Fix idempotency issue when wrapping the last match arm in a block

The issues was related to the interaction between two differnt
configuration options when applied to the last match arm.

* trailing_comma = Never
* match_block_trailing_comma = true

Previously, rustfmt only consider the ``match_block_trailing_comma``
configuration value when wrapping match arms. This lead to rustfmt
adding a trailing comma to all newly wrapped match arms.

Now, rustfmt also considers the ``trailing_comma`` configuration value
when deciding whether or not to add a trailing comma when wrapping the
last match arm in a block.

Author: ytmimi

src/matches.rs

@@ -420,7 +420,10 @@ fn rewrite_match_body(
         let indent_str = shape.indent.to_string_with_newline(context.config);
         let (body_prefix, body_suffix) =
             if context.config.match_arm_blocks() && !context.inside_macro() {
-                let comma = if context.config.match_block_trailing_comma() {
+                let comma_never = context.config.trailing_comma() == SeparatorTactic::Never;
+                let comma = if is_last && comma_never {
+                    ""
+                } else if context.config.match_block_trailing_comma() {
                     ","
                 } else {
                     ""

tests/source/issue-5193/match_block_trailing_comma_false/trailing_comma_always.rs

@@ -0,0 +1,16 @@
+// rustfmt-max_width: 90
+// rustfmt-match_block_trailing_comma: false
+// rustfmt-trailing_comma: Always
+
+fn main() {
+    match FooBar::Foo {
+        FooBar::Foo => unreachable!(),
+        FooBar::Bar => {
+            println!("match_block_trailing_comma: false");
+            println!("trailing_comma: Always");
+        }
+        FooBar::Baz => println!(
+            "Lorem ipsum dolor sit amet, consectetuer adipiscing elit."
+        )
+    }
+}

tests/source/issue-5193/match_block_trailing_comma_false/trailing_comma_never.rs

@@ -0,0 +1,16 @@
+// rustfmt-max_width: 90
+// rustfmt-match_block_trailing_comma: false
+// rustfmt-trailing_comma: Never
+
+fn main() {
+    match FooBar::Foo {
+        FooBar::Foo => unreachable!(),
+        FooBar::Bar => {
+            println!("match_block_trailing_comma: false");
+            println!("trailing_comma: Never");
+        }
+        FooBar::Baz => println!(
+            "Lorem ipsum dolor sit amet, consectetuer adipiscing elit."
+        )
+    }
+}

tests/source/issue-5193/match_block_trailing_comma_false/trailing_comma_vertical.rs

@@ -0,0 +1,16 @@
+// rustfmt-max_width: 90
+// rustfmt-match_block_trailing_comma: false
+// rustfmt-trailing_comma: Vertical
+
+fn main() {
+    match FooBar::Foo {
+        FooBar::Foo => unreachable!(),
+        FooBar::Bar => {
+            println!("match_block_trailing_comma: false");
+            println!("trailing_comma: Vertical");
+        }
+        FooBar::Baz => println!(
+            "Lorem ipsum dolor sit amet, consectetuer adipiscing elit."
+        )
+    }
+}

tests/source/issue-5193/match_block_trailing_comma_true/trailing_comma_always.rs

@@ -0,0 +1,16 @@
+// rustfmt-max_width: 90
+// rustfmt-match_block_trailing_comma: true
+// rustfmt-trailing_comma: Always
+
+fn main() {
+    match FooBar::Foo {
+        FooBar::Foo => unreachable!(),
+        FooBar::Bar => {
+            println!("match_block_trailing_comma: true");
+            println!("trailing_comma: Always");
+        }
+        FooBar::Baz => println!(
+            "Lorem ipsum dolor sit amet, consectetuer adipiscing elit."
+        )
+    }
+}

tests/source/issue-5193/match_block_trailing_comma_true/trailing_comma_never.rs

@@ -0,0 +1,16 @@
+// rustfmt-max_width: 90
+// rustfmt-match_block_trailing_comma: true
+// rustfmt-trailing_comma: Never
+
+fn main() {
+    match FooBar::Foo {
+        FooBar::Foo => unreachable!(),
+        FooBar::Bar => {
+            println!("match_block_trailing_comma: true");
+            println!("trailing_comma: Never");
+        }
+        FooBar::Baz => println!(
+            "Lorem ipsum dolor sit amet, consectetuer adipiscing elit."
+        )
+    }
+}

tests/source/issue-5193/match_block_trailing_comma_true/trailing_comma_vertical.rs

@@ -0,0 +1,16 @@
+// rustfmt-max_width: 90
+// rustfmt-match_block_trailing_comma: true
+// rustfmt-trailing_comma: Vertical
+
+fn main() {
+    match FooBar::Foo {
+        FooBar::Foo => unreachable!(),
+        FooBar::Bar => {
+            println!("match_block_trailing_comma: true");
+            println!("trailing_comma: Vertical");
+        }
+        FooBar::Baz => println!(
+            "Lorem ipsum dolor sit amet, consectetuer adipiscing elit."
+        )
+    }
+}

tests/target/issue-5193/match_block_trailing_comma_false/trailing_comma_always.rs

@@ -0,0 +1,16 @@
+// rustfmt-max_width: 90
+// rustfmt-match_block_trailing_comma: false
+// rustfmt-trailing_comma: Always
+
+fn main() {
+    match FooBar::Foo {
+        FooBar::Foo => unreachable!(),
+        FooBar::Bar => {
+            println!("match_block_trailing_comma: false");
+            println!("trailing_comma: Always");
+        }
+        FooBar::Baz => {
+            println!("Lorem ipsum dolor sit amet, consectetuer adipiscing elit.")
+        }
+    }
+}

tests/target/issue-5193/match_block_trailing_comma_false/trailing_comma_never.rs

@@ -0,0 +1,16 @@
+// rustfmt-max_width: 90
+// rustfmt-match_block_trailing_comma: false
+// rustfmt-trailing_comma: Never
+
+fn main() {
+    match FooBar::Foo {
+        FooBar::Foo => unreachable!(),
+        FooBar::Bar => {
+            println!("match_block_trailing_comma: false");
+            println!("trailing_comma: Never");
+        }
+        FooBar::Baz => {
+            println!("Lorem ipsum dolor sit amet, consectetuer adipiscing elit.")
+        }
+    }
+}

tests/target/issue-5193/match_block_trailing_comma_false/trailing_comma_vertical.rs

@@ -0,0 +1,16 @@
+// rustfmt-max_width: 90
+// rustfmt-match_block_trailing_comma: false
+// rustfmt-trailing_comma: Vertical
+
+fn main() {
+    match FooBar::Foo {
+        FooBar::Foo => unreachable!(),
+        FooBar::Bar => {
+            println!("match_block_trailing_comma: false");
+            println!("trailing_comma: Vertical");
+        }
+        FooBar::Baz => {
+            println!("Lorem ipsum dolor sit amet, consectetuer adipiscing elit.")
+        }
+    }
+}