_32_suffix),
+        (false, true) => (
+            cast_unsigned_to_signed,
+            if from_nbits == 64 {
+                arch_64_suffix
+            } else {
+                arch_32_suffix
+            },
+        ),
+    };
+
+    if should_lint {
+        span_lint(
+            cx,
+            CAST_POSSIBLE_WRAP,
+            expr.span,
+            &format!(
+                "casting `{}` to `{}` may wrap around the value{}",
+                cast_from, cast_to, suffix,
+            ),
+        );
+    }
+}
diff --git a/clippy_lints/src/casts/cast_precision_loss.rs b/clippy_lints/src/casts/cast_precision_loss.rs
new file mode 100644
index 00000000000..a1c3900ce1f
--- /dev/null
+++ b/clippy_lints/src/casts/cast_precision_loss.rs
@@ -0,0 +1,51 @@
+use rustc_hir::Expr;
+use rustc_lint::LateContext;
+use rustc_middle::ty::{self, FloatTy, Ty};
+
+use crate::utils::{is_isize_or_usize, span_lint};
+
+use super::{utils, CAST_PRECISION_LOSS};
+
+pub(super) fn check(cx: &LateContext<'_>, expr: &Expr<'_>, cast_from: Ty<'_>, cast_to: Ty<'_>) {
+    if !cast_from.is_integral() || cast_to.is_integral() {
+        return;
+    }
+
+    let from_nbits = utils::int_ty_to_nbits(cast_from, cx.tcx);
+    let to_nbits = if let ty::Float(FloatTy::F32) = cast_to.kind() {
+        32
+    } else {
+        64
+    };
+
+    if !(is_isize_or_usize(cast_from) || from_nbits >= to_nbits) {
+        return;
+    }
+
+    let cast_to_f64 = to_nbits == 64;
+    let mantissa_nbits = if cast_to_f64 { 52 } else { 23 };
+    let arch_dependent = is_isize_or_usize(cast_from) && cast_to_f64;
+    let arch_dependent_str = "on targets with 64-bit wide pointers ";
+    let from_nbits_str = if arch_dependent {
+        "64".to_owned()
+    } else if is_isize_or_usize(cast_from) {
+        "32 or 64".to_owned()
+    } else {
+        utils::int_ty_to_nbits(cast_from, cx.tcx).to_string()
+    };
+
+    span_lint(
+        cx,
+        CAST_PRECISION_LOSS,
+        expr.span,
+        &format!(
+            "casting `{0}` to `{1}` causes a loss of precision {2}(`{0}` is {3} bits wide, \
+             but `{1}`'s mantissa is only {4} bits wide)",
+            cast_from,
+            if cast_to_f64 { "f64" } else { "f32" },
+            if arch_dependent { arch_dependent_str } else { "" },
+            from_nbits_str,
+            mantissa_nbits
+        ),
+    );
+}
diff --git a/clippy_lints/src/casts/cast_ptr_alignment.rs b/clippy_lints/src/casts/cast_ptr_alignment.rs
new file mode 100644
index 00000000000..87fb5557be0
--- /dev/null
+++ b/clippy_lints/src/casts/cast_ptr_alignment.rs
@@ -0,0 +1,81 @@
+use rustc_hir::{Expr, ExprKind, GenericArg};
+use rustc_lint::LateContext;
+use rustc_middle::ty::{self, Ty};
+use rustc_span::symbol::sym;
+use rustc_target::abi::LayoutOf;
+
+use if_chain::if_chain;
+
+use crate::utils::{is_hir_ty_cfg_dependant, span_lint};
+
+use super::CAST_PTR_ALIGNMENT;
+
+pub(super) fn check(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
+    if let ExprKind::Cast(ref cast_expr, cast_to) = expr.kind {
+        if is_hir_ty_cfg_dependant(cx, cast_to) {
+            return;
+        }
+        let (cast_from, cast_to) = (
+            cx.typeck_results().expr_ty(cast_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 {
+        if_chain! {
+            if method_path.ident.name == sym!(cast);
+            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 {
+                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);
+            }
+        }
+    }
+}
+
+fn lint_cast_ptr_alignment<'tcx>(cx: &LateContext<'tcx>, expr: &Expr<'_>, cast_from: Ty<'tcx>, cast_to: Ty<'tcx>) {
+    if_chain! {
+        if let ty::RawPtr(from_ptr_ty) = &cast_from.kind();
+        if let ty::RawPtr(to_ptr_ty) = &cast_to.kind();
+        if let Ok(from_layout) = cx.layout_of(from_ptr_ty.ty);
+        if let Ok(to_layout) = cx.layout_of(to_ptr_ty.ty);
+        if from_layout.align.abi < to_layout.align.abi;
+        // with c_void, we inherently need to trust the user
+        if !is_c_void(cx, from_ptr_ty.ty);
+        // when casting from a ZST, we don't know enough to properly lint
+        if !from_layout.is_zst();
+        then {
+            span_lint(
+                cx,
+                CAST_PTR_ALIGNMENT,
+                expr.span,
+                &format!(
+                    "casting from `{}` to a more-strictly-aligned pointer (`{}`) ({} < {} bytes)",
+                    cast_from,
+                    cast_to,
+                    from_layout.align.abi.bytes(),
+                    to_layout.align.abi.bytes(),
+                ),
+            );
+        }
+    }
+}
+
+/// Check if the given type is either `core::ffi::c_void` or
+/// one of the platform specific `libc::<platform>::c_void` of libc.
