add `semicolon_outside_block_if_singleline` lint

CHANGELOG.md

@@ -4884,6 +4884,7 @@ Released 2018-09-13
 [`semicolon_if_nothing_returned`]: https://rust-lang.github.io/rust-clippy/master/index.html#semicolon_if_nothing_returned
 [`semicolon_inside_block`]: https://rust-lang.github.io/rust-clippy/master/index.html#semicolon_inside_block
 [`semicolon_outside_block`]: https://rust-lang.github.io/rust-clippy/master/index.html#semicolon_outside_block
+[`semicolon_outside_block_if_singleline`]: https://rust-lang.github.io/rust-clippy/master/index.html#semicolon_outside_block_if_singleline
 [`separated_literal_suffix`]: https://rust-lang.github.io/rust-clippy/master/index.html#separated_literal_suffix
 [`serde_api_misuse`]: https://rust-lang.github.io/rust-clippy/master/index.html#serde_api_misuse
 [`shadow_reuse`]: https://rust-lang.github.io/rust-clippy/master/index.html#shadow_reuse

clippy_lints/src/declared_lints.rs

@@ -546,6 +546,7 @@ pub(crate) static LINTS: &[&crate::LintInfo] = &[
     crate::self_named_constructors::SELF_NAMED_CONSTRUCTORS_INFO,
     crate::semicolon_block::SEMICOLON_INSIDE_BLOCK_INFO,
     crate::semicolon_block::SEMICOLON_OUTSIDE_BLOCK_INFO,
+    crate::semicolon_block::SEMICOLON_OUTSIDE_BLOCK_IF_SINGLELINE_INFO,
     crate::semicolon_if_nothing_returned::SEMICOLON_IF_NOTHING_RETURNED_INFO,
     crate::serde_api::SERDE_API_MISUSE_INFO,
     crate::shadow::SHADOW_REUSE_INFO,

clippy_lints/src/semicolon_block.rs

@@ -64,7 +64,48 @@ declare_clippy_lint! {
     restriction,
     "add a semicolon outside the block"
 }
-declare_lint_pass!(SemicolonBlock => [SEMICOLON_INSIDE_BLOCK, SEMICOLON_OUTSIDE_BLOCK]);
+declare_clippy_lint! {
+    /// ### What it does
+    ///
+    /// Suggests moving the semicolon from a block's final expression outside of
+    /// the block if it's singleline, and inside the block if it's multiline.
+    ///
+    /// ### Why is this bad?
+    ///
+    /// Some may prefer if the  semicolon is outside if a block is only one
+    /// expression, as this allows rustfmt to make it singleline. In the case that
+    /// it isn't, it should be inside.
+    /// Take a look at both `semicolon_inside_block` and `semicolon_outside_block` for alternatives.
+    ///
+    /// ### Example
+    ///
+    /// ```rust
+    /// # fn f(_: u32) {}
+    /// # let x = 0;
+    /// unsafe { f(x); }
+    /// 
+    /// unsafe {
+    ///     let x = 1;
+    ///     f(x)
+    /// };
+    /// ```
+    /// Use instead:
+    /// ```rust
+    /// # fn f(_: u32) {}
+    /// # let x = 0;
+    /// unsafe { f(x) };
+    /// 
+    /// unsafe {
+    ///     let x = 1;
+    ///     f(x);
+    /// }
+    /// ```
+    #[clippy::version = "1.68.0"]
+    pub SEMICOLON_OUTSIDE_BLOCK_IF_SINGLELINE,
+    restriction,
+    "add a semicolon inside the block if it's singleline, otherwise outside"
+}
+declare_lint_pass!(SemicolonBlock => [SEMICOLON_INSIDE_BLOCK, SEMICOLON_OUTSIDE_BLOCK, SEMICOLON_OUTSIDE_BLOCK_IF_SINGLELINE]);
 
 impl LateLintPass<'_> for SemicolonBlock {
     fn check_stmt(&mut self, cx: &LateContext<'_>, stmt: &Stmt<'_>) {
@@ -98,6 +139,8 @@ fn semicolon_inside_block(cx: &LateContext<'_>, block: &Block<'_>, tail: &Expr<'
     let insert_span = tail.span.source_callsite().shrink_to_hi();
     let remove_span = semi_span.with_lo(block.span.hi());
 
