Honor #[rustfmt::skip::attributes(derive)] attribute

Fixes 5270

Previously, rustfmt only checked the `merge_derives` configuration value
to determine if it should merge_derives. This lead to derives being
merged even when annotated with the `rustfmt::skip` attribute.

Now, rustfmt also checks if derives are explicitly being skipped in the
current context via the `rustfmt::skip` attribute.

src/attr.rs

@@ -389,6 +389,10 @@ impl Rewrite for [ast::Attribute] {
         let mut attrs = self;
         let mut result = String::new();
 
+        // Determine if the source text is annotated with `#[rustfmt::skip::attributes(derive)]`
+        // or `#![rustfmt::skip::attributes(derive)]`
+        let skip_derives = context.skip_context.skip_attribute("derive");
+
         // This is not just a simple map because we need to handle doc comments
         // (where we take as many doc comment attributes as possible) and possibly
         // merging derives into a single attribute.
@@ -431,7 +435,7 @@ impl Rewrite for [ast::Attribute] {
             }
 
             // Handle derives if we will merge them.
-            if context.config.merge_derives() && is_derive(&attrs[0]) {
+            if !skip_derives && context.config.merge_derives() && is_derive(&attrs[0]) {
                 let derives = take_while_with_pred(context, attrs, is_derive);
                 let derive_str = format_derive(derives, shape, context)?;
                 result.push_str(&derive_str);

tests/source/issue-5270/merge_derives_true.rs

@@ -0,0 +1,62 @@
+// rustfmt-merge_derives:true
+
+#[rustfmt::skip::attributes(derive)]
+#[allow(dead_code)]
+#[derive(StructField)]
+#[derive(Clone)]
+struct DoNotMergeDerives {
+    field: String,
+}
+
+#[allow(dead_code)]
+#[derive(StructField)]
+#[rustfmt::skip::attributes(derive)]
+#[derive(Clone)]
+struct DoNotMergeDerivesSkipInMiddle {
+    field: String,
+}
+
+#[allow(dead_code)]
+#[derive(StructField)]
+#[derive(Clone)]
+#[rustfmt::skip::attributes(derive)]
+struct DoNotMergeDerivesSkipAtEnd {
+    field: String,
+}
+
+#[allow(dead_code)]
+#[derive(StructField)]
+#[derive(Clone)]
+struct MergeDerives {
+    field: String,
+}
+
+mod inner_attribute_derive_skip {
+    #![rustfmt::skip::attributes(derive)]
+
+    #[allow(dead_code)]
+    #[derive(StructField)]
+    #[derive(Clone)]
+    struct DoNotMergeDerives {
+        field: String,
+    }
+}
+
+#[rustfmt::skip::attributes(derive)]
+mod outer_attribute_derive_skip {
+    #[allow(dead_code)]
+    #[derive(StructField)]
+    #[derive(Clone)]
+    struct DoNotMergeDerives {
+        field: String,
+    }
+}
+
+mod no_derive_skip {
+    #[allow(dead_code)]
+    #[derive(StructField)]
+    #[derive(Clone)]
+    struct MergeDerives {
+        field: String,
+    }
+}

tests/target/issue-5270/merge_derives_false.rs

@@ -0,0 +1,62 @@
+// rustfmt-merge_derives:false
+
+#[rustfmt::skip::attributes(derive)]
+#[allow(dead_code)]
+#[derive(StructField)]
+#[derive(Clone)]
+struct DoNotMergeDerives {
+    field: String,
+}
+
+#[allow(dead_code)]
+#[derive(StructField)]
+#[rustfmt::skip::attributes(derive)]
+#[derive(Clone)]
+struct DoNotMergeDerivesSkipInMiddle {
+    field: String,
+}
+
+#[allow(dead_code)]
+#[derive(StructField)]
+#[derive(Clone)]
+#[rustfmt::skip::attributes(derive)]
+struct DoNotMergeDerivesSkipAtEnd {
+    field: String,
+}
+
+#[allow(dead_code)]
+#[derive(StructField)]
+#[derive(Clone)]
+struct MergeDerives {
+    field: String,
+}
+
+mod inner_attribute_derive_skip {
+    #![rustfmt::skip::attributes(derive)]
+
+    #[allow(dead_code)]
+    #[derive(StructField)]
+    #[derive(Clone)]
+    struct DoNotMergeDerives {
+        field: String,
+    }
+}
+
+#[rustfmt::skip::attributes(derive)]
+mod outer_attribute_derive_skip {
+    #[allow(dead_code)]
+    #[derive(StructField)]
+    #[derive(Clone)]
+    struct DoNotMergeDerives {
+        field: String,
+    }
+}
+
+mod no_derive_skip {
+    #[allow(dead_code)]
+    #[derive(StructField)]
+    #[derive(Clone)]
+    struct MergeDerives {
+        field: String,
+    }
+}

tests/target/issue-5270/merge_derives_true.rs

@@ -0,0 +1,60 @@
+// rustfmt-merge_derives:true
+
+#[rustfmt::skip::attributes(derive)]
+#[allow(dead_code)]
+#[derive(StructField)]
+#[derive(Clone)]
+struct DoNotMergeDerives {
+    field: String,
+}
+
+#[allow(dead_code)]
+#[derive(StructField)]
+#[rustfmt::skip::attributes(derive)]
+#[derive(Clone)]
+struct DoNotMergeDerivesSkipInMiddle {
+    field: String,
+}
+
+#[allow(dead_code)]
+#[derive(StructField)]
+#[derive(Clone)]
+#[rustfmt::skip::attributes(derive)]
+struct DoNotMergeDerivesSkipAtEnd {
+    field: String,
+}
+
+#[allow(dead_code)]
+#[derive(StructField, Clone)]
+struct MergeDerives {
+    field: String,
+}
+
+mod inner_attribute_derive_skip {
+    #![rustfmt::skip::attributes(derive)]
+
+    #[allow(dead_code)]
+    #[derive(StructField)]
+    #[derive(Clone)]
+    struct DoNotMergeDerives {
+        field: String,
+    }
+}
+
+#[rustfmt::skip::attributes(derive)]
+mod outer_attribute_derive_skip {
+    #[allow(dead_code)]
+    #[derive(StructField)]
+    #[derive(Clone)]
+    struct DoNotMergeDerives {
+        field: String,
+    }
+}
+
+mod no_derive_skip {
+    #[allow(dead_code)]
+    #[derive(StructField, Clone)]
+    struct MergeDerives {
+        field: String,
+    }
+}