Add config option generated_file_header_size

Configurations.md

@@ -1050,15 +1050,23 @@ Max width for code snippets included in doc comments. Only used if [`format_code
 
 ## `format_generated_files`
 
-Format generated files. A file is considered generated
-if any of the first five lines contain a `@generated` comment marker.
+Format generated files. A file is considered generated if any of the first several lines contain a `@generated` comment marker. The number of lines to check is configured by `generated_file_header_size`.
+
 By default, generated files are reformatted, i. e. `@generated` marker is ignored.
 This option is currently ignored for stdin (`@generated` in stdin is ignored.)
 
 - **Default value**: `true`
 - **Possible values**: `true`, `false`
 - **Stable**: No (tracking issue: [#5080](https://github.com/rust-lang/rustfmt/issues/5080))
 
+## `generated_file_header_size`
+
+Number of lines to check for a `@generated` pragma header when `format_generated_files` is enabled. When `format_generated_files` is disabled, this option has no effect.
+
+- **Default value**: `5`
+- **Possible values**: any positive integer
+- **Stable**: No (tracking issue: [#5080](https://github.com/rust-lang/rustfmt/issues/5080))
+
 ## `format_macro_matchers`
 
 Format the metavariable matching patterns in macros.

src/config/mod.rs

@@ -148,6 +148,8 @@ create_config! {
         "Write an item and its attribute on the same line \
         if their combined width is below a threshold";
     format_generated_files: bool, true, false, "Format generated files";
+    generated_file_header_size: usize, 5, false, "Number of lines to check for a `@generated` \
+        marker when `format_generated_files` is enabled";
 
     // Options that can change the source code beyond whitespace/blocks (somewhat linty things)
     merge_derives: bool, true, true, "Merge multiple `#[derive(...)]` into a single one";
@@ -667,6 +669,7 @@ edition = "2015"
 version = "One"
 inline_attribute_width = 0
 format_generated_files = true
+generated_file_header_size = 5
 merge_derives = true
 use_try_shorthand = false
 use_field_init_shorthand = false

src/formatting.rs

@@ -82,7 +82,7 @@ fn should_skip_module<T: FormatHandler>(
         let source_file = context.parse_session.span_to_file_contents(module.span);
         let src = source_file.src.as_ref().expect("SourceFile without src");
 
-        if is_generated_file(src) {
+        if is_generated_file(src, config.generated_file_header_size()) {
             return true;
         }
     }

src/formatting/generated.rs

@@ -1,7 +1,7 @@
 /// Returns `true` if the given span is a part of generated files.
-pub(super) fn is_generated_file(original_snippet: &str) -> bool {
+pub(super) fn is_generated_file(original_snippet: &str, header_size: usize) -> bool {
     original_snippet
         .lines()
-        .take(5) // looking for marker only in the beginning of the file
+        .take(header_size) // looking for marker only in the beginning of the file
         .any(|line| line.contains("@generated"))
 }