Ignore more type aliases in unnecessary_cast

clippy_lints/src/casts/unnecessary_cast.rs

@@ -1,15 +1,17 @@
 use clippy_utils::diagnostics::span_lint_and_sugg;
 use clippy_utils::numeric_literal::NumericLiteral;
 use clippy_utils::source::snippet_opt;
-use clippy_utils::{get_parent_expr, is_hir_ty_cfg_dependant, is_ty_alias, path_to_local};
+use clippy_utils::visitors::{for_each_expr, Visitable};
+use clippy_utils::{get_parent_expr, get_parent_node, is_hir_ty_cfg_dependant, is_ty_alias, path_to_local};
 use if_chain::if_chain;
 use rustc_ast::{LitFloatType, LitIntType, LitKind};
 use rustc_errors::Applicability;
-use rustc_hir::def::Res;
+use rustc_hir::def::{DefKind, Res};
 use rustc_hir::{Expr, ExprKind, Lit, Node, Path, QPath, TyKind, UnOp};
 use rustc_lint::{LateContext, LintContext};
 use rustc_middle::lint::in_external_macro;
 use rustc_middle::ty::{self, FloatTy, InferTy, Ty};
+use std::ops::ControlFlow;
 
 use super::UNNECESSARY_CAST;
 
@@ -59,7 +61,7 @@ pub(super) fn check<'tcx>(
         }
     }
 
-    // skip cast of local to type alias
+    // skip cast of local that is a type alias
     if let ExprKind::Cast(inner, ..) = expr.kind
         && let ExprKind::Path(qpath) = inner.kind
         && let QPath::Resolved(None, Path { res, .. }) = qpath
@@ -83,6 +85,11 @@ pub(super) fn check<'tcx>(
         }
     }
 
+    // skip cast of fn call that returns type alias
+    if let ExprKind::Cast(inner, ..) = expr.kind && is_cast_from_ty_alias(cx, inner, cast_from) {
+        return false;
+    }
+
     // skip cast to non-primitive type
     if_chain! {
         if let ExprKind::Cast(_, cast_to) = expr.kind;
@@ -223,3 +230,61 @@ fn fp_ty_mantissa_nbits(typ: Ty<'_>) -> u32 {
         _ => 0,
     }
 }
+
+/// Finds whether an `Expr` returns a type alias.
+///
+/// TODO: Maybe we should move this to `clippy_utils` so others won't need to go down this dark,
+/// dark path reimplementing this (or something similar).
+fn is_cast_from_ty_alias<'tcx>(cx: &LateContext<'tcx>, expr: impl Visitable<'tcx>, cast_from: Ty<'tcx>) -> bool {
+    for_each_expr(expr, |expr| {
+        // Calls are a `Path`, and usage of locals are a `Path`. So, this checks
+        // - call() as i32
+        // - local as i32
+        if let ExprKind::Path(qpath) = expr.kind {
+            let res = cx.qpath_res(&qpath, expr.hir_id);
+            // Function call
+            if let Res::Def(DefKind::Fn, def_id) = res {
+                let Some(snippet) = snippet_opt(cx, cx.tcx.def_span(def_id)) else {
+                    return ControlFlow::Continue(());
+                };
+                // This is the worst part of this entire function. This is the only way I know of to
+                // check whether a function returns a type alias. Sure, you can get the return type
+                // from a function in the current crate as an hir ty, but how do you get it for
+                // external functions?? Simple: It's impossible. So, we check whether a part of the
+                // function's declaration snippet is exactly equal to the `Ty`. That way, we can
+                // see whether it's a type alias.
+                //
+                // Will this work for more complex types? Probably not!
+                if !snippet
+                    .split("->")
+                    .skip(0)
+                    .map(|s| {
+                        s.trim() == cast_from.to_string()
+                            || s.split("where").any(|ty| ty.trim() == cast_from.to_string())
+                    })
+                    .any(|a| a)
+                {
+                    return ControlFlow::Break(());
+                }
+            // Local usage
+            } else if let Res::Local(hir_id) = res
+                && let Some(parent) = get_parent_node(cx.tcx, hir_id)
+                && let Node::Local(l) = parent
+            {
+                if let Some(e) = l.init && is_cast_from_ty_alias(cx, e, cast_from) {
+                    return ControlFlow::Break::<()>(());
+                }
+
+                if let Some(ty) = l.ty
+                    && let TyKind::Path(qpath) = ty.kind
+                    && is_ty_alias(&qpath)
+                {
+                    return ControlFlow::Break::<()>(());
+                }
+            }
+        }
+
+        ControlFlow::Continue(())
+    })
+    .is_some()
+}

