Add tests

Author: tanzaku

tests/rustfmt/main.rs

@@ -1,8 +1,8 @@
 //! Integration tests for rustfmt.
 
 use std::env;
-use std::fs::remove_file;
-use std::path::Path;
+use std::fs::{read_to_string, remove_file};
+use std::path::{Path, PathBuf};
 use std::process::Command;
 
 use rustfmt_config_proc_macro::rustfmt_only_ci_test;
@@ -200,3 +200,30 @@ fn rustfmt_emits_error_when_control_brace_style_is_always_next_line() {
     let (_stdout, stderr) = rustfmt(&args);
     assert!(!stderr.contains("error[internal]: left behind trailing whitespace"))
 }
+
+#[test]
+fn ignore_missing_sub_mod_false() {
+    // Ensure that missing submodules cause module not found errors when trying to
+    // resolve submodules with `skip_children=false` and `ignore_missing_submod=false`
+    let args = [
+        "--config=skip_children=false,ignore_missing_submod=false",
+        "tests/source/issue-5609.rs",
+    ];
+    let (_stdout, stderr) = rustfmt(&args);
+    // Module resolution fails because we're unable to find `missing_submod.rs`
+    assert!(stderr.contains("missing_submod.rs does not exist"))
+}
+
+#[test]
+fn ignore_missing_sub_mod_true() {
+    // Ensure that missing submodules don't cause module not found errors when trying to
+    // resolve submodules with `skip_children=false` and `ignore_missing_submod=true`.
+    let args = [
+        "--emit=stdout",
+        "--config=skip_children=false,ignore_missing_submod=true",
+        "tests/source/issue-5609.rs",
+    ];
+    let (stdout, _stderr) = rustfmt(&args);
+    let target = read_to_string(PathBuf::from("tests/target/issue-5609.rs")).unwrap();
+    assert!(stdout.ends_with(&target));
+}