diff --git a/CHANGELOG.md b/CHANGELOG.md
index 2373cb87eed..c9bea1e8ef5 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -689,6 +689,7 @@ All notable changes to this project will be documented in this file.
[`float_cmp`]: https://rust-lang-nursery.github.io/rust-clippy/master/index.html#float_cmp
[`float_cmp_const`]: https://rust-lang-nursery.github.io/rust-clippy/master/index.html#float_cmp_const
[`fn_to_numeric_cast`]: https://rust-lang-nursery.github.io/rust-clippy/master/index.html#fn_to_numeric_cast
+[`fn_to_numeric_cast_with_truncation`]: https://rust-lang-nursery.github.io/rust-clippy/master/index.html#fn_to_numeric_cast_with_truncation
[`for_kv_map`]: https://rust-lang-nursery.github.io/rust-clippy/master/index.html#for_kv_map
[`for_loop_over_option`]: https://rust-lang-nursery.github.io/rust-clippy/master/index.html#for_loop_over_option
[`for_loop_over_result`]: https://rust-lang-nursery.github.io/rust-clippy/master/index.html#for_loop_over_result
diff --git a/README.md b/README.md
index f332a3f645d..40ece34c6fa 100644
--- a/README.md
+++ b/README.md
@@ -9,7 +9,7 @@ We are currently in the process of discussing Clippy 1.0 via the RFC process in
A collection of lints to catch common mistakes and improve your [Rust](https://github.com/rust-lang/rust) code.
-[There are 278 lints included in this crate!](https://rust-lang-nursery.github.io/rust-clippy/master/index.html)
+[There are 279 lints included in this crate!](https://rust-lang-nursery.github.io/rust-clippy/master/index.html)
We have a bunch of lint categories to allow you to choose how much Clippy is supposed to ~~annoy~~ help you:
diff --git a/clippy_lints/src/lib.rs b/clippy_lints/src/lib.rs
index b181a4c17ca..3779b09ecf3 100644
--- a/clippy_lints/src/lib.rs
+++ b/clippy_lints/src/lib.rs
@@ -698,6 +698,7 @@ pub fn register_plugins(reg: &mut rustc_plugin::Registry<'_>, conf: &Conf) {
types::CAST_PTR_ALIGNMENT,
types::CHAR_LIT_AS_U8,
types::FN_TO_NUMERIC_CAST,
+ types::FN_TO_NUMERIC_CAST_WITH_TRUNCATION,
types::IMPLICIT_HASHER,
types::LET_UNIT_VALUE,
types::OPTION_OPTION,
@@ -791,6 +792,7 @@ pub fn register_plugins(reg: &mut rustc_plugin::Registry<'_>, conf: &Conf) {
returns::NEEDLESS_RETURN,
strings::STRING_LIT_AS_BYTES,
types::FN_TO_NUMERIC_CAST,
+ types::FN_TO_NUMERIC_CAST_WITH_TRUNCATION,
types::IMPLICIT_HASHER,
types::LET_UNIT_VALUE,
unsafe_removed_from_name::UNSAFE_REMOVED_FROM_NAME,
diff --git a/clippy_lints/src/types.rs b/clippy_lints/src/types.rs
index f39a26db509..d3aa8de825b 100644
--- a/clippy_lints/src/types.rs
+++ b/clippy_lints/src/types.rs
@@ -746,6 +746,32 @@ declare_clippy_lint! {
"casting a function pointer to a numeric type other than usize"
}
+/// **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;
+/// ```
+declare_clippy_lint! {
+ pub FN_TO_NUMERIC_CAST_WITH_TRUNCATION,
+ style,
+ "casting a function pointer to a numeric type not wide enough to store the address"
+}
+
/// Returns the size in bits of an integral type.