+fn is_c_void(cx: &LateContext<'_>, ty: Ty<'_>) -> bool {
+    if let ty::Adt(adt, _) = ty.kind() {
+        let names = cx.get_def_path(adt.did);
+
+        if names.is_empty() {
+            return false;
+        }
+        if names[0] == sym::libc || names[0] == sym::core && *names.last().unwrap() == sym!(c_void) {
+            return true;
+        }
+    }
+    false
+}
diff --git a/clippy_lints/src/casts/cast_ref_to_mut.rs b/clippy_lints/src/casts/cast_ref_to_mut.rs
new file mode 100644
index 00000000000..3fdc1c6168b
--- /dev/null
+++ b/clippy_lints/src/casts/cast_ref_to_mut.rs
@@ -0,0 +1,28 @@
+use rustc_hir::{Expr, ExprKind, MutTy, Mutability, TyKind, UnOp};
+use rustc_lint::LateContext;
+use rustc_middle::ty;
+
+use if_chain::if_chain;
+
+use crate::utils::span_lint;
+
+use super::CAST_REF_TO_MUT;
+
+pub(super) fn check(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
+    if_chain! {
+        if let ExprKind::Unary(UnOp::Deref, e) = &expr.kind;
+        if let ExprKind::Cast(e, t) = &e.kind;
+        if let TyKind::Ptr(MutTy { mutbl: Mutability::Mut, .. }) = t.kind;
+        if let ExprKind::Cast(e, t) = &e.kind;
+        if let TyKind::Ptr(MutTy { mutbl: Mutability::Not, .. }) = t.kind;
+        if let ty::Ref(..) = cx.typeck_results().node_type(e.hir_id).kind();
+        then {
+            span_lint(
+                cx,
+                CAST_REF_TO_MUT,
+                expr.span,
+                "casting `&T` to `&mut T` may cause undefined behavior, consider instead using an `UnsafeCell`",
+            );
+        }
+    }
+}
diff --git a/clippy_lints/src/casts/cast_sign_loss.rs b/clippy_lints/src/casts/cast_sign_loss.rs
new file mode 100644
index 00000000000..9656fbebd77
--- /dev/null
+++ b/clippy_lints/src/casts/cast_sign_loss.rs
@@ -0,0 +1,70 @@
+use rustc_hir::{Expr, ExprKind};
+use rustc_lint::LateContext;
+use rustc_middle::ty::{self, Ty};
+
+use if_chain::if_chain;
+
+use crate::consts::{constant, Constant};
+use crate::utils::{method_chain_args, sext, span_lint};
+
+use super::CAST_SIGN_LOSS;
+
+pub(super) fn check(cx: &LateContext<'_>, expr: &Expr<'_>, cast_op: &Expr<'_>, cast_from: Ty<'_>, cast_to: Ty<'_>) {
+    if should_lint(cx, cast_op, cast_from, cast_to) {
+        span_lint(
+            cx,
+            CAST_SIGN_LOSS,
+            expr.span,
+            &format!(
+                "casting `{}` to `{}` may lose the sign of the value",
+                cast_from, cast_to
+            ),
+        );
+    }
+}
+
+fn should_lint(cx: &LateContext<'_>, cast_op: &Expr<'_>, cast_from: Ty<'_>, cast_to: Ty<'_>) -> bool {
+    match (cast_from.is_integral(), cast_to.is_integral()) {
+        (true, true) => {
+            if !cast_from.is_signed() || cast_to.is_signed() {
+                return false;
+            }
+
+            // Don't lint for positive constants.
+            let const_val = constant(cx, &cx.typeck_results(), cast_op);
+            if_chain! {
+                if let Some((Constant::Int(n), _)) = const_val;
+                if let ty::Int(ity) = *cast_from.kind();
+                if sext(cx.tcx, n, ity) >= 0;
+                then {
+                    return false;
+                }
+            }
+
+            // Don't lint for the result of methods that always return non-negative values.
