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Auto merge of rust-lang#10810 - samueltardieu:needless-else, r=llogiq
needless_else: new lint to check for empty `else` clauses Empty `else` clauses are useless. They happen in the wild and are not linted yet: https://github.com/uutils/coreutils/pull/4880/files `else` clauses containing or preceded by comments are not linted as the comments might be important. changelog: [`needless_else`]: new lint
2 parents fe792d9 + e6646eb commit 97598e9

18 files changed

+231
-70
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‎CHANGELOG.md‎

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@@ -4874,6 +4874,7 @@ Released 2018-09-13
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[`needless_collect`]: https://rust-lang.github.io/rust-clippy/master/index.html#needless_collect
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[`needless_continue`]: https://rust-lang.github.io/rust-clippy/master/index.html#needless_continue
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[`needless_doctest_main`]: https://rust-lang.github.io/rust-clippy/master/index.html#needless_doctest_main
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[`needless_else`]: https://rust-lang.github.io/rust-clippy/master/index.html#needless_else
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[`needless_for_each`]: https://rust-lang.github.io/rust-clippy/master/index.html#needless_for_each
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[`needless_late_init`]: https://rust-lang.github.io/rust-clippy/master/index.html#needless_late_init
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[`needless_lifetimes`]: https://rust-lang.github.io/rust-clippy/master/index.html#needless_lifetimes

‎clippy_lints/src/declared_lints.rs‎

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@@ -449,6 +449,7 @@ pub(crate) static LINTS: &[&crate::LintInfo] = &[
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crate::needless_bool::NEEDLESS_BOOL_ASSIGN_INFO,
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crate::needless_borrowed_ref::NEEDLESS_BORROWED_REFERENCE_INFO,
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crate::needless_continue::NEEDLESS_CONTINUE_INFO,
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crate::needless_else::NEEDLESS_ELSE_INFO,
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crate::needless_for_each::NEEDLESS_FOR_EACH_INFO,
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crate::needless_late_init::NEEDLESS_LATE_INIT_INFO,
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crate::needless_parens_on_range_literals::NEEDLESS_PARENS_ON_RANGE_LITERALS_INFO,

‎clippy_lints/src/lib.rs‎

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@@ -218,6 +218,7 @@ mod needless_arbitrary_self_type;
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mod needless_bool;
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mod needless_borrowed_ref;
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mod needless_continue;
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mod needless_else;
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mod needless_for_each;
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mod needless_late_init;
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mod needless_parens_on_range_literals;
@@ -992,6 +993,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
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store.register_late_pass(|_| Box::new(items_after_test_module::ItemsAfterTestModule));
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store.register_early_pass(|| Box::new(ref_patterns::RefPatterns));
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store.register_late_pass(|_| Box::new(default_constructed_unit_structs::DefaultConstructedUnitStructs));
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store.register_early_pass(|| Box::new(needless_else::NeedlessElse));
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// add lints here, do not remove this comment, it's used in `new_lint`
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}
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‎clippy_lints/src/needless_else.rs‎

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@@ -0,0 +1,57 @@
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use clippy_utils::{diagnostics::span_lint_and_sugg, source::trim_span, span_extract_comment};
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use rustc_ast::ast::{Expr, ExprKind};
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use rustc_errors::Applicability;
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use rustc_lint::{EarlyContext, EarlyLintPass, LintContext};
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use rustc_session::{declare_lint_pass, declare_tool_lint};
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declare_clippy_lint! {
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/// ### What it does
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/// Checks for empty `else` branches.
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///
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/// ### Why is this bad?
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/// An empty else branch does nothing and can be removed.
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///
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/// ### Example
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/// ```rust
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///# fn check() -> bool { true }
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/// if check() {
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/// println!("Check successful!");
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/// } else {
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/// }
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/// ```
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/// Use instead:
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/// ```rust
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///# fn check() -> bool { true }
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/// if check() {
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/// println!("Check successful!");
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/// }
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/// ```
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#[clippy::version = "1.71.0"]
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pub NEEDLESS_ELSE,
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style,
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"empty else branch"
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}
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declare_lint_pass!(NeedlessElse => [NEEDLESS_ELSE]);
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impl EarlyLintPass for NeedlessElse {
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fn check_expr(&mut self, cx: &EarlyContext<'_>, expr: &Expr) {
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if let ExprKind::If(_, then_block, Some(else_clause)) = &expr.kind &&
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let ExprKind::Block(block, _) = &else_clause.kind &&
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!expr.span.from_expansion() &&
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!else_clause.span.from_expansion() &&
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block.stmts.is_empty() {
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let span = trim_span(cx.sess().source_map(), expr.span.trim_start(then_block.span).unwrap());
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if span_extract_comment(cx.sess().source_map(), span).is_empty() {
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span_lint_and_sugg(
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cx,
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NEEDLESS_ELSE,
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span,
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"this else branch is empty",
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"you can remove it",
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String::new(),
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Applicability::MachineApplicable,
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);
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}
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}
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}
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}