/// Will return 0 if the type is not an int or uint variant
fn int_ty_to_nbits(typ: Ty<'_>, tcx: TyCtxt<'_, '_, '_>) -> u64 {
@@ -1054,7 +1080,19 @@ fn lint_fn_to_numeric_cast(cx: &LateContext<'_, '_>, expr: &Expr, cast_expr: &Ex
match cast_from.sty {
ty::FnDef(..) | ty::FnPtr(_) => {
let from_snippet = snippet(cx, cast_expr.span, "x");
- if cast_to.sty != ty::Uint(UintTy::Usize) {
+
+ let to_nbits = 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)
+ );
+
+ } else if cast_to.sty != ty::Uint(UintTy::Usize) {
span_lint_and_sugg(
cx,
FN_TO_NUMERIC_CAST,
diff --git a/tests/ui/fn_to_numeric_cast.rs b/tests/ui/fn_to_numeric_cast.rs
index d250af61847..6d0fd3d8ab8 100644
--- a/tests/ui/fn_to_numeric_cast.rs
+++ b/tests/ui/fn_to_numeric_cast.rs
@@ -1,6 +1,6 @@
#![feature(tool_lints)]
-#[warn(clippy::fn_to_numeric_cast)]
+#![warn(clippy::fn_to_numeric_cast)]
fn foo() -> String { String::new() }
diff --git a/tests/ui/fn_to_numeric_cast.stderr b/tests/ui/fn_to_numeric_cast.stderr
new file mode 100644
index 00000000000..be8bc9058b4
--- /dev/null
+++ b/tests/ui/fn_to_numeric_cast.stderr
@@ -0,0 +1,142 @@
+error: casting function pointer `foo` to `i8`
+ --> $DIR/fn_to_numeric_cast.rs:8:13
+ |
+8 | let _ = foo as i8;
+ | ^^^^^^^^^ help: try: `foo as usize`
+ |
+ = note: `-D clippy::fn-to-numeric-cast` implied by `-D warnings`
+
+error: casting function pointer `foo` to `i16`
+ --> $DIR/fn_to_numeric_cast.rs:9:13
+ |
+9 | let _ = foo as i16;
+ | ^^^^^^^^^^ help: try: `foo as usize`
+
+error: casting function pointer `foo` to `i32`
+ --> $DIR/fn_to_numeric_cast.rs:10:13
+ |
+10 | let _ = foo as i32;
+ | ^^^^^^^^^^ help: try: `foo as usize`
+
+error: casting function pointer `foo` to `i64`
+ --> $DIR/fn_to_numeric_cast.rs:11:13
+ |
+11 | let _ = foo as i64;
+ | ^^^^^^^^^^ help: try: `foo as usize`
+
+error: casting function pointer `foo` to `i128`
+ --> $DIR/fn_to_numeric_cast.rs:12:13
+ |
+12 | let _ = foo as i128;
+ | ^^^^^^^^^^^ help: try: `foo as usize`
+
+error: casting function pointer `foo` to `isize`
+ --> $DIR/fn_to_numeric_cast.rs:13:13
+ |
+13 | let _ = foo as isize;
+ | ^^^^^^^^^^^^ help: try: `foo as usize`
+
+error: casting function pointer `foo` to `u8`
+ --> $DIR/fn_to_numeric_cast.rs:15:13
+ |
+15 | let _ = foo as u8;
+ | ^^^^^^^^^ help: try: `foo as usize`
+
+error: casting function pointer `foo` to `u16`
+ --> $DIR/fn_to_numeric_cast.rs:16:13
+ |
+16 | let _ = foo as u16;
+ | ^^^^^^^^^^ help: try: `foo as usize`
+
+error: casting function pointer `foo` to `u32`
+ --> $DIR/fn_to_numeric_cast.rs:17:13
+ |
+17 | let _ = foo as u32;
+ | ^^^^^^^^^^ help: try: `foo as usize`
+
+error: casting function pointer `foo` to `u64`
+ --> $DIR/fn_to_numeric_cast.rs:18:13
+ |
+18 | let _ = foo as u64;
+ | ^^^^^^^^^^ help: try: `foo as usize`
+
+error: casting function pointer `foo` to `u128`
+ --> $DIR/fn_to_numeric_cast.rs:19:13
+ |
+19 | let _ = foo as u128;
+ | ^^^^^^^^^^^ help: try: `foo as usize`
+
+error: casting function pointer `abc` to `i8`
+ --> $DIR/fn_to_numeric_cast.rs:28:13
+ |
+28 | let _ = abc as i8;
+ | ^^^^^^^^^ help: try: `abc as usize`
+
+error: casting function pointer `abc` to `i16`
+ --> $DIR/fn_to_numeric_cast.rs:29:13
+ |
+29 | let _ = abc as i16;
+ | ^^^^^^^^^^ help: try: `abc as usize`
+
+error: casting function pointer `abc` to `i32`
+ --> $DIR/fn_to_numeric_cast.rs:30:13
+ |
+30 | let _ = abc as i32;
+ | ^^^^^^^^^^ help: try: `abc as usize`
+
+error: casting function pointer `abc` to `i64`
+ --> $DIR/fn_to_numeric_cast.rs:31:13
+ |
+31 | let _ = abc as i64;
+ | ^^^^^^^^^^ help: try: `abc as usize`
+
+error: casting function pointer `abc` to `i128`