+            if let ExprKind::MethodCall(ref path, _, _, _) = cast_op.kind {
+                let mut method_name = path.ident.name.as_str();
+                let allowed_methods = ["abs", "checked_abs", "rem_euclid", "checked_rem_euclid"];
+
+                if_chain! {
+                    if method_name == "unwrap";
+                    if let Some(arglist) = method_chain_args(cast_op, &["unwrap"]);
+                    if let ExprKind::MethodCall(ref inner_path, _, _, _) = &arglist[0][0].kind;
+                    then {
+                        method_name = inner_path.ident.name.as_str();
+                    }
+                }
+
+                if allowed_methods.iter().any(|&name| method_name == name) {
+                    return false;
+                }
+            }
+
+            true
+        },
+
+        (false, true) => !cast_to.is_signed(),
+
+        (_, _) => false,
+    }
+}
diff --git a/clippy_lints/src/casts/char_lit_as_u8.rs b/clippy_lints/src/casts/char_lit_as_u8.rs
new file mode 100644
index 00000000000..ccaad1b8f2a
--- /dev/null
+++ b/clippy_lints/src/casts/char_lit_as_u8.rs
@@ -0,0 +1,42 @@
+use rustc_ast::LitKind;
+use rustc_errors::Applicability;
+use rustc_hir::{Expr, ExprKind};
+use rustc_lint::LateContext;
+use rustc_middle::ty::{self, UintTy};
+
+use if_chain::if_chain;
+
+use crate::utils::{snippet_with_applicability, span_lint_and_then};
+
+use super::CHAR_LIT_AS_U8;
+
+pub(super) fn check(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
+    if_chain! {
+        if let ExprKind::Cast(e, _) = &expr.kind;
+        if let ExprKind::Lit(l) = &e.kind;
+        if let LitKind::Char(c) = l.node;
+        if ty::Uint(UintTy::U8) == *cx.typeck_results().expr_ty(expr).kind();
+        then {
+            let mut applicability = Applicability::MachineApplicable;
+            let snippet = snippet_with_applicability(cx, e.span, "'x'", &mut applicability);
+
+            span_lint_and_then(
+                cx,
+                CHAR_LIT_AS_U8,
+                expr.span,
+                "casting a character literal to `u8` truncates",
+                |diag| {
+                    diag.note("`char` is four bytes wide, but `u8` is a single byte");
+
+                    if c.is_ascii() {
+                        diag.span_suggestion(
+                            expr.span,
+                            "use a byte literal instead",
+                            format!("b{}", snippet),
+                            applicability,
+                        );
+                    }
+            });
+        }
+    }
+}
diff --git a/clippy_lints/src/casts/fn_to_numeric_cast.rs b/clippy_lints/src/casts/fn_to_numeric_cast.rs
new file mode 100644
index 00000000000..a8d508585b5
--- /dev/null
+++ b/clippy_lints/src/casts/fn_to_numeric_cast.rs
@@ -0,0 +1,37 @@
+use rustc_errors::Applicability;
+use rustc_hir::Expr;
+use rustc_lint::LateContext;
+use rustc_middle::ty::{self, Ty, UintTy};
+
+use crate::utils::{snippet_with_applicability, span_lint_and_sugg};
+
+use super::{utils, FN_TO_NUMERIC_CAST};
+
+pub(super) fn check(cx: &LateContext<'_>, expr: &Expr<'_>, cast_expr: &Expr<'_>, cast_from: Ty<'_>, cast_to: Ty<'_>) {
+    // We only want to check casts to `ty::Uint` or `ty::Int`
+    match cast_to.kind() {
+        ty::Uint(_) | ty::Int(..) => { /* continue on */ },
+        _ => return,
+    }
+
+    match cast_from.kind() {
+        ty::FnDef(..) | ty::FnPtr(_) => {
+            let mut applicability = Applicability::MaybeIncorrect;
+            let from_snippet = snippet_with_applicability(cx, cast_expr.span, "x", &mut applicability);
+            let to_nbits = utils::int_ty_to_nbits(cast_to, cx.tcx);
+
+            if (to_nbits >= cx.tcx.data_layout.pointer_size.bits()) && (*cast_to.kind() != ty::Uint(UintTy::Usize)) {
+                span_lint_and_sugg(
+                    cx,
+                    FN_TO_NUMERIC_CAST,
+                    expr.span,
+                    &format!("casting function pointer `{}` to `{}`", from_snippet, cast_to),
+                    "try",
+                    format!("{} as usize", from_snippet),
+                    applicability,
+                );
+            }
+        },
+        _ => {},
+    }
+}
diff --git a/clippy_lints/src/casts/fn_to_numeric_cast_with_truncation.rs b/clippy_lints/src/casts/fn_to_numeric_cast_with_truncation.rs
new file mode 100644
index 00000000000..0085c7b27b2
--- /dev/null
+++ b/clippy_lints/src/casts/fn_to_numeric_cast_with_truncation.rs
@@ -0,0 +1,39 @@
+use rustc_errors::Applicability;
+use rustc_hir::Expr;
+use rustc_lint::LateContext;
+use rustc_middle::ty::{self, Ty};
+
+use crate::utils::{snippet_with_applicability, span_lint_and_sugg};
+
+use super::{utils, FN_TO_NUMERIC_CAST_WITH_TRUNCATION};
+
+pub(super) fn check(cx: &LateContext<'_>, expr: &Expr<'_>, cast_expr: &Expr<'_>, cast_from: Ty<'_>, cast_to: Ty<'_>) {
+    // We only want to check casts to `ty::Uint` or `ty::Int`
+    match cast_to.kind() {