+    check_semicolon_outside_block_if_singleline(cx, block, remove_span, insert_span, true, "inside");
+
     span_lint_and_then(
         cx,
         SEMICOLON_INSIDE_BLOCK,
@@ -120,6 +163,8 @@ fn semicolon_outside_block(cx: &LateContext<'_>, block: &Block<'_>, tail_stmt_ex
     let semi_span = cx.sess().source_map().stmt_span(semi_span, block.span);
     let remove_span = semi_span.with_lo(tail_stmt_expr.span.source_callsite().hi());
 
+    check_semicolon_outside_block_if_singleline(cx, block, remove_span, insert_span, false, "outside");
+
     span_lint_and_then(
         cx,
         SEMICOLON_OUTSIDE_BLOCK,
@@ -135,3 +180,48 @@ fn semicolon_outside_block(cx: &LateContext<'_>, block: &Block<'_>, tail_stmt_ex
         },
     );
 }
+
+fn check_semicolon_outside_block_if_singleline(
+    cx: &LateContext<'_>,
+    block: &Block<'_>,
+    remove_span: Span,
+    insert_span: Span,
+    inequality: bool,
+    ty: &str,
+) {
+    let remove_line = cx
+        .sess()
+        .source_map()
+        .lookup_line(remove_span.lo())
+        .expect("failed to get `remove_span`'s line")
+        .line;
+    let insert_line = cx
+        .sess()
+        .source_map()
+        .lookup_line(insert_span.lo())
+        .expect("failed to get `insert_span`'s line")
+        .line;
+
+    let eq = if inequality {
+        remove_line != insert_line
+    } else {
+        remove_line == insert_line
+    };
+
+    if eq {
+        span_lint_and_then(
+            cx,
+            SEMICOLON_OUTSIDE_BLOCK_IF_SINGLELINE,
+            block.span,
+            &format!("consider moving the `;` {ty} the block for consistent formatting"),
+            |diag| {
+                multispan_sugg_with_applicability(
+                    diag,
+                    "put the `;` here",
+                    Applicability::MachineApplicable,
+                    [(remove_span, String::new()), (insert_span, ";".to_owned())],
+                );
+            },
+        );
+    }
+}

tests/ui/semicolon_outside_block_if_singleline.fixed

@@ -0,0 +1,85 @@
+// run-rustfix
+#![allow(
+    unused,
+    clippy::unused_unit,
+    clippy::unnecessary_operation,
+    clippy::no_effect,
+    clippy::single_element_loop
+)]
+#![warn(clippy::semicolon_outside_block_if_singleline)]
+
+macro_rules! m {
+    (()) => {
+        ()
+    };
+    (0) => {{
+        0
+    };};
+    (1) => {{
+        1;
+    }};
+    (2) => {{
+        2;
+    }};
+}
+
+fn unit_fn_block() {
+    ()
+}
+
+#[rustfmt::skip]
+fn main() {
+    { unit_fn_block() }
+    unsafe { unit_fn_block() }
+
+    {
+        unit_fn_block()
+    }
+
+    { unit_fn_block() };
+    unsafe { unit_fn_block() };
+
+    { unit_fn_block() };
+    unsafe { unit_fn_block() };
+
+    { unit_fn_block(); };
+    unsafe { unit_fn_block(); };
+
+    {
+        unit_fn_block();
+        unit_fn_block();
+    }
+    {
+        unit_fn_block();
+        unit_fn_block();
+    }
+    {
+        unit_fn_block();
+        unit_fn_block();
+    };
+
+    { m!(()) };
+    { m!(()) };
+    { m!(()); };
+    m!(0);
+    m!(1);
+    m!(2);
+
+    for _ in [()] {
+        unit_fn_block();
+    }
+    for _ in [()] {
+        unit_fn_block()
+    }
+
+    let _d = || {
+        unit_fn_block();
+    };
+    let _d = || {
+        unit_fn_block()
+    };
+
+    { unit_fn_block(); };
+
+    unit_fn_block()
+}

