Rollup merge of rust-lang#126604 - kadiwa4:uplift_double_negation, r=nnethercote

Uplift `clippy::double_neg` lint as `double_negations`

Warns about cases like this:
```rust
fn main() {
    let x = 1;
    let _b = --x; //~ WARN use of a double negation
}
```

The intent is to keep people from thinking that `--x` is a prefix decrement operator. `++x`, `x++` and `x--` are invalid expressions and already have a helpful diagnostic.

I didn't add a machine-applicable suggestion to the lint because it's not entirely clear what the programmer was trying to achieve with the `--x` operation. The code that triggers the lint should always be reviewed manually.

Closes rust-lang#82987

Author: fmease

.github/driver.sh

@@ -47,9 +47,9 @@ unset CARGO_MANIFEST_DIR
 
 # Run a lint and make sure it produces the expected output. It's also expected to exit with code 1
 # FIXME: How to match the clippy invocation in compile-test.rs?
-./target/debug/clippy-driver -Dwarnings -Aunused -Zui-testing --emit metadata --crate-type bin tests/ui/double_neg.rs 2>double_neg.stderr && exit 1
-sed -e "/= help: for/d" double_neg.stderr > normalized.stderr
-diff -u normalized.stderr tests/ui/double_neg.stderr
+./target/debug/clippy-driver -Dwarnings -Aunused -Zui-testing --emit metadata --crate-type bin tests/ui/box_default.rs 2>box_default.stderr && exit 1
+sed -e "/= help: for/d" box_default.stderr > normalized.stderr
+diff -u normalized.stderr tests/ui/box_default.stderr
 
 # make sure "clippy-driver --rustc --arg" and "rustc --arg" behave the same
 SYSROOT=$(rustc --print sysroot)

book/src/usage.md

@@ -33,7 +33,7 @@ You can configure lint levels on the command line by adding
 `-A/W/D clippy::lint_name` like this:
 
 ```bash
-cargo clippy -- -Aclippy::style -Wclippy::double_neg -Dclippy::perf
+cargo clippy -- -Aclippy::style -Wclippy::box_default -Dclippy::perf
 ```
 
 For [CI] all warnings can be elevated to errors which will in turn fail
@@ -101,11 +101,10 @@ You can configure lint levels in source code the same way you can configure
 ```rust,ignore
 #![allow(clippy::style)]
 
-#[warn(clippy::double_neg)]
+#[warn(clippy::box_default)]
 fn main() {
-    let x = 1;
-    let y = --x;
-    //      ^^ warning: double negation
+    let _ = Box::<String>::new(Default::default());
+    // ^ warning: `Box::new(_)` of default value
 }
 ```
 

clippy_dev/src/new_lint.rs

@@ -455,7 +455,7 @@ fn setup_mod_file(path: &Path, lint: &LintData<'_>) -> io::Result<&'static str>
     });
 
     // Find both the last lint declaration (declare_clippy_lint!) and the lint pass impl
-    while let Some(LintDeclSearchResult { content, .. }) = iter.find(|result| result.token == TokenKind::Ident) {
+    while let Some(LintDeclSearchResult { content, .. }) = iter.find(|result| result.token_kind == TokenKind::Ident) {
         let mut iter = iter
             .by_ref()
             .filter(|t| !matches!(t.token_kind, TokenKind::Whitespace | TokenKind::LineComment { .. }));
@@ -465,7 +465,7 @@ fn setup_mod_file(path: &Path, lint: &LintData<'_>) -> io::Result<&'static str>
                 // matches `!{`
                 match_tokens!(iter, Bang OpenBrace);
                 if let Some(LintDeclSearchResult { range, .. }) =
-                    iter.find(|result| result.token == TokenKind::CloseBrace)
+                    iter.find(|result| result.token_kind == TokenKind::CloseBrace)
                 {
                     last_decl_curly_offset = Some(range.end);
                 }

clippy_lints/src/declared_lints.rs

@@ -507,7 +507,6 @@ pub static LINTS: &[&crate::LintInfo] = &[
     crate::misc::USED_UNDERSCORE_BINDING_INFO,
     crate::misc::USED_UNDERSCORE_ITEMS_INFO,
     crate::misc_early::BUILTIN_TYPE_SHADOW_INFO,
-    crate::misc_early::DOUBLE_NEG_INFO,
     crate::misc_early::DUPLICATE_UNDERSCORE_ARGUMENT_INFO,
     crate::misc_early::MIXED_CASE_HEX_LITERALS_INFO,
     crate::misc_early::REDUNDANT_AT_REST_PATTERN_INFO,

