Implement preserve mode for trailing-semicolon

Author: compiler-errors

Configurations.md

@@ -2780,20 +2780,32 @@ See also: [`match_block_trailing_comma`](#match_block_trailing_comma).
 
 Add trailing semicolon after break, continue and return
 
-- **Default value**: `true`
-- **Possible values**: `true`, `false`
+- **Default value**: `preserve`
+- **Possible values**: `always`, `never`, `preserve`
 - **Stable**: No (tracking issue: [#3378](https://github.com/rust-lang/rustfmt/issues/3378))
 
-#### `true` (default):
+#### `always` (default):
 ```rust
 fn foo() -> usize {
     return 0;
 }
 ```
 
-#### `false`:
+#### `never`:
+```rust
+fn foo() -> usize {
+    return 0
+}
+```
+
+
+#### `preserve`:
 ```rust
 fn foo() -> usize {
+    return 0;
+}
+
+fn bar() -> usize {
     return 0
 }
 ```

src/config/mod.rs

@@ -135,7 +135,7 @@ create_config! {
     brace_style: BraceStyle, BraceStyle::SameLineWhere, false, "Brace style for items";
     control_brace_style: ControlBraceStyle, ControlBraceStyle::AlwaysSameLine, false,
         "Brace style for control flow constructs";
-    trailing_semicolon: bool, true, false,
+    trailing_semicolon: TrailingSemicolon, TrailingSemicolon::Preserve, false,
         "Add trailing semicolon after break, continue and return";
     trailing_comma: SeparatorTactic, SeparatorTactic::Vertical, false,
         "How to handle trailing commas for lists";
@@ -673,7 +673,7 @@ force_multiline_blocks = false
 fn_params_layout = "Tall"
 brace_style = "SameLineWhere"
 control_brace_style = "AlwaysSameLine"
-trailing_semicolon = true
+trailing_semicolon = preserve
 trailing_comma = "Vertical"
 match_block_trailing_comma = false
 blank_lines_upper_bound = 1

src/config/options.rs

@@ -49,6 +49,13 @@ pub enum ControlBraceStyle {
     AlwaysNextLine,
 }
 
+#[config_type]
+pub enum TrailingSemicolon {
+    Always,
+    Never,
+    Preserve,
+}
+
 #[config_type]
 /// How to indent.
 pub enum IndentStyle {

src/utils.rs

@@ -10,7 +10,7 @@ use rustc_span::{sym, symbol, BytePos, LocalExpnId, Span, Symbol, SyntaxContext}
 use unicode_width::UnicodeWidthStr;
 
 use crate::comment::{filter_normal_code, CharClasses, FullCodeCharKind, LineClasses};
-use crate::config::{Config, Version};
+use crate::config::{Config, TrailingSemicolon, Version};
 use crate::rewrite::RewriteContext;
 use crate::shape::{Indent, Shape};
 
@@ -273,15 +273,18 @@ pub(crate) fn contains_skip(attrs: &[Attribute]) -> bool {
 #[inline]
 pub(crate) fn semicolon_for_expr(context: &RewriteContext<'_>, expr: &ast::Expr) -> bool {
     // Never try to insert semicolons on expressions when we're inside
-    // a macro definition - this can prevent the macro from compiling
+    // a macro definition - this  can prevent the macro from compiling
     // when used in expression position
     if context.is_macro_def {
         return false;
     }
 
     match expr.kind {
         ast::ExprKind::Ret(..) | ast::ExprKind::Continue(..) | ast::ExprKind::Break(..) => {
-            context.config.trailing_semicolon()
+            match context.config.trailing_semicolon() {
+                TrailingSemicolon::Always => true,
+                TrailingSemicolon::Never | TrailingSemicolon::Preserve => false,
+            }
         }
         _ => false,
     }
@@ -301,7 +304,14 @@ pub(crate) fn semicolon_for_stmt(
             ast::ExprKind::Break(..) | ast::ExprKind::Continue(..) | ast::ExprKind::Ret(..) => {
                 // The only time we can skip the semi-colon is if the config option is set to false
                 // **and** this is the last expr (even though any following exprs are unreachable)
-                context.config.trailing_semicolon() || !is_last_expr
+                if !is_last_expr {
+                    true
+                } else {
+                    match context.config.trailing_semicolon() {
+                        TrailingSemicolon::Always | TrailingSemicolon::Preserve => true,
+                        TrailingSemicolon::Never => false,
+                    }
+                }
             }
             _ => true,
         },

tests/target/configs/trailing_semicolon/true.rs renamed to tests/target/configs/trailing_semicolon/always.rs

@@ -1,4 +1,4 @@
-// rustfmt-trailing_semicolon: true
+// rustfmt-trailing_semicolon: always
 
 #![feature(loop_break_value)]
 

tests/target/configs/trailing_semicolon/false.rs renamed to tests/target/configs/trailing_semicolon/never.rs

@@ -1,4 +1,4 @@
-// rustfmt-trailing_semicolon: false
+// rustfmt-trailing_semicolon: never
 
 #![feature(loop_break_value)]
 

tests/target/configs/trailing_semicolon/preserve.rs

@@ -0,0 +1,49 @@
+// rustfmt-trailing_semicolon: never
+
+#![feature(loop_break_value)]
+
+fn main() {
+    'a: loop {
+        break 'a
+    }
+
+    let mut done = false;
+    'b: while !done {
+        done = true;
+        continue 'b
+    }
+
+    let x = loop {
+        break 5
+    };
+
+    let x = 'c: loop {
+        break 'c 5
+    };
+
+    'a: loop {
+        break 'a;
+    }
+
+    let mut done = false;
+    'b: while !done {
+        done = true;
+        continue 'b;
+    }
+
+    let x = loop {
+        break 5;
+    };
+
+    let x = 'c: loop {
+        break 'c 5;
+    };
+}
+
+fn foo() -> usize {
+    return 0
+}
+
+fn bar() -> usize {
+    return 0;
+}

tests/target/issue-5797/retain_trailing_semicolon.rs

@@ -1,4 +1,4 @@
-// rustfmt-trailing_semicolon: false
+// rustfmt-trailing_semicolon: never
 
 fn foo() {}
 fn main() {