Add multiline_{closure,match_arm}_forces_block

multiline_closure_forces_block = false (default):
    result.and_then(|maybe_value| match maybe_value {
        None => ...,
        Some(value) => ...,
    })

multiline_closure_forces_block = true:
    result.and_then(|maybe_value| {
        match maybe_value {
            None => ...,
            Some(value) => ...,
        }
    })

multiline_match_arm_forces_block = false (default):
    match lorem {
        None => if ipsum {
            println!("Hello World");
        },
        Some(dolor) => ...,
    }

multiline_match_arm_forces_block = true:
    match lorem {
        None => {
            if ipsum {
                println!("Hello World");
            }
        }
        Some(dolor) => ...,
    }

Configurations.md

@@ -1265,6 +1265,64 @@ Maximum width of each line
 
 See also [`error_on_line_overflow`](#error_on_line_overflow).
 
+## `multiline_closure_forces_block`
+
+Force multiline closure bodies to be wrapped in a block
+
+- **Default value**: `false`
+- **Possible values**: `false`, `true`
+
+#### `false`:
+
+```rust
+result.and_then(|maybe_value| match maybe_value {
+    None => ...,
+    Some(value) => ...,
+})
+```
+
+#### `true`:
+
+```rust
+result.and_then(|maybe_value| {
+    match maybe_value {
+        None => ...,
+        Some(value) => ...,
+    }
+})
+```
+
+## `multiline_match_arm_forces_block`
+
+Force multiline match arm bodies to be wrapped in a block
+
+- **Default value**: `false`
+- **Possible values**: `false`, `true`
+
+#### `false`:
+
+```rust
+match lorem {
+    None => if ipsum {
+        println!("Hello World");
+    },
+    Some(dolor) => ...,
+}
+```
+
+#### `true`:
+
+```rust
+match lorem {
+    None => {
+        if ipsum {
+            println!("Hello World");
+        }
+    }
+    Some(dolor) => ...,
+}
+```
+
 ## `newline_style`
 
 Unix or Windows line endings

src/config.rs

@@ -615,6 +615,10 @@ create_config! {
         "Try to put attributes on the same line as fields.";
     attributes_on_same_line_as_variant: bool, true,
         "Try to put attributes on the same line as variants in enum declarations.";
+    multiline_closure_forces_block: bool, false,
+        "Force multiline closure bodies to be wrapped in a block";
+    multiline_match_arm_forces_block: bool, false,
+        "Force multiline match arm bodies to be wrapped in a block";
 }
 
 #[cfg(test)]

src/expr.rs

@@ -690,6 +690,13 @@ fn rewrite_closure_expr(
     if classify::expr_requires_semi_to_be_stmt(left_most_sub_expr(expr)) {
         rewrite = and_one_line(rewrite);
     }
+    rewrite = rewrite.and_then(|rw| {
+        if context.config.multiline_closure_forces_block() && rw.contains('\n') {
+            None
+        } else {
+            Some(rw)
+        }
+    });
     rewrite.map(|rw| format!("{} {}", prefix, rw))
 }
 
@@ -1690,12 +1697,20 @@ fn flatten_arm_body<'a>(context: &'a RewriteContext, body: &'a ast::Expr) -> (bo
             if !is_unsafe_block(block) && is_simple_block(block, context.codemap) =>
         {
             if let ast::StmtKind::Expr(ref expr) = block.stmts[0].node {
-                (expr.can_be_overflowed(context, 1), &**expr)
+                (
+                    !context.config.multiline_match_arm_forces_block() &&
+                        expr.can_be_overflowed(context, 1),
+                    &**expr,
+                )
             } else {
                 (false, &*body)
             }
         }
-        _ => (body.can_be_overflowed(context, 1), &*body),
+        _ => (
+            !context.config.multiline_match_arm_forces_block() &&
+                body.can_be_overflowed(context, 1),
+            &*body,
+        ),
     }
 }
 

tests/source/configs-multiline_closure_forces_block-false.rs

@@ -0,0 +1,11 @@
+// rustfmt-multiline_closure_forces_block: false
+// Option forces multiline closure bodies to be wrapped in a block
+
+fn main() {
+    result.and_then(|maybe_value| {
+        match maybe_value {
+            None => Err("oops"),
+            Some(value) => Ok(1),
+        }
+    });
+}

tests/source/configs-multiline_closure_forces_block-true.rs

@@ -0,0 +1,9 @@
+// rustfmt-multiline_closure_forces_block: true
+// Option forces multiline closure bodies to be wrapped in a block
+
+fn main() {
+    result.and_then(|maybe_value| match maybe_value {
+        None => Err("oops"),
+        Some(value) => Ok(1),
+    });
+}

tests/source/configs-multiline_match_arm_forces_block-false.rs

@@ -0,0 +1,13 @@
+// rustfmt-multiline_match_arm_forces_block: false
+// Option forces multiline match arm bodies to be wrapped in a block
+
+fn main() {
+    match lorem {
+        Lorem::Ipsum => {
+            if ipsum {
+                println!("dolor");
+            }
+        }
+        Lorem::Dolor => println!("amet"),
+    }
+}

tests/source/configs-multiline_match_arm_forces_block-true.rs

@@ -0,0 +1,11 @@
+// rustfmt-multiline_match_arm_forces_block: true
+// Option forces multiline match arm bodies to be wrapped in a block
+
+fn main() {
+    match lorem {
+        Lorem::Ipsum => if ipsum {
+            println!("dolor");
+        },
+        Lorem::Dolor => println!("amet"),
+    }
+}

tests/target/configs-multiline_closure_forces_block-false.rs

@@ -0,0 +1,9 @@
+// rustfmt-multiline_closure_forces_block: false
+// Option forces multiline closure bodies to be wrapped in a block
+
+fn main() {
+    result.and_then(|maybe_value| match maybe_value {
+        None => Err("oops"),
+        Some(value) => Ok(1),
+    });
+}

tests/target/configs-multiline_closure_forces_block-true.rs

@@ -0,0 +1,11 @@
+// rustfmt-multiline_closure_forces_block: true
+// Option forces multiline closure bodies to be wrapped in a block
+
+fn main() {
+    result.and_then(|maybe_value| {
+        match maybe_value {
+            None => Err("oops"),
+            Some(value) => Ok(1),
+        }
+    });
+}

tests/target/configs-multiline_match_arm_forces_block-false.rs

@@ -0,0 +1,11 @@
+// rustfmt-multiline_match_arm_forces_block: false
+// Option forces multiline match arm bodies to be wrapped in a block
+
+fn main() {
+    match lorem {
+        Lorem::Ipsum => if ipsum {
+            println!("dolor");
+        },
+        Lorem::Dolor => println!("amet"),
+    }
+}

tests/target/configs-multiline_match_arm_forces_block-true.rs

@@ -0,0 +1,13 @@
+// rustfmt-multiline_match_arm_forces_block: true
+// Option forces multiline match arm bodies to be wrapped in a block
+
+fn main() {
+    match lorem {
+        Lorem::Ipsum => {
+            if ipsum {
+                println!("dolor");
+            }
+        }
+        Lorem::Dolor => println!("amet"),
+    }
+}