clippy_lints/src/deprecated_lints.rs

@@ -129,6 +129,8 @@ declare_with_version! { RENAMED(RENAMED_VERSION): &[(&str, &str)] = &[
     ("clippy::clone_double_ref", "suspicious_double_ref_op"),
     #[clippy::version = ""]
     ("clippy::cmp_nan", "invalid_nan_comparisons"),
+    #[clippy::version = "1.86.0"]
+    ("clippy::double_neg", "double_negations"),
     #[clippy::version = ""]
     ("clippy::drop_bounds", "drop_bounds"),
     #[clippy::version = ""]

clippy_lints/src/misc_early/double_neg.rs

@@ -1,5 +1,4 @@
 mod builtin_type_shadow;
-mod double_neg;
 mod literal_suffix;
 mod mixed_case_hex_literals;
 mod redundant_at_rest_pattern;
@@ -85,25 +84,6 @@ declare_clippy_lint! {
     "function arguments having names which only differ by an underscore"
 }
 
-declare_clippy_lint! {
-    /// ### What it does
-    /// Detects expressions of the form `--x`.
-    ///
-    /// ### Why is this bad?
-    /// It can mislead C/C++ programmers to think `x` was
-    /// decremented.
-    ///
-    /// ### Example
-    /// ```no_run
-    /// let mut x = 3;
-    /// --x;
-    /// ```
-    #[clippy::version = "pre 1.29.0"]
-    pub DOUBLE_NEG,
-    style,
-    "`--x`, which is a double negation of `x` and not a pre-decrement as in C/C++"
-}
-
 declare_clippy_lint! {
     /// ### What it does
     /// Warns on hexadecimal literals with mixed-case letter
@@ -352,7 +332,6 @@ declare_clippy_lint! {
 declare_lint_pass!(MiscEarlyLints => [
     UNNEEDED_FIELD_PATTERN,
     DUPLICATE_UNDERSCORE_ARGUMENT,
-    DOUBLE_NEG,
     MIXED_CASE_HEX_LITERALS,
     UNSEPARATED_LITERAL_SUFFIX,
     SEPARATED_LITERAL_SUFFIX,
@@ -415,7 +394,6 @@ impl EarlyLintPass for MiscEarlyLints {
         if let ExprKind::Lit(lit) = expr.kind {
             MiscEarlyLints::check_lit(cx, lit, expr.span);
         }
-        double_neg::check(cx, expr);
     }
 }
 