+ --> $DIR/fn_to_numeric_cast.rs:32:13
+ |
+32 | let _ = abc as i128;
+ | ^^^^^^^^^^^ help: try: `abc as usize`
+
+error: casting function pointer `abc` to `isize`
+ --> $DIR/fn_to_numeric_cast.rs:33:13
+ |
+33 | let _ = abc as isize;
+ | ^^^^^^^^^^^^ help: try: `abc as usize`
+
+error: casting function pointer `abc` to `u8`
+ --> $DIR/fn_to_numeric_cast.rs:35:13
+ |
+35 | let _ = abc as u8;
+ | ^^^^^^^^^ help: try: `abc as usize`
+
+error: casting function pointer `abc` to `u16`
+ --> $DIR/fn_to_numeric_cast.rs:36:13
+ |
+36 | let _ = abc as u16;
+ | ^^^^^^^^^^ help: try: `abc as usize`
+
+error: casting function pointer `abc` to `u32`
+ --> $DIR/fn_to_numeric_cast.rs:37:13
+ |
+37 | let _ = abc as u32;
+ | ^^^^^^^^^^ help: try: `abc as usize`
+
+error: casting function pointer `abc` to `u64`
+ --> $DIR/fn_to_numeric_cast.rs:38:13
+ |
+38 | let _ = abc as u64;
+ | ^^^^^^^^^^ help: try: `abc as usize`
+
+error: casting function pointer `abc` to `u128`
+ --> $DIR/fn_to_numeric_cast.rs:39:13
+ |
+39 | let _ = abc as u128;
+ | ^^^^^^^^^^^ help: try: `abc as usize`
+
+error: casting function pointer `f` to `i32`
+ --> $DIR/fn_to_numeric_cast.rs:46:5
+ |
+46 | f as i32
+ | ^^^^^^^^ help: try: `f as usize`
+
+error: aborting due to 23 previous errors
+
diff --git a/tests/ui/fn_to_numeric_cast_with_truncation.rs b/tests/ui/fn_to_numeric_cast_with_truncation.rs
new file mode 100644
index 00000000000..82bbaec201f
--- /dev/null
+++ b/tests/ui/fn_to_numeric_cast_with_truncation.rs
@@ -0,0 +1,23 @@
+#![feature(tool_lints)]
+
+#![warn(clippy::fn_to_numeric_cast_with_truncation)]
+#![allow(clippy::fn_to_numeric_cast)]
+
+fn foo() -> String { String::new() }
+
+fn test_fn_to_numeric_cast_with_truncation() {
+ let _ = foo as i8;
+ let _ = foo as i16;
+ let _ = foo as i32;
+ let _ = foo as u8;
+ let _ = foo as u16;
+ let _ = foo as u32;
+
+ // TODO: Is it bad to have these tests?
+ // Running the tests on a different architechture will
+ // produce different results
+ let _ = foo as u64;
+ let _ = foo as i64;
+}
+
+fn main() {}
diff --git a/tests/ui/fn_to_numeric_cast_with_truncation.stderr b/tests/ui/fn_to_numeric_cast_with_truncation.stderr
new file mode 100644
index 00000000000..cae4b6fbd40
--- /dev/null
+++ b/tests/ui/fn_to_numeric_cast_with_truncation.stderr
@@ -0,0 +1,40 @@
+error: casting function pointer `foo` to `i8`, which truncates the value
+ --> $DIR/fn_to_numeric_cast_with_truncation.rs:9:13
+ |
+9 | let _ = foo as i8;
+ | ^^^^^^^^^ help: try: `foo as usize`
+ |
+ = note: `-D clippy::fn-to-numeric-cast-with-truncation` implied by `-D warnings`
+
+error: casting function pointer `foo` to `i16`, which truncates the value
+ --> $DIR/fn_to_numeric_cast_with_truncation.rs:10:13
+ |
+10 | let _ = foo as i16;
+ | ^^^^^^^^^^ help: try: `foo as usize`
+
+error: casting function pointer `foo` to `i32`, which truncates the value
+ --> $DIR/fn_to_numeric_cast_with_truncation.rs:11:13
+ |
+11 | let _ = foo as i32;
+ | ^^^^^^^^^^ help: try: `foo as usize`
+
+error: casting function pointer `foo` to `u8`, which truncates the value
+ --> $DIR/fn_to_numeric_cast_with_truncation.rs:12:13
+ |
+12 | let _ = foo as u8;
+ | ^^^^^^^^^ help: try: `foo as usize`
+
+error: casting function pointer `foo` to `u16`, which truncates the value
+ --> $DIR/fn_to_numeric_cast_with_truncation.rs:13:13
+ |
+13 | let _ = foo as u16;
+ | ^^^^^^^^^^ help: try: `foo as usize`
+
+error: casting function pointer `foo` to `u32`, which truncates the value
+ --> $DIR/fn_to_numeric_cast_with_truncation.rs:14:13
+ |
+14 | let _ = foo as u32;
+ | ^^^^^^^^^^ help: try: `foo as usize`
+
+error: aborting due to 6 previous errors
+