+        ty::Uint(_) | ty::Int(..) => { /* continue on */ },
+        _ => return,
+    }
+    match cast_from.kind() {
+        ty::FnDef(..) | ty::FnPtr(_) => {
+            let mut applicability = Applicability::MaybeIncorrect;
+            let from_snippet = snippet_with_applicability(cx, cast_expr.span, "x", &mut applicability);
+
+            let to_nbits = utils::int_ty_to_nbits(cast_to, cx.tcx);
+            if to_nbits < cx.tcx.data_layout.pointer_size.bits() {
+                span_lint_and_sugg(
+                    cx,
+                    FN_TO_NUMERIC_CAST_WITH_TRUNCATION,
+                    expr.span,
+                    &format!(
+                        "casting function pointer `{}` to `{}`, which truncates the value",
+                        from_snippet, cast_to
+                    ),
+                    "try",
+                    format!("{} as usize", from_snippet),
+                    applicability,
+                );
+            }
+        },
+        _ => {},
+    }
+}
diff --git a/clippy_lints/src/casts/mod.rs b/clippy_lints/src/casts/mod.rs
new file mode 100644
index 00000000000..b726bd75f1d
--- /dev/null
+++ b/clippy_lints/src/casts/mod.rs
@@ -0,0 +1,407 @@
+mod cast_lossless;
+mod cast_possible_truncation;
+mod cast_possible_wrap;
+mod cast_precision_loss;
+mod cast_ptr_alignment;
+mod cast_ref_to_mut;
+mod cast_sign_loss;
+mod char_lit_as_u8;
+mod fn_to_numeric_cast;
+mod fn_to_numeric_cast_with_truncation;
+mod ptr_as_ptr;
+mod unnecessary_cast;
+mod utils;
+
+use rustc_hir::{Expr, ExprKind};
+use rustc_lint::{LateContext, LateLintPass, LintContext};
+use rustc_middle::lint::in_external_macro;
+use rustc_semver::RustcVersion;
+use rustc_session::{declare_tool_lint, impl_lint_pass};
+
+use crate::utils::is_hir_ty_cfg_dependant;
+
+declare_clippy_lint! {
+    /// **What it does:** Checks for casts from any numerical to a float type where
+    /// the receiving type cannot store all values from the original type without
+    /// rounding errors. This possible rounding is to be expected, so this lint is
+    /// `Allow` by default.
+    ///
+    /// Basically, this warns on casting any integer with 32 or more bits to `f32`
+    /// or any 64-bit integer to `f64`.
+    ///
+    /// **Why is this bad?** It's not bad at all. But in some applications it can be
+    /// helpful to know where precision loss can take place. This lint can help find
+    /// those places in the code.
+    ///
+    /// **Known problems:** None.
+    ///
+    /// **Example:**
+    /// ```rust
+    /// let x = u64::MAX;
+    /// x as f64;
+    /// ```
+    pub CAST_PRECISION_LOSS,
+    pedantic,
+    "casts that cause loss of precision, e.g., `x as f32` where `x: u64`"
+}
+
+declare_clippy_lint! {
+    /// **What it does:** Checks for casts from a signed to an unsigned numerical
+    /// type. In this case, negative values wrap around to large positive values,
+    /// which can be quite surprising in practice. However, as the cast works as
+    /// defined, this lint is `Allow` by default.
+    ///
+    /// **Why is this bad?** Possibly surprising results. You can activate this lint
+    /// as a one-time check to see where numerical wrapping can arise.
+    ///
+    /// **Known problems:** None.
+    ///
+    /// **Example:**
+    /// ```rust
+    /// let y: i8 = -1;
+    /// y as u128; // will return 18446744073709551615
+    /// ```
+    pub CAST_SIGN_LOSS,
+    pedantic,
+    "casts from signed types to unsigned types, e.g., `x as u32` where `x: i32`"
+}
+
+declare_clippy_lint! {
+    /// **What it does:** Checks for casts between numerical types that may
+    /// truncate large values. This is expected behavior, so the cast is `Allow` by
+    /// default.
+    ///
+    /// **Why is this bad?** In some problem domains, it is good practice to avoid
+    /// truncation. This lint can be activated to help assess where additional
+    /// checks could be beneficial.
+    ///
+    /// **Known problems:** None.
+    ///
+    /// **Example:**
+    /// ```rust
+    /// fn as_u8(x: u64) -> u8 {
+    ///     x as u8
+    /// }
+    /// ```
+    pub CAST_POSSIBLE_TRUNCATION,
+    pedantic,
+    "casts that may cause truncation of the value, e.g., `x as u8` where `x: u32`, or `x as i32` where `x: f32`"
+}
+
+declare_clippy_lint! {
+    /// **What it does:** Checks for casts from an unsigned type to a signed type of
+    /// the same size. Performing such a cast is a 'no-op' for the compiler,
+    /// i.e., nothing is changed at the bit level, and the binary representation of
+    /// the value is reinterpreted. This can cause wrapping if the value is too big
+    /// for the target signed type. However, the cast works as defined, so this lint
+    /// is `Allow` by default.
+    ///
+    /// **Why is this bad?** While such a cast is not bad in itself, the results can
+    /// be surprising when this is not the intended behavior, as demonstrated by the
+    /// example below.