tests/ui/auxiliary/extern_fake_libc.rs

@@ -0,0 +1,10 @@
+#![allow(nonstandard_style)]
+#![allow(clippy::missing_safety_doc, unused)]
+
+type pid_t = i32;
+pub unsafe fn getpid() -> pid_t {
+    pid_t::from(0)
+}
+pub fn getpid_SAFE_TRUTH() -> pid_t {
+    unsafe { getpid() }
+}

tests/ui/unnecessary_cast.fixed

@@ -1,13 +1,17 @@
 //@run-rustfix
+//@aux-build:extern_fake_libc.rs
 #![warn(clippy::unnecessary_cast)]
 #![allow(
-    unused,
     clippy::borrow_as_ptr,
     clippy::no_effect,
     clippy::nonstandard_macro_braces,
-    clippy::unnecessary_operation
+    clippy::unnecessary_operation,
+    nonstandard_style,
+    unused
 )]
 
+extern crate extern_fake_libc;
+
 type PtrConstU8 = *const u8;
 type PtrMutU8 = *mut u8;
 
@@ -19,6 +23,21 @@ fn uwu<T, U>(ptr: *const T) -> *const U {
     ptr as *const U
 }
 
+mod fake_libc {
+    type pid_t = i32;
+    pub unsafe fn getpid() -> pid_t {
+        pid_t::from(0)
+    }
+    // Make sure a where clause does not break it
+    pub fn getpid_SAFE_TRUTH<T: Clone>(t: &T) -> pid_t
+    where
+        T: Clone,
+    {
+        t;
+        unsafe { getpid() }
+    }
+}
+
 #[rustfmt::skip]
 fn main() {
     // Test cast_unnecessary
@@ -82,6 +101,10 @@ fn main() {
     // or from
     let x: I32Alias = 1;
     let y = x as u64;
+    fake_libc::getpid_SAFE_TRUTH(&0u32) as i32;
+    extern_fake_libc::getpid_SAFE_TRUTH() as i32;
+    let pid = unsafe { fake_libc::getpid() };
+    pid as i32;
 
     let i8_ptr: *const i8 = &1;
     let u8_ptr: *const u8 = &1;

tests/ui/unnecessary_cast.rs

@@ -1,13 +1,17 @@
 //@run-rustfix
+//@aux-build:extern_fake_libc.rs
 #![warn(clippy::unnecessary_cast)]
 #![allow(
-    unused,
     clippy::borrow_as_ptr,
     clippy::no_effect,
     clippy::nonstandard_macro_braces,
-    clippy::unnecessary_operation
+    clippy::unnecessary_operation,
+    nonstandard_style,
+    unused
 )]
 
+extern crate extern_fake_libc;
+
 type PtrConstU8 = *const u8;
 type PtrMutU8 = *mut u8;
 
@@ -19,6 +23,21 @@ fn uwu<T, U>(ptr: *const T) -> *const U {
     ptr as *const U
 }
 
+mod fake_libc {
+    type pid_t = i32;
+    pub unsafe fn getpid() -> pid_t {
+        pid_t::from(0)
+    }
+    // Make sure a where clause does not break it
+    pub fn getpid_SAFE_TRUTH<T: Clone>(t: &T) -> pid_t
+    where
+        T: Clone,
+    {
+        t;
+        unsafe { getpid() }
+    }
+}
+
 #[rustfmt::skip]
 fn main() {
     // Test cast_unnecessary
@@ -82,6 +101,10 @@ fn main() {
     // or from
     let x: I32Alias = 1;
     let y = x as u64;
+    fake_libc::getpid_SAFE_TRUTH(&0u32) as i32;
+    extern_fake_libc::getpid_SAFE_TRUTH() as i32;
+    let pid = unsafe { fake_libc::getpid() };
+    pid as i32;
 