clippy_lints/src/misc_early/mod.rs

@@ -13,9 +13,8 @@
 #![allow(clippy::disallowed_methods)]
 #![allow(clippy::disallowed_types)]
 #![allow(clippy::mixed_read_write_in_expression)]
-#![allow(clippy::manual_find_map)]
 #![allow(clippy::manual_filter_map)]
-#![allow(unpredictable_function_pointer_comparisons)]
+#![allow(clippy::manual_find_map)]
 #![allow(clippy::useless_conversion)]
 #![allow(clippy::redundant_pattern_matching)]
 #![allow(clippy::match_result_ok)]
@@ -30,6 +29,7 @@
 #![allow(clippy::unwrap_used)]
 #![allow(clippy::panicking_overflow_checks)]
 #![allow(clippy::needless_borrow)]
+#![allow(clippy::reversed_empty_ranges)]
 #![allow(clippy::single_char_add_str)]
 #![allow(clippy::module_name_repetitions)]
 #![allow(clippy::missing_const_for_thread_local)]
@@ -39,9 +39,11 @@
 #![allow(invalid_reference_casting)]
 #![allow(suspicious_double_ref_op)]
 #![allow(invalid_nan_comparisons)]
+#![allow(double_negations)]
 #![allow(drop_bounds)]
 #![allow(dropping_copy_types)]
 #![allow(dropping_references)]
+#![allow(unpredictable_function_pointer_comparisons)]
 #![allow(useless_ptr_null_checks)]
 #![allow(for_loops_over_fallibles)]
 #![allow(forgetting_copy_types)]
@@ -60,8 +62,6 @@
 #![allow(unknown_lints)]
 #![allow(unused_labels)]
 #![allow(ambiguous_wide_pointer_comparisons)]
-#![allow(unpredictable_function_pointer_comparisons)]
-#![allow(clippy::reversed_empty_ranges)]
 #![warn(clippy::almost_complete_range)] //~ ERROR: lint `clippy::almost_complete_letter_range`
 #![warn(clippy::disallowed_names)] //~ ERROR: lint `clippy::blacklisted_name`
 #![warn(clippy::blocks_in_conditions)] //~ ERROR: lint `clippy::block_in_if_condition_expr`
@@ -74,9 +74,8 @@
 #![warn(clippy::disallowed_methods)] //~ ERROR: lint `clippy::disallowed_method`
 #![warn(clippy::disallowed_types)] //~ ERROR: lint `clippy::disallowed_type`
 #![warn(clippy::mixed_read_write_in_expression)] //~ ERROR: lint `clippy::eval_order_dependence`
-#![warn(clippy::manual_find_map)] //~ ERROR: lint `clippy::find_map`
 #![warn(clippy::manual_filter_map)] //~ ERROR: lint `clippy::filter_map`
-#![warn(unpredictable_function_pointer_comparisons)] //~ ERROR: lint `clippy::fn_address_comparisons`
+#![warn(clippy::manual_find_map)] //~ ERROR: lint `clippy::find_map`
 #![warn(clippy::useless_conversion)] //~ ERROR: lint `clippy::identity_conversion`
 #![warn(clippy::redundant_pattern_matching)] //~ ERROR: lint `clippy::if_let_redundant_pattern_matching`
 #![warn(clippy::match_result_ok)] //~ ERROR: lint `clippy::if_let_some_result`
@@ -95,6 +94,7 @@
 #![warn(clippy::expect_used)] //~ ERROR: lint `clippy::result_expect_used`
 #![warn(clippy::map_unwrap_or)] //~ ERROR: lint `clippy::result_map_unwrap_or_else`
 #![warn(clippy::unwrap_used)] //~ ERROR: lint `clippy::result_unwrap_used`
+#![warn(clippy::reversed_empty_ranges)] //~ ERROR: lint `clippy::reverse_range_loop`
 #![warn(clippy::single_char_add_str)] //~ ERROR: lint `clippy::single_char_push_str`
 #![warn(clippy::module_name_repetitions)] //~ ERROR: lint `clippy::stutter`
 #![warn(clippy::missing_const_for_thread_local)] //~ ERROR: lint `clippy::thread_local_initializer_can_be_made_const`
@@ -104,9 +104,11 @@
 #![warn(invalid_reference_casting)] //~ ERROR: lint `clippy::cast_ref_to_mut`
 #![warn(suspicious_double_ref_op)] //~ ERROR: lint `clippy::clone_double_ref`
 #![warn(invalid_nan_comparisons)] //~ ERROR: lint `clippy::cmp_nan`
+#![warn(double_negations)] //~ ERROR: lint `clippy::double_neg`
 #![warn(drop_bounds)] //~ ERROR: lint `clippy::drop_bounds`
 #![warn(dropping_copy_types)] //~ ERROR: lint `clippy::drop_copy`
 #![warn(dropping_references)] //~ ERROR: lint `clippy::drop_ref`
+#![warn(unpredictable_function_pointer_comparisons)] //~ ERROR: lint `clippy::fn_address_comparisons`
 #![warn(useless_ptr_null_checks)] //~ ERROR: lint `clippy::fn_null_check`
 #![warn(for_loops_over_fallibles)] //~ ERROR: lint `clippy::for_loop_over_option`
 #![warn(for_loops_over_fallibles)] //~ ERROR: lint `clippy::for_loop_over_result`
@@ -128,6 +130,5 @@
 #![warn(unknown_lints)] //~ ERROR: lint `clippy::unknown_clippy_lints`
 #![warn(unused_labels)] //~ ERROR: lint `clippy::unused_label`
 #![warn(ambiguous_wide_pointer_comparisons)] //~ ERROR: lint `clippy::vtable_address_comparisons`
-#![warn(clippy::reversed_empty_ranges)] //~ ERROR: lint `clippy::reverse_range_loop`
 
 fn main() {}