tests/ui/semicolon_outside_block_if_singleline.rs

@@ -0,0 +1,85 @@
+// run-rustfix
+#![allow(
+    unused,
+    clippy::unused_unit,
+    clippy::unnecessary_operation,
+    clippy::no_effect,
+    clippy::single_element_loop
+)]
+#![warn(clippy::semicolon_outside_block_if_singleline)]
+
+macro_rules! m {
+    (()) => {
+        ()
+    };
+    (0) => {{
+        0
+    };};
+    (1) => {{
+        1;
+    }};
+    (2) => {{
+        2;
+    }};
+}
+
+fn unit_fn_block() {
+    ()
+}
+
+#[rustfmt::skip]
+fn main() {
+    { unit_fn_block() }
+    unsafe { unit_fn_block() }
+
+    {
+        unit_fn_block()
+    }
+
+    { unit_fn_block() };
+    unsafe { unit_fn_block() };
+
+    { unit_fn_block(); }
+    unsafe { unit_fn_block(); }
+
+    { unit_fn_block(); };
+    unsafe { unit_fn_block(); };
+
+    {
+        unit_fn_block();
+        unit_fn_block()
+    };
+    {
+        unit_fn_block();
+        unit_fn_block();
+    }
+    {
+        unit_fn_block();
+        unit_fn_block();
+    };
+
+    { m!(()) };
+    { m!(()); }
+    { m!(()); };
+    m!(0);
+    m!(1);
+    m!(2);
+
+    for _ in [()] {
+        unit_fn_block();
+    }
+    for _ in [()] {
+        unit_fn_block()
+    }
+
+    let _d = || {
+        unit_fn_block();
+    };
+    let _d = || {
+        unit_fn_block()
+    };
+
+    { unit_fn_block(); };
+
+    unit_fn_block()
+}

tests/ui/semicolon_outside_block_if_singleline.stderr

@@ -0,0 +1,54 @@
+error: consider moving the `;` outside the block for consistent formatting
+  --> $DIR/semicolon_outside_block_if_singleline.rs:42:5
+   |
+LL |     { unit_fn_block(); }
+   |     ^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: `-D clippy::semicolon-outside-block-if-singleline` implied by `-D warnings`
+help: put the `;` here
+   |
+LL -     { unit_fn_block(); }
+LL +     { unit_fn_block() };
+   |
+
+error: consider moving the `;` outside the block for consistent formatting
+  --> $DIR/semicolon_outside_block_if_singleline.rs:43:5
+   |
+LL |     unsafe { unit_fn_block(); }
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+help: put the `;` here
+   |
+LL -     unsafe { unit_fn_block(); }
+LL +     unsafe { unit_fn_block() };
+   |
+
+error: consider moving the `;` inside the block for consistent formatting
+  --> $DIR/semicolon_outside_block_if_singleline.rs:48:5
+   |
+LL | /     {
+LL | |         unit_fn_block();
+LL | |         unit_fn_block()
+LL | |     };
+   | |_____^
+   |
+help: put the `;` here
+   |
+LL ~         unit_fn_block();
+LL ~     }
+   |
+
+error: consider moving the `;` outside the block for consistent formatting
+  --> $DIR/semicolon_outside_block_if_singleline.rs:62:5
+   |
+LL |     { m!(()); }
+   |     ^^^^^^^^^^^
+   |
+help: put the `;` here
+   |
+LL -     { m!(()); }
+LL +     { m!(()) };
+   |
+
+error: aborting due to 4 previous errors
+