+    ///
+    /// **Known problems:** None.
+    ///
+    /// **Example:**
+    /// ```rust
+    /// u32::MAX as i32; // will yield a value of `-1`
+    /// ```
+    pub CAST_POSSIBLE_WRAP,
+    pedantic,
+    "casts that may cause wrapping around the value, e.g., `x as i32` where `x: u32` and `x > i32::MAX`"
+}
+
+declare_clippy_lint! {
+    /// **What it does:** Checks for casts between numerical types that may
+    /// be replaced by safe conversion functions.
+    ///
+    /// **Why is this bad?** Rust's `as` keyword will perform many kinds of
+    /// conversions, including silently lossy conversions. Conversion functions such
+    /// as `i32::from` will only perform lossless conversions. Using the conversion
+    /// functions prevents conversions from turning into silent lossy conversions if
+    /// the types of the input expressions ever change, and make it easier for
+    /// people reading the code to know that the conversion is lossless.
+    ///
+    /// **Known problems:** None.
+    ///
+    /// **Example:**
+    /// ```rust
+    /// fn as_u64(x: u8) -> u64 {
+    ///     x as u64
+    /// }
+    /// ```
+    ///
+    /// Using `::from` would look like this:
+    ///
+    /// ```rust
+    /// fn as_u64(x: u8) -> u64 {
+    ///     u64::from(x)
+    /// }
+    /// ```
+    pub CAST_LOSSLESS,
+    pedantic,
+    "casts using `as` that are known to be lossless, e.g., `x as u64` where `x: u8`"
+}
+
+declare_clippy_lint! {
+    /// **What it does:** Checks for casts to the same type, casts of int literals to integer types
+    /// and casts of float literals to float types.
+    ///
+    /// **Why is this bad?** It's just unnecessary.
+    ///
+    /// **Known problems:** None.
+    ///
+    /// **Example:**
+    /// ```rust
+    /// let _ = 2i32 as i32;
+    /// let _ = 0.5 as f32;
+    /// ```
+    ///
+    /// Better:
+    ///
+    /// ```rust
+    /// let _ = 2_i32;
+    /// let _ = 0.5_f32;
+    /// ```
+    pub UNNECESSARY_CAST,
+    complexity,
+    "cast to the same type, e.g., `x as i32` where `x: i32`"
+}
+
+declare_clippy_lint! {
+    /// **What it does:** Checks for casts, using `as` or `pointer::cast`,
+    /// from a less-strictly-aligned pointer to a more-strictly-aligned pointer
+    ///
+    /// **Why is this bad?** Dereferencing the resulting pointer may be undefined
+    /// behavior.
+    ///
+    /// **Known problems:** Using `std::ptr::read_unaligned` and `std::ptr::write_unaligned` or similar
+    /// on the resulting pointer is fine. Is over-zealous: Casts with manual alignment checks or casts like
+    /// u64-> u8 -> u16 can be fine. Miri is able to do a more in-depth analysis.
+    ///
+    /// **Example:**
+    /// ```rust
+    /// let _ = (&1u8 as *const u8) as *const u16;
+    /// let _ = (&mut 1u8 as *mut u8) as *mut u16;
+    ///
+    /// (&1u8 as *const u8).cast::<u16>();
+    /// (&mut 1u8 as *mut u8).cast::<u16>();
+    /// ```
+    pub CAST_PTR_ALIGNMENT,
+    pedantic,
+    "cast from a pointer to a more-strictly-aligned pointer"
+}
+
+declare_clippy_lint! {
+    /// **What it does:** Checks for casts of function pointers to something other than usize
+    ///
+    /// **Why is this bad?**
+    /// Casting a function pointer to anything other than usize/isize is not portable across
+    /// architectures, because you end up losing bits if the target type is too small or end up with a
+    /// bunch of extra bits that waste space and add more instructions to the final binary than
+    /// strictly necessary for the problem
+    ///
+    /// Casting to isize also doesn't make sense since there are no signed addresses.
+    ///
+    /// **Example**
+    ///
+    /// ```rust
+    /// // Bad
+    /// fn fun() -> i32 { 1 }
+    /// let a = fun as i64;
+    ///
+    /// // Good
+    /// fn fun2() -> i32 { 1 }
+    /// let a = fun2 as usize;
+    /// ```
+    pub FN_TO_NUMERIC_CAST,
+    style,
+    "casting a function pointer to a numeric type other than usize"
+}
+
+declare_clippy_lint! {
+    /// **What it does:** Checks for casts of a function pointer to a numeric type not wide enough to
+    /// store address.
+    ///
+    /// **Why is this bad?**
+    /// Such a cast discards some bits of the function's address. If this is intended, it would be more
+    /// clearly expressed by casting to usize first, then casting the usize to the intended type (with
+    /// a comment) to perform the truncation.