     let i8_ptr: *const i8 = &1;
     let u8_ptr: *const u8 = &1;

tests/ui/unnecessary_cast.stderr

@@ -1,5 +1,5 @@
 error: casting raw pointers to the same type and constness is unnecessary (`*const T` -> `*const T`)
-  --> $DIR/unnecessary_cast.rs:15:5
+  --> $DIR/unnecessary_cast.rs:19:5
    |
 LL |     ptr as *const T
    |     ^^^^^^^^^^^^^^^ help: try: `ptr`
@@ -7,223 +7,223 @@ LL |     ptr as *const T
    = note: `-D clippy::unnecessary-cast` implied by `-D warnings`
 
 error: casting integer literal to `i32` is unnecessary
-  --> $DIR/unnecessary_cast.rs:25:5
+  --> $DIR/unnecessary_cast.rs:44:5
    |
 LL |     1i32 as i32;
    |     ^^^^^^^^^^^ help: try: `1_i32`
 
 error: casting float literal to `f32` is unnecessary
-  --> $DIR/unnecessary_cast.rs:26:5
+  --> $DIR/unnecessary_cast.rs:45:5
    |
 LL |     1f32 as f32;
    |     ^^^^^^^^^^^ help: try: `1_f32`
 
 error: casting to the same type is unnecessary (`bool` -> `bool`)
-  --> $DIR/unnecessary_cast.rs:27:5
+  --> $DIR/unnecessary_cast.rs:46:5
    |
 LL |     false as bool;
    |     ^^^^^^^^^^^^^ help: try: `false`
 
 error: casting integer literal to `i32` is unnecessary
-  --> $DIR/unnecessary_cast.rs:30:5
+  --> $DIR/unnecessary_cast.rs:49:5
    |
 LL |     -1_i32 as i32;
    |     ^^^^^^^^^^^^^ help: try: `-1_i32`
 
 error: casting integer literal to `i32` is unnecessary
-  --> $DIR/unnecessary_cast.rs:31:5
+  --> $DIR/unnecessary_cast.rs:50:5
    |
 LL |     - 1_i32 as i32;
    |     ^^^^^^^^^^^^^^ help: try: `- 1_i32`
 
 error: casting float literal to `f32` is unnecessary
-  --> $DIR/unnecessary_cast.rs:32:5
+  --> $DIR/unnecessary_cast.rs:51:5
    |
 LL |     -1f32 as f32;
    |     ^^^^^^^^^^^^ help: try: `-1_f32`
 
 error: casting integer literal to `i32` is unnecessary
-  --> $DIR/unnecessary_cast.rs:33:5
+  --> $DIR/unnecessary_cast.rs:52:5
    |
 LL |     1_i32 as i32;
    |     ^^^^^^^^^^^^ help: try: `1_i32`
 
 error: casting float literal to `f32` is unnecessary
-  --> $DIR/unnecessary_cast.rs:34:5
+  --> $DIR/unnecessary_cast.rs:53:5
    |
 LL |     1_f32 as f32;
    |     ^^^^^^^^^^^^ help: try: `1_f32`
 
 error: casting raw pointers to the same type and constness is unnecessary (`*const u8` -> `*const u8`)
-  --> $DIR/unnecessary_cast.rs:36:22
+  --> $DIR/unnecessary_cast.rs:55:22
    |
 LL |     let _: *mut u8 = [1u8, 2].as_ptr() as *const u8 as *mut u8;
    |                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `[1u8, 2].as_ptr()`
 
 error: casting raw pointers to the same type and constness is unnecessary (`*const u8` -> `*const u8`)
-  --> $DIR/unnecessary_cast.rs:38:5
+  --> $DIR/unnecessary_cast.rs:57:5
    |
 LL |     [1u8, 2].as_ptr() as *const u8;
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `[1u8, 2].as_ptr()`
 
 error: casting raw pointers to the same type and constness is unnecessary (`*mut u8` -> `*mut u8`)
-  --> $DIR/unnecessary_cast.rs:40:5
+  --> $DIR/unnecessary_cast.rs:59:5
    |
 LL |     [1u8, 2].as_mut_ptr() as *mut u8;
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `[1u8, 2].as_mut_ptr()`
 
