Move some cases from redundant_slicing to deref_by_slicing

clippy_lints/src/redundant_slicing.rs

@@ -6,7 +6,7 @@ use if_chain::if_chain;
 use rustc_ast::util::parser::PREC_PREFIX;
 use rustc_errors::Applicability;
 use rustc_hir::{BorrowKind, Expr, ExprKind, LangItem, Mutability};
-use rustc_lint::{LateContext, LateLintPass};
+use rustc_lint::{LateContext, LateLintPass, Lint};
 use rustc_middle::ty::adjustment::{Adjust, AutoBorrow, AutoBorrowMutability};
 use rustc_middle::ty::subst::GenericArg;
 use rustc_session::{declare_lint_pass, declare_tool_lint};
@@ -44,7 +44,7 @@ declare_clippy_lint! {
 
 declare_clippy_lint! {
     /// ### What it does
-    /// Checks for slicing expression which are equivalent to dereferencing the
+    /// Checks for slicing expressions which are equivalent to dereferencing the
     /// value.
     ///
     /// ### Why is this bad?
@@ -68,6 +68,9 @@ declare_clippy_lint! {
 
 declare_lint_pass!(RedundantSlicing => [REDUNDANT_SLICING, DEREF_BY_SLICING]);
 
+static REDUNDANT_SLICING_LINT: (&Lint, &str) = (REDUNDANT_SLICING, "redundant slicing of the whole range");
+static DEREF_BY_SLICING_LINT: (&Lint, &str) = (DEREF_BY_SLICING, "slicing when dereferencing would work");
+
 impl<'tcx> LateLintPass<'tcx> for RedundantSlicing {
     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
         if expr.span.from_expansion() {
@@ -89,7 +92,7 @@ impl<'tcx> LateLintPass<'tcx> for RedundantSlicing {
                 });
                 let mut app = Applicability::MachineApplicable;
 
-                let (lint, msg, help, sugg) = if expr_ty == indexed_ty {
+                let ((lint, msg), help, sugg) = if expr_ty == indexed_ty {
                     if expr_ref_count > indexed_ref_count {
                         // Indexing takes self by reference and can't return a reference to that
                         // reference as it's a local variable. The only way this could happen is if
@@ -100,9 +103,9 @@ impl<'tcx> LateLintPass<'tcx> for RedundantSlicing {
                     }
                     let deref_count = indexed_ref_count - expr_ref_count;
 
-                    let (reborrow_str, help_str) = if mutability == Mutability::Mut {
+                    let (lint, reborrow_str, help_str) = if mutability == Mutability::Mut {
                         // The slice was used to reborrow the mutable reference.
-                        ("&mut *", "reborrow the original value instead")
+                        (DEREF_BY_SLICING_LINT, "&mut *", "reborrow the original value instead")
                     } else if matches!(
                         parent_expr,
                         Some(Expr {
@@ -113,11 +116,11 @@ impl<'tcx> LateLintPass<'tcx> for RedundantSlicing {
                         matches!(a.kind, Adjust::Borrow(AutoBorrow::Ref(_, AutoBorrowMutability::Mut { .. })))
                     }) {
                         // The slice was used to make a temporary reference.
-                        ("&*", "reborrow the original value instead")
+                        (DEREF_BY_SLICING_LINT, "&*", "reborrow the original value instead")
                     } else if deref_count != 0 {
-                        ("", "dereference the original value instead")
+                        (DEREF_BY_SLICING_LINT, "", "dereference the original value instead")
                     } else {
-                        ("", "use the original value instead")
+                        (REDUNDANT_SLICING_LINT, "", "use the original value instead")
                     };
 
                     let snip = snippet_with_context(cx, indexed.span, ctxt, "..", &mut app).0;
@@ -127,7 +130,7 @@ impl<'tcx> LateLintPass<'tcx> for RedundantSlicing {
                         format!("{}{}{}", reborrow_str, "*".repeat(deref_count), snip)
                     };
 
-                    (REDUNDANT_SLICING, "redundant slicing of the whole range", help_str, sugg)
+                    (lint, help_str, sugg)
                 } else if let Some(target_id) = cx.tcx.lang_items().deref_target() {
                     if let Ok(deref_ty) = cx.tcx.try_normalize_erasing_regions(
                         cx.param_env,
@@ -140,7 +143,7 @@ impl<'tcx> LateLintPass<'tcx> for RedundantSlicing {
                             } else {
                                 format!("&{}{}*{}", mutability.prefix_str(), "*".repeat(indexed_ref_count), snip)
                             };
-                            (DEREF_BY_SLICING, "slicing when dereferencing would work", "dereference the original value instead", sugg)
+                            (DEREF_BY_SLICING_LINT, "dereference the original value instead", sugg)
                         } else {
                             return;
                         }

tests/ui/deref_by_slicing.fixed

@@ -2,6 +2,8 @@
 
 #![warn(clippy::deref_by_slicing)]
 