+    ///
+    /// **Example**
+    ///
+    /// ```rust
+    /// // Bad
+    /// fn fn1() -> i16 {
+    ///     1
+    /// };
+    /// let _ = fn1 as i32;
+    ///
+    /// // Better: Cast to usize first, then comment with the reason for the truncation
+    /// fn fn2() -> i16 {
+    ///     1
+    /// };
+    /// let fn_ptr = fn2 as usize;
+    /// let fn_ptr_truncated = fn_ptr as i32;
+    /// ```
+    pub FN_TO_NUMERIC_CAST_WITH_TRUNCATION,
+    style,
+    "casting a function pointer to a numeric type not wide enough to store the address"
+}
+
+declare_clippy_lint! {
+    /// **What it does:** Checks for casts of `&T` to `&mut T` anywhere in the code.
+    ///
+    /// **Why is this bad?** It’s basically guaranteed to be undefined behaviour.
+    /// `UnsafeCell` is the only way to obtain aliasable data that is considered
+    /// mutable.
+    ///
+    /// **Known problems:** None.
+    ///
+    /// **Example:**
+    /// ```rust,ignore
+    /// fn x(r: &i32) {
+    ///     unsafe {
+    ///         *(r as *const _ as *mut _) += 1;
+    ///     }
+    /// }
+    /// ```
+    ///
+    /// Instead consider using interior mutability types.
+    ///
+    /// ```rust
+    /// use std::cell::UnsafeCell;
+    ///
+    /// fn x(r: &UnsafeCell<i32>) {
+    ///     unsafe {
+    ///         *r.get() += 1;
+    ///     }
+    /// }
+    /// ```
+    pub CAST_REF_TO_MUT,
+    correctness,
+    "a cast of reference to a mutable pointer"
+}
+
+declare_clippy_lint! {
+    /// **What it does:** Checks for expressions where a character literal is cast
+    /// to `u8` and suggests using a byte literal instead.
+    ///
+    /// **Why is this bad?** In general, casting values to smaller types is
+    /// error-prone and should be avoided where possible. In the particular case of
+    /// converting a character literal to u8, it is easy to avoid by just using a
+    /// byte literal instead. As an added bonus, `b'a'` is even slightly shorter
+    /// than `'a' as u8`.
+    ///
+    /// **Known problems:** None.
+    ///
+    /// **Example:**
+    /// ```rust,ignore
+    /// 'x' as u8
+    /// ```
+    ///
+    /// A better version, using the byte literal:
+    ///
+    /// ```rust,ignore
+    /// b'x'
+    /// ```
+    pub CHAR_LIT_AS_U8,
+    complexity,
+    "casting a character literal to `u8` truncates"
+}
+
+declare_clippy_lint! {
+    /// **What it does:**
+    /// Checks for `as` casts between raw pointers without changing its mutability,
+    /// namely `*const T` to `*const U` and `*mut T` to `*mut U`.
+    ///
+    /// **Why is this bad?**
+    /// Though `as` casts between raw pointers is not terrible, `pointer::cast` is safer because
+    /// it cannot accidentally change the pointer's mutability nor cast the pointer to other types like `usize`.
+    ///
+    /// **Known problems:** None.
+    ///
+    /// **Example:**
+    ///
+    /// ```rust
+    /// let ptr: *const u32 = &42_u32;
+    /// let mut_ptr: *mut u32 = &mut 42_u32;
+    /// let _ = ptr as *const i32;
+    /// let _ = mut_ptr as *mut i32;
+    /// ```
+    /// Use instead:
+    /// ```rust
+    /// let ptr: *const u32 = &42_u32;
+    /// let mut_ptr: *mut u32 = &mut 42_u32;
+    /// let _ = ptr.cast::<i32>();
+    /// let _ = mut_ptr.cast::<i32>();
+    /// ```
+    pub PTR_AS_PTR,
+    pedantic,
+    "casting using `as` from and to raw pointers that doesn't change its mutability, where `pointer::cast` could take the place of `as`"
+}
+
+pub struct Casts {
+    msrv: Option<RustcVersion>,
+}
+
+impl Casts {
+    #[must_use]
+    pub fn new(msrv: Option<RustcVersion>) -> Self {
+        Self { msrv }
+    }
+}
+
+impl_lint_pass!(Casts => [
+    CAST_PRECISION_LOSS,
+    CAST_SIGN_LOSS,
+    CAST_POSSIBLE_TRUNCATION,
+    CAST_POSSIBLE_WRAP,
+    CAST_LOSSLESS,
+    CAST_REF_TO_MUT,
+    CAST_PTR_ALIGNMENT,
+    UNNECESSARY_CAST,
+    FN_TO_NUMERIC_CAST,
+    FN_TO_NUMERIC_CAST_WITH_TRUNCATION,
+    CHAR_LIT_AS_U8,
+    PTR_AS_PTR,
+]);
+
+impl<'tcx> LateLintPass<'tcx> for Casts {
+    fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
+        if expr.span.from_expansion() {
+            return;
+        }
+
+        if let ExprKind::Cast(ref cast_expr, cast_to) = expr.kind {
+            if is_hir_ty_cfg_dependant(cx, cast_to) {
+                return;
+            }
+            let (cast_from, cast_to) = (
