Fix Double trailing Comma (issue 4926)

I found a test case where an additional trailing comma was added in
the event that struct fields were formatted on a single line.

This is not the entended behavior so now we first check if a trailing
comma exists before trying to add one before the ".."

Author: ytmimi

src/expr.rs

@@ -1585,7 +1585,11 @@ fn rewrite_struct_lit<'a>(
                         format!("{},\n{}..", rewritten_fields, indentation)
                     }
                 } else {
-                    format!("{}, ..", rewritten_fields)
+                    if rewritten_fields.ends_with(",") {
+                        format!("{} ..", rewritten_fields)
+                    } else {
+                        format!("{}, ..", rewritten_fields)
+                    }
                 }
             }
             _ => rewritten_fields,

tests/source/issue-4926/enum_struct_field.rs

@@ -0,0 +1,35 @@
+// rustfmt-struct_field_align_threshold: 30
+// rustfmt-enum_discrim_align_threshold: 30
+// rustfmt-imports_layout: HorizontalVertical
+
+#[derive(Default)]
+struct InnerStructA { bbbbbbbbb: i32, cccccccc: i32 }
+
+enum SomeEnumNamedD {
+    E(InnerStructA),
+    F {
+        ggggggggggggggggggggggggg: bool,
+        h: bool,
+    }
+}
+
+impl SomeEnumNamedD {
+    fn f_variant() -> Self {
+        Self::F { ggggggggggggggggggggggggg: true, h: true }
+    }
+}
+
+fn main() {
+    let kkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkk = SomeEnumNamedD::f_variant();
+    let something_we_care_about = matches!(
+        kkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkk,
+        SomeEnumNamedD::F {
+            ggggggggggggggggggggggggg: true,
+            ..
+        }
+    );
+
+    if something_we_care_about {
+        println!("Yup it happened");
+    }
+}

tests/target/issue-4926/enum_struct_field.rs

@@ -0,0 +1,40 @@
+// rustfmt-struct_field_align_threshold: 30
+// rustfmt-enum_discrim_align_threshold: 30
+// rustfmt-imports_layout: HorizontalVertical
+
+#[derive(Default)]
+struct InnerStructA {
+    bbbbbbbbb: i32,
+    cccccccc:  i32,
+}
+
+enum SomeEnumNamedD {
+    E(InnerStructA),
+    F {
+        ggggggggggggggggggggggggg: bool,
+        h:                         bool,
+    },
+}
+
+impl SomeEnumNamedD {
+    fn f_variant() -> Self {
+        Self::F {
+            ggggggggggggggggggggggggg: true,
+            h:                         true,
+        }
+    }
+}
+
+fn main() {
+    let kkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkk = SomeEnumNamedD::f_variant();
+    let something_we_care_about = matches!(
+        kkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkk,
+        SomeEnumNamedD::F {
+            ggggggggggggggggggggggggg: true, ..
+        }
+    );
+
+    if something_we_care_about {
+        println!("Yup it happened");
+    }
+}