 error: casting raw pointers to the same type and constness is unnecessary (`*const u32` -> `*const u32`)
-  --> $DIR/unnecessary_cast.rs:51:5
+  --> $DIR/unnecessary_cast.rs:70:5
    |
 LL |     owo::<u32>([1u32].as_ptr()) as *const u32;
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `owo::<u32>([1u32].as_ptr())`
 
 error: casting raw pointers to the same type and constness is unnecessary (`*const u8` -> `*const u8`)
-  --> $DIR/unnecessary_cast.rs:52:5
+  --> $DIR/unnecessary_cast.rs:71:5
    |
 LL |     uwu::<u32, u8>([1u32].as_ptr()) as *const u8;
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `uwu::<u32, u8>([1u32].as_ptr())`
 
 error: casting raw pointers to the same type and constness is unnecessary (`*const u32` -> `*const u32`)
-  --> $DIR/unnecessary_cast.rs:54:5
+  --> $DIR/unnecessary_cast.rs:73:5
    |
 LL |     uwu::<u32, u32>([1u32].as_ptr()) as *const u32;
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `uwu::<u32, u32>([1u32].as_ptr())`
 
 error: casting integer literal to `f32` is unnecessary
-  --> $DIR/unnecessary_cast.rs:116:9
+  --> $DIR/unnecessary_cast.rs:139:9
    |
 LL |         100 as f32;
    |         ^^^^^^^^^^ help: try: `100_f32`
 
 error: casting integer literal to `f64` is unnecessary
-  --> $DIR/unnecessary_cast.rs:117:9
+  --> $DIR/unnecessary_cast.rs:140:9
    |
 LL |         100 as f64;
    |         ^^^^^^^^^^ help: try: `100_f64`
 
 error: casting integer literal to `f64` is unnecessary
-  --> $DIR/unnecessary_cast.rs:118:9
+  --> $DIR/unnecessary_cast.rs:141:9
    |
 LL |         100_i32 as f64;
    |         ^^^^^^^^^^^^^^ help: try: `100_f64`
 
 error: casting integer literal to `f32` is unnecessary
-  --> $DIR/unnecessary_cast.rs:119:17
+  --> $DIR/unnecessary_cast.rs:142:17
    |
 LL |         let _ = -100 as f32;
    |                 ^^^^^^^^^^^ help: try: `-100_f32`
 
 error: casting integer literal to `f64` is unnecessary
-  --> $DIR/unnecessary_cast.rs:120:17
+  --> $DIR/unnecessary_cast.rs:143:17
    |
 LL |         let _ = -100 as f64;
    |                 ^^^^^^^^^^^ help: try: `-100_f64`
 
 error: casting integer literal to `f64` is unnecessary
-  --> $DIR/unnecessary_cast.rs:121:17
+  --> $DIR/unnecessary_cast.rs:144:17
    |
 LL |         let _ = -100_i32 as f64;
    |                 ^^^^^^^^^^^^^^^ help: try: `-100_f64`
 
 error: casting float literal to `f32` is unnecessary
-  --> $DIR/unnecessary_cast.rs:122:9
+  --> $DIR/unnecessary_cast.rs:145:9
    |
 LL |         100. as f32;
    |         ^^^^^^^^^^^ help: try: `100_f32`
 
 error: casting float literal to `f64` is unnecessary
-  --> $DIR/unnecessary_cast.rs:123:9
+  --> $DIR/unnecessary_cast.rs:146:9
    |
 LL |         100. as f64;
    |         ^^^^^^^^^^^ help: try: `100_f64`
 
 error: casting integer literal to `u32` is unnecessary
-  --> $DIR/unnecessary_cast.rs:135:9
+  --> $DIR/unnecessary_cast.rs:158:9
    |
 LL |         1 as u32;
    |         ^^^^^^^^ help: try: `1_u32`
 
 error: casting integer literal to `i32` is unnecessary
-  --> $DIR/unnecessary_cast.rs:136:9
+  --> $DIR/unnecessary_cast.rs:159:9
    |
 LL |         0x10 as i32;
    |         ^^^^^^^^^^^ help: try: `0x10_i32`
 