+                cx.typeck_results().expr_ty(cast_expr),
+                cx.typeck_results().expr_ty(expr),
+            );
+
+            if unnecessary_cast::check(cx, expr, cast_expr, cast_from, cast_to) {
+                return;
+            }
+
+            fn_to_numeric_cast::check(cx, expr, cast_expr, cast_from, cast_to);
+            fn_to_numeric_cast_with_truncation::check(cx, expr, cast_expr, cast_from, cast_to);
+            if cast_from.is_numeric() && cast_to.is_numeric() && !in_external_macro(cx.sess(), expr.span) {
+                cast_possible_truncation::check(cx, expr, cast_from, cast_to);
+                cast_possible_wrap::check(cx, expr, cast_from, cast_to);
+                cast_precision_loss::check(cx, expr, cast_from, cast_to);
+                cast_lossless::check(cx, expr, cast_expr, cast_from, cast_to);
+                cast_sign_loss::check(cx, expr, cast_expr, cast_from, cast_to);
+            }
+        }
+
+        cast_ref_to_mut::check(cx, expr);
+        cast_ptr_alignment::check(cx, expr);
+        char_lit_as_u8::check(cx, expr);
+        ptr_as_ptr::check(cx, expr, &self.msrv);
+    }
+
+    extract_msrv_attr!(LateContext);
+}
diff --git a/clippy_lints/src/casts/ptr_as_ptr.rs b/clippy_lints/src/casts/ptr_as_ptr.rs
new file mode 100644
index 00000000000..abfbadf3642
--- /dev/null
+++ b/clippy_lints/src/casts/ptr_as_ptr.rs
@@ -0,0 +1,52 @@
+use std::borrow::Cow;
+
+use rustc_errors::Applicability;
+use rustc_hir::{Expr, ExprKind, Mutability, TyKind};
+use rustc_lint::LateContext;
+use rustc_middle::ty::{self, TypeAndMut};
+use rustc_semver::RustcVersion;
+
+use if_chain::if_chain;
+
+use crate::utils::sugg::Sugg;
+use crate::utils::{meets_msrv, span_lint_and_sugg};
+
+use super::PTR_AS_PTR;
+
+const PTR_AS_PTR_MSRV: RustcVersion = RustcVersion::new(1, 38, 0);
+
+pub(super) fn check(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>, msrv: &Option<RustcVersion>) {
+    if !meets_msrv(msrv.as_ref(), &PTR_AS_PTR_MSRV) {
+        return;
+    }
+
+    if_chain! {
+        if let ExprKind::Cast(cast_expr, cast_to_hir_ty) = expr.kind;
+        let (cast_from, cast_to) = (cx.typeck_results().expr_ty(cast_expr), cx.typeck_results().expr_ty(expr));
+        if let ty::RawPtr(TypeAndMut { mutbl: from_mutbl, .. }) = cast_from.kind();
+        if let ty::RawPtr(TypeAndMut { ty: to_pointee_ty, mutbl: to_mutbl }) = cast_to.kind();
+        if matches!((from_mutbl, to_mutbl),
+            (Mutability::Not, Mutability::Not) | (Mutability::Mut, Mutability::Mut));
+        // The `U` in `pointer::cast` have to be `Sized`
+        // as explained here: https://github.com/rust-lang/rust/issues/60602.
+        if to_pointee_ty.is_sized(cx.tcx.at(expr.span), cx.param_env);
+        then {
+            let mut applicability = Applicability::MachineApplicable;
+            let cast_expr_sugg = Sugg::hir_with_applicability(cx, cast_expr, "_", &mut applicability);
+            let turbofish = match &cast_to_hir_ty.kind {
+                    TyKind::Infer => Cow::Borrowed(""),
+                    TyKind::Ptr(mut_ty) if matches!(mut_ty.ty.kind, TyKind::Infer) => Cow::Borrowed(""),
+                    _ => Cow::Owned(format!("::<{}>", to_pointee_ty)),
+                };
+            span_lint_and_sugg(
+                cx,
+                PTR_AS_PTR,
+                expr.span,
+                "`as` casting between raw pointers without changing its mutability",
+                "try `pointer::cast`, a safer alternative",
+                format!("{}.cast{}()", cast_expr_sugg.maybe_par(), turbofish),
+                applicability,
+            );
+        }
+    }
+}
diff --git a/clippy_lints/src/casts/unnecessary_cast.rs b/clippy_lints/src/casts/unnecessary_cast.rs
new file mode 100644
index 00000000000..fa2a07ef1da
--- /dev/null
+++ b/clippy_lints/src/casts/unnecessary_cast.rs
@@ -0,0 +1,106 @@
+use rustc_ast::{LitFloatType, LitIntType, LitKind};
+use rustc_errors::Applicability;
+use rustc_hir::{Expr, ExprKind, Lit, UnOp};
+use rustc_lint::{LateContext, LintContext};
+use rustc_middle::lint::in_external_macro;
+use rustc_middle::ty::{self, FloatTy, InferTy, Ty};
+
+use if_chain::if_chain;
+
+use crate::utils::{numeric_literal::NumericLiteral, snippet_opt, span_lint, span_lint_and_sugg};
+
+use super::UNNECESSARY_CAST;