+use std::io::Read;
+
 fn main() {
     let mut vec = vec![0];
     let _ = &*vec;
@@ -9,8 +11,19 @@ fn main() {
 
     let ref_vec = &mut vec;
     let _ = &**ref_vec;
-    let _ = &mut **ref_vec;
+    let mut_slice = &mut **ref_vec;
+    let _ = &mut *mut_slice; // Err, re-borrows slice
 
     let s = String::new();
     let _ = &*s;
+
+    static S: &[u8] = &[0, 1, 2];
+    let _ = &mut &*S; // Err, re-borrows slice
+
+    let slice: &[u32] = &[0u32, 1u32];
+    let slice_ref = &slice;
+    let _ = *slice_ref; // Err, derefs slice
+
+    let bytes: &[u8] = &[];
+    let _ = (&*bytes).read_to_end(&mut vec![]).unwrap(); // Err, re-borrows slice
 }

tests/ui/deref_by_slicing.rs

@@ -2,6 +2,8 @@
 
 #![warn(clippy::deref_by_slicing)]
 
+use std::io::Read;
+
 fn main() {
     let mut vec = vec![0];
     let _ = &vec[..];
@@ -9,8 +11,19 @@ fn main() {
 
     let ref_vec = &mut vec;
     let _ = &ref_vec[..];
-    let _ = &mut ref_vec[..];
+    let mut_slice = &mut ref_vec[..];
+    let _ = &mut mut_slice[..]; // Err, re-borrows slice
 
     let s = String::new();
     let _ = &s[..];
+
+    static S: &[u8] = &[0, 1, 2];
+    let _ = &mut &S[..]; // Err, re-borrows slice
+
+    let slice: &[u32] = &[0u32, 1u32];
+    let slice_ref = &slice;
+    let _ = &slice_ref[..]; // Err, derefs slice
+
+    let bytes: &[u8] = &[];
+    let _ = (&bytes[..]).read_to_end(&mut vec![]).unwrap(); // Err, re-borrows slice
 }

tests/ui/deref_by_slicing.stderr

@@ -1,5 +1,5 @@
 error: slicing when dereferencing would work
-  --> $DIR/deref_by_slicing.rs:7:13
+  --> $DIR/deref_by_slicing.rs:9:13
    |
 LL |     let _ = &vec[..];
    |             ^^^^^^^^ help: dereference the original value instead: `&*vec`
@@ -7,28 +7,52 @@ LL |     let _ = &vec[..];
    = note: `-D clippy::deref-by-slicing` implied by `-D warnings`
 
 error: slicing when dereferencing would work
-  --> $DIR/deref_by_slicing.rs:8:13
+  --> $DIR/deref_by_slicing.rs:10:13
    |
 LL |     let _ = &mut vec[..];
    |             ^^^^^^^^^^^^ help: dereference the original value instead: `&mut *vec`
 
 error: slicing when dereferencing would work
-  --> $DIR/deref_by_slicing.rs:11:13
+  --> $DIR/deref_by_slicing.rs:13:13
    |
 LL |     let _ = &ref_vec[..];
    |             ^^^^^^^^^^^^ help: dereference the original value instead: `&**ref_vec`
 
 error: slicing when dereferencing would work
-  --> $DIR/deref_by_slicing.rs:12:13
+  --> $DIR/deref_by_slicing.rs:14:21
    |
-LL |     let _ = &mut ref_vec[..];
+LL |     let mut_slice = &mut ref_vec[..];
-   |             ^^^^^^^^^^^^^^^^ help: dereference the original value instead: `&mut **ref_vec`
+   |                     ^^^^^^^^^^^^^^^^ help: dereference the original value instead: `&mut **ref_vec`
 
 error: slicing when dereferencing would work
   --> $DIR/deref_by_slicing.rs:15:13
    |
+LL |     let _ = &mut mut_slice[..]; // Err, re-borrows slice
+   |             ^^^^^^^^^^^^^^^^^^ help: reborrow the original value instead: `&mut *mut_slice`
+
+error: slicing when dereferencing would work
+  --> $DIR/deref_by_slicing.rs:18:13
+   |
 LL |     let _ = &s[..];
    |             ^^^^^^ help: dereference the original value instead: `&*s`
 