 error: casting integer literal to `usize` is unnecessary
-  --> $DIR/unnecessary_cast.rs:137:9
+  --> $DIR/unnecessary_cast.rs:160:9
    |
 LL |         0b10 as usize;
    |         ^^^^^^^^^^^^^ help: try: `0b10_usize`
 
 error: casting integer literal to `u16` is unnecessary
-  --> $DIR/unnecessary_cast.rs:138:9
+  --> $DIR/unnecessary_cast.rs:161:9
    |
 LL |         0o73 as u16;
    |         ^^^^^^^^^^^ help: try: `0o73_u16`
 
 error: casting integer literal to `u32` is unnecessary
-  --> $DIR/unnecessary_cast.rs:139:9
+  --> $DIR/unnecessary_cast.rs:162:9
    |
 LL |         1_000_000_000 as u32;
    |         ^^^^^^^^^^^^^^^^^^^^ help: try: `1_000_000_000_u32`
 
 error: casting float literal to `f64` is unnecessary
-  --> $DIR/unnecessary_cast.rs:141:9
+  --> $DIR/unnecessary_cast.rs:164:9
    |
 LL |         1.0 as f64;
    |         ^^^^^^^^^^ help: try: `1.0_f64`
 
 error: casting float literal to `f32` is unnecessary
-  --> $DIR/unnecessary_cast.rs:142:9
+  --> $DIR/unnecessary_cast.rs:165:9
    |
 LL |         0.5 as f32;
    |         ^^^^^^^^^^ help: try: `0.5_f32`
 
 error: casting integer literal to `i32` is unnecessary
-  --> $DIR/unnecessary_cast.rs:146:17
+  --> $DIR/unnecessary_cast.rs:169:17
    |
 LL |         let _ = -1 as i32;
    |                 ^^^^^^^^^ help: try: `-1_i32`
 
 error: casting float literal to `f32` is unnecessary
-  --> $DIR/unnecessary_cast.rs:147:17
+  --> $DIR/unnecessary_cast.rs:170:17
    |
 LL |         let _ = -1.0 as f32;
    |                 ^^^^^^^^^^^ help: try: `-1.0_f32`
 
 error: casting to the same type is unnecessary (`i32` -> `i32`)
-  --> $DIR/unnecessary_cast.rs:153:18
+  --> $DIR/unnecessary_cast.rs:176:18
    |
 LL |         let _ = &(x as i32);
    |                  ^^^^^^^^^^ help: try: `{ x }`
 
 error: casting integer literal to `i32` is unnecessary
-  --> $DIR/unnecessary_cast.rs:159:22
+  --> $DIR/unnecessary_cast.rs:182:22
    |
 LL |         let _: i32 = -(1) as i32;
    |                      ^^^^^^^^^^^ help: try: `-1_i32`
 
 error: casting integer literal to `i64` is unnecessary
-  --> $DIR/unnecessary_cast.rs:161:22
+  --> $DIR/unnecessary_cast.rs:184:22
    |
 LL |         let _: i64 = -(1) as i64;
    |                      ^^^^^^^^^^^ help: try: `-1_i64`
 
 error: casting float literal to `f64` is unnecessary
-  --> $DIR/unnecessary_cast.rs:168:22
+  --> $DIR/unnecessary_cast.rs:191:22
    |
 LL |         let _: f64 = (-8.0 as f64).exp();
    |                      ^^^^^^^^^^^^^ help: try: `(-8.0_f64)`
 
 error: casting float literal to `f64` is unnecessary
-  --> $DIR/unnecessary_cast.rs:170:23
+  --> $DIR/unnecessary_cast.rs:193:23
    |
 LL |         let _: f64 = -(8.0 as f64).exp(); // should suggest `-8.0_f64.exp()` here not to change code behavior
    |                       ^^^^^^^^^^^^ help: try: `8.0_f64`
 
 error: casting to the same type is unnecessary (`f32` -> `f32`)
-  --> $DIR/unnecessary_cast.rs:178:20
+  --> $DIR/unnecessary_cast.rs:201:20
    |
 LL |         let _num = foo() as f32;
    |                    ^^^^^^^^^^^^ help: try: `foo()`