Add ignore_missing_submod config option

Author: tanzaku

Configurations.md

@@ -1288,6 +1288,14 @@ If you want to ignore every file under the directory where you put your rustfmt.
 ignore = ["/"]
 ```
 
+## `ignore_missing_submod`
+
+Ignore missing submodule error.
+
+- **Default value**: `false`
+- **Possible values**: `true`, `false`
+- **Stable**: Yes
+
 ## `imports_indent`
 
 Indent style of imports

src/config/mod.rs

@@ -173,6 +173,7 @@ create_config! {
          or they are left with trailing whitespaces";
     ignore: IgnoreList, IgnoreList::default(), false,
         "Skip formatting the specified files and directories";
+    ignore_missing_submod: bool, false, true, "Ignore missing submodule error";
 
     // Not user-facing
     verbose: Verbosity, Verbosity::Normal, false, "How much to information to emit to the user";
@@ -681,6 +682,7 @@ hide_parse_errors = false
 error_on_line_overflow = false
 error_on_unformatted = false
 ignore = []
+ignore_missing_submod = false
 emit_mode = "Files"
 make_backup = false
 "#,

src/formatting.rs

@@ -135,6 +135,7 @@ fn format_project<T: FormatHandler>(
         &context.parse_session,
         directory_ownership.unwrap_or(DirectoryOwnership::UnownedViaBlock),
         !input_is_stdin && !config.skip_children(),
+        config.ignore_missing_submod(),
     )
     .visit_crate(&krate)?
     .into_iter()

src/modules.rs

@@ -61,6 +61,7 @@ pub(crate) struct ModResolver<'ast, 'sess> {
     directory: Directory,
     file_map: FileModMap<'ast>,
     recursive: bool,
+    ignore_missing_submod: bool,
 }
 
 /// Represents errors while trying to resolve modules.
@@ -104,6 +105,7 @@ impl<'ast, 'sess, 'c> ModResolver<'ast, 'sess> {
         parse_sess: &'sess ParseSess,
         directory_ownership: DirectoryOwnership,
         recursive: bool,
+        ignore_missing_submod: bool,
     ) -> Self {
         ModResolver {
             directory: Directory {
@@ -113,6 +115,7 @@ impl<'ast, 'sess, 'c> ModResolver<'ast, 'sess> {
             file_map: BTreeMap::new(),
             parse_sess,
             recursive,
+            ignore_missing_submod,
         }
     }
 
@@ -248,6 +251,14 @@ impl<'ast, 'sess, 'c> ModResolver<'ast, 'sess> {
             // mod foo;
             // Look for an extern file.
             self.find_external_module(item.ident, &item.attrs, sub_mod)
+                .or_else(|err| match err.kind {
+                    ModuleResolutionErrorKind::NotFound { file: _ }
+                        if self.ignore_missing_submod =>
+                    {
+                        Ok(None)
+                    }
+                    _ => Err(err),
+                })
         } else {
             // An internal module (`mod foo { /* ... */ }`);
             Ok(Some(SubModKind::Internal(item)))

tests/config/issue-5609.toml

@@ -0,0 +1 @@
+ignore_missing_submod = true

tests/source/issue-5609.rs

@@ -0,0 +1,7 @@
+// rustfmt-config: issue-5609.toml
+
+mod missing_submod;
+
+fn test() {
+
+}

tests/target/issue-5609.rs

@@ -0,0 +1,5 @@
+// rustfmt-config: issue-5609.toml
+
+mod missing_submod;
+
+fn test() {}