-error: aborting due to 5 previous errors
+error: slicing when dereferencing would work
+  --> $DIR/deref_by_slicing.rs:21:18
+   |
+LL |     let _ = &mut &S[..]; // Err, re-borrows slice
+   |                  ^^^^^^ help: reborrow the original value instead: `&*S`
+
+error: slicing when dereferencing would work
+  --> $DIR/deref_by_slicing.rs:25:13
+   |
+LL |     let _ = &slice_ref[..]; // Err, derefs slice
+   |             ^^^^^^^^^^^^^^ help: dereference the original value instead: `*slice_ref`
+
+error: slicing when dereferencing would work
+  --> $DIR/deref_by_slicing.rs:28:13
+   |
+LL |     let _ = (&bytes[..]).read_to_end(&mut vec![]).unwrap(); // Err, re-borrows slice
+   |             ^^^^^^^^^^^^ help: reborrow the original value instead: `(&*bytes)`
+
+error: aborting due to 9 previous errors
 

tests/ui/redundant_slicing.fixed

@@ -14,11 +14,11 @@ fn main() {
     let _ = (&*v); // Outer borrow is redundant
 
     static S: &[u8] = &[0, 1, 2];
-    let err = &mut &*S; // Should reborrow instead of slice
+    let _ = &mut &S[..]; // Ok, re-borrows slice
 
     let mut vec = vec![0];
     let mut_slice = &mut vec[..]; // Ok, results in `&mut [_]`
-    let _ = &mut *mut_slice; // Should reborrow instead of slice
+    let _ = &mut mut_slice[..]; // Ok, re-borrows slice
 
     let ref_vec = &vec;
     let _ = &ref_vec[..]; // Ok, results in `&[_]`
@@ -38,9 +38,9 @@ fn main() {
     let _ = m2!(slice); // Don't lint in a macro
 
     let slice_ref = &slice;
-    let _ = *slice_ref; // Deref instead of slice
+    let _ = &slice_ref[..]; // Ok, derefs slice
 
     // Issue #7972
     let bytes: &[u8] = &[];
-    let _ = (&*bytes).read_to_end(&mut vec![]).unwrap();
+    let _ = (&bytes[..]).read_to_end(&mut vec![]).unwrap(); // Ok, re-borrows slice
 }

tests/ui/redundant_slicing.rs

@@ -14,11 +14,11 @@ fn main() {
     let _ = &(&*v)[..]; // Outer borrow is redundant
 
     static S: &[u8] = &[0, 1, 2];
-    let err = &mut &S[..]; // Should reborrow instead of slice
+    let _ = &mut &S[..]; // Ok, re-borrows slice
 
     let mut vec = vec![0];
     let mut_slice = &mut vec[..]; // Ok, results in `&mut [_]`
-    let _ = &mut mut_slice[..]; // Should reborrow instead of slice
+    let _ = &mut mut_slice[..]; // Ok, re-borrows slice
 
     let ref_vec = &vec;
     let _ = &ref_vec[..]; // Ok, results in `&[_]`
@@ -38,9 +38,9 @@ fn main() {
     let _ = m2!(slice); // Don't lint in a macro
 
     let slice_ref = &slice;
-    let _ = &slice_ref[..]; // Deref instead of slice
+    let _ = &slice_ref[..]; // Ok, derefs slice
 
     // Issue #7972
     let bytes: &[u8] = &[];
-    let _ = (&bytes[..]).read_to_end(&mut vec![]).unwrap();
+    let _ = (&bytes[..]).read_to_end(&mut vec![]).unwrap(); // Ok, re-borrows slice
 }

tests/ui/redundant_slicing.stderr

@@ -12,35 +12,11 @@ error: redundant slicing of the whole range
 LL |     let _ = &(&*v)[..]; // Outer borrow is redundant
    |             ^^^^^^^^^^ help: use the original value instead: `(&*v)`
 
-error: redundant slicing of the whole range
-  --> $DIR/redundant_slicing.rs:17:20
-   |
-LL |     let err = &mut &S[..]; // Should reborrow instead of slice
-   |                    ^^^^^^ help: reborrow the original value instead: `&*S`
-
-error: redundant slicing of the whole range
-  --> $DIR/redundant_slicing.rs:21:13
-   |
-LL |     let _ = &mut mut_slice[..]; // Should reborrow instead of slice
-   |             ^^^^^^^^^^^^^^^^^^ help: reborrow the original value instead: `&mut *mut_slice`
-
 error: redundant slicing of the whole range
   --> $DIR/redundant_slicing.rs:31:13
    |
 LL |     let _ = &m!(slice)[..];
    |             ^^^^^^^^^^^^^^ help: use the original value instead: `slice`
 
-error: redundant slicing of the whole range
+error: aborting due to 3 previous errors
-  --> $DIR/redundant_slicing.rs:41:13
-   |
-LL |     let _ = &slice_ref[..]; // Deref instead of slice
-   |             ^^^^^^^^^^^^^^ help: dereference the original value instead: `*slice_ref`
-
-error: redundant slicing of the whole range
-  --> $DIR/redundant_slicing.rs:45:13
-   |
-LL |     let _ = (&bytes[..]).read_to_end(&mut vec![]).unwrap();
-   |             ^^^^^^^^^^^^ help: reborrow the original value instead: `(&*bytes)`
-
-error: aborting due to 7 previous errors