‎tests/ui-toml/ifs_same_cond/ifs_same_cond.rs‎

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@@ -1,5 +1,5 @@
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#![warn(clippy::ifs_same_cond)]
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#![allow(clippy::if_same_then_else, clippy::comparison_chain)]
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#![allow(clippy::if_same_then_else, clippy::comparison_chain, clippy::needless_else)]
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fn main() {}
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‎tests/ui/branches_sharing_code/valid_if_blocks.rs‎

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@@ -1,6 +1,10 @@
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#![deny(clippy::branches_sharing_code, clippy::if_same_then_else)]
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#![allow(dead_code)]
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#![allow(clippy::mixed_read_write_in_expression, clippy::uninlined_format_args)]
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#![allow(
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clippy::mixed_read_write_in_expression,
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clippy::uninlined_format_args,
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clippy::needless_else
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)]
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// This tests valid if blocks that shouldn't trigger the lint
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‎tests/ui/branches_sharing_code/valid_if_blocks.stderr‎

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@@ -1,13 +1,13 @@
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error: this `if` has identical blocks
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--> $DIR/valid_if_blocks.rs:105:14
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--> $DIR/valid_if_blocks.rs:109:14
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|
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LL | if false {
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| ______________^
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LL | | } else {
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| |_____^
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|
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note: same as this
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--> $DIR/valid_if_blocks.rs:106:12
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--> $DIR/valid_if_blocks.rs:110:12
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|
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LL | } else {
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| ____________^
@@ -20,7 +20,7 @@ LL | #![deny(clippy::branches_sharing_code, clippy::if_same_then_else)]
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| ^^^^^^^^^^^^^^^^^^^^^^^^^
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error: this `if` has identical blocks
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--> $DIR/valid_if_blocks.rs:116:15
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--> $DIR/valid_if_blocks.rs:120:15
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|
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LL | if x == 0 {
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| _______________^
@@ -31,7 +31,7 @@ LL | | } else {
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| |_____^
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|
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note: same as this
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--> $DIR/valid_if_blocks.rs:120:12
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--> $DIR/valid_if_blocks.rs:124:12
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|
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LL | } else {
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| ____________^
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| |_____^
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error: this `if` has identical blocks
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--> $DIR/valid_if_blocks.rs:127:23
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--> $DIR/valid_if_blocks.rs:131:23
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|
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LL | let _ = if x == 6 { 7 } else { 7 };
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| ^^^^^
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|
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note: same as this
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--> $DIR/valid_if_blocks.rs:127:34
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--> $DIR/valid_if_blocks.rs:131:34
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|
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LL | let _ = if x == 6 { 7 } else { 7 };
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| ^^^^^
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error: this `if` has identical blocks
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--> $DIR/valid_if_blocks.rs:133:23
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--> $DIR/valid_if_blocks.rs:137:23
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|
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LL | } else if x == 68 {
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| _______________________^
@@ -66,7 +66,7 @@ LL | | } else {
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| |_____^
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|
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note: same as this
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--> $DIR/valid_if_blocks.rs:138:12
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--> $DIR/valid_if_blocks.rs:142:12
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|
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LL | } else {
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| ____________^
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| |_____^
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error: this `if` has identical blocks
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--> $DIR/valid_if_blocks.rs:147:23
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--> $DIR/valid_if_blocks.rs:151:23
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|
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LL | } else if x == 68 {
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| _______________________^
@@ -88,7 +88,7 @@ LL | | } else {
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| |_____^
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|
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note: same as this
91-
--> $DIR/valid_if_blocks.rs:150:12
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--> $DIR/valid_if_blocks.rs:154:12
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|
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LL | } else {
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| ____________^

‎tests/ui/crashes/ice-7410.rs‎

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#![no_std]
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#![allow(clippy::if_same_then_else)]
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#![allow(clippy::redundant_pattern_matching)]
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#![allow(clippy::needless_else)]
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use core::panic::PanicInfo;
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‎tests/ui/ifs_same_cond.rs‎

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#![warn(clippy::ifs_same_cond)]
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#![allow(clippy::if_same_then_else, clippy::comparison_chain)] // all empty blocks
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#![allow(clippy::if_same_then_else, clippy::comparison_chain, clippy::needless_else)] // all empty blocks
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fn ifs_same_cond() {
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let a = 0;

‎tests/ui/needless_else.fixed‎

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//@run-rustfix
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#![allow(unused)]
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#![warn(clippy::needless_else)]
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#![allow(clippy::suspicious_else_formatting)]
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macro_rules! mac {
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($test:expr) => {
8+
if $test {
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println!("Test successful!");
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} else {
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}
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};
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}
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fn main() {
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let b = std::hint::black_box(true);
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if b {
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println!("Foobar");
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}
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if b {
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println!("Foobar");
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} else {
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// Do not lint because this comment might be important
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}
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if b {
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println!("Foobar");
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} else
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/* Do not lint because this comment might be important */
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{
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}
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// Do not lint because of the expression
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let _ = if b { 1 } else { 2 };
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// Do not lint because inside a macro
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mac!(b);
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}

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