+
+pub(super) fn check(
+    cx: &LateContext<'_>,
+    expr: &Expr<'_>,
+    cast_expr: &Expr<'_>,
+    cast_from: Ty<'_>,
+    cast_to: Ty<'_>,
+) -> bool {
+    if let Some(lit) = get_numeric_literal(cast_expr) {
+        let literal_str = snippet_opt(cx, cast_expr.span).unwrap_or_default();
+
+        if_chain! {
+            if let LitKind::Int(n, _) = lit.node;
+            if let Some(src) = snippet_opt(cx, lit.span);
+            if cast_to.is_floating_point();
+            if let Some(num_lit) = NumericLiteral::from_lit_kind(&src, &lit.node);
+            let from_nbits = 128 - n.leading_zeros();
+            let to_nbits = fp_ty_mantissa_nbits(cast_to);
+            if from_nbits != 0 && to_nbits != 0 && from_nbits <= to_nbits && num_lit.is_decimal();
+            then {
+                let literal_str = if is_unary_neg(cast_expr) { format!("-{}", num_lit.integer) } else { num_lit.integer.into() };
+                lint_unnecessary_cast(cx, expr, &literal_str, cast_from, cast_to);
+                return true
+            }
+        }
+
+        match lit.node {
+            LitKind::Int(_, LitIntType::Unsuffixed) if cast_to.is_integral() => {
+                lint_unnecessary_cast(cx, expr, &literal_str, cast_from, cast_to);
+            },
+            LitKind::Float(_, LitFloatType::Unsuffixed) if cast_to.is_floating_point() => {
+                lint_unnecessary_cast(cx, expr, &literal_str, cast_from, cast_to);
+            },
+            LitKind::Int(_, LitIntType::Unsuffixed) | LitKind::Float(_, LitFloatType::Unsuffixed) => {},
+            _ => {
+                if cast_from.kind() == cast_to.kind() && !in_external_macro(cx.sess(), expr.span) {
+                    span_lint(
+                        cx,
+                        UNNECESSARY_CAST,
+                        expr.span,
+                        &format!(
+                            "casting to the same type is unnecessary (`{}` -> `{}`)",
+                            cast_from, cast_to
+                        ),
+                    );
+                    return true;
+                }
+            },
+        }
+    }
+
+    false
+}
+
+fn lint_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(
+        cx,
+        UNNECESSARY_CAST,
+        expr.span,
+        &format!("casting {} literal to `{}` is unnecessary", literal_kind_name, cast_to),
+        "try",
+        format!("{}_{}", literal_str.trim_end_matches('.'), cast_to),
+        Applicability::MachineApplicable,
+    );
+}
+
+fn get_numeric_literal<'e>(expr: &'e Expr<'e>) -> Option<&'e Lit> {
+    match expr.kind {
+        ExprKind::Lit(ref lit) => Some(lit),
+        ExprKind::Unary(UnOp::Neg, e) => {
+            if let ExprKind::Lit(ref lit) = e.kind {
+                Some(lit)
+            } else {
+                None
+            }
+        },
+        _ => None,
+    }
+}
+
+/// Returns the mantissa bits wide of a fp type.
+/// Will return 0 if the type is not a fp
+fn fp_ty_mantissa_nbits(typ: Ty<'_>) -> u32 {
+    match typ.kind() {
+        ty::Float(FloatTy::F32) => 23,
+        ty::Float(FloatTy::F64) | ty::Infer(InferTy::FloatVar(_)) => 52,
+        _ => 0,
+    }
+}
+
+fn is_unary_neg(expr: &Expr<'_>) -> bool {
+    matches!(expr.kind, ExprKind::Unary(UnOp::Neg, _))
+}
diff --git a/clippy_lints/src/casts/utils.rs b/clippy_lints/src/casts/utils.rs
new file mode 100644
index 00000000000..00fd0b3473b
--- /dev/null
+++ b/clippy_lints/src/casts/utils.rs
@@ -0,0 +1,25 @@
+use rustc_middle::ty::{self, IntTy, Ty, TyCtxt, UintTy};
+
+/// Returns the size in bits of an integral type.
+/// Will return 0 if the type is not an int or uint variant
+pub(super) fn int_ty_to_nbits(typ: Ty<'_>, tcx: TyCtxt<'_>) -> u64 {
+    match typ.kind() {
+        ty::Int(i) => match i {
+            IntTy::Isize => tcx.data_layout.pointer_size.bits(),
+            IntTy::I8 => 8,
+            IntTy::I16 => 16,
+            IntTy::I32 => 32,
+            IntTy::I64 => 64,
+            IntTy::I128 => 128,
+        },
+        ty::Uint(i) => match i {
+            UintTy::Usize => tcx.data_layout.pointer_size.bits(),
+            UintTy::U8 => 8,
+            UintTy::U16 => 16,
+            UintTy::U32 => 32,
+            UintTy::U64 => 64,
+            UintTy::U128 => 128,
+        },
+        _ => 0,
+    }
+}