fix: Avoid incorrect global 'cfg_if' Symbol interning

Fixes #4656

src/lib.rs

@@ -3,6 +3,7 @@
 
 #[macro_use]
 extern crate derive_new;
+#[cfg(test)]
 #[macro_use]
 extern crate lazy_static;
 #[macro_use]

src/modules.rs

@@ -21,10 +21,6 @@
 
 type FileModMap<'ast> = BTreeMap<FileName, Module<'ast>>;
 
-lazy_static! {
-    static ref CFG_IF: Symbol = Symbol::intern("cfg_if");
-}
-
 /// Represents module with its inner attributes.
 #[derive(Debug, Clone)]
 pub(crate) struct Module<'a> {
@@ -480,7 +476,7 @@ fn is_cfg_if(item: &ast::Item) -> bool {
     match item.kind {
         ast::ItemKind::MacCall(ref mac) => {
             if let Some(first_segment) = mac.path.segments.first() {
-                if first_segment.ident.name == *CFG_IF {
+                if first_segment.ident.name == Symbol::intern("cfg_if") {
                     return true;
                 }
             }

src/test/mod.rs

@@ -372,6 +372,44 @@ fn self_tests() {
     );
 }
 
+#[test]
+fn format_files_find_new_files_via_cfg_if() {
+    init_log();
+    run_test_with(&TestSetting::default(), || {
+        // To repro issue-4656, it is necessary that these files are parsed
+        // as a part of the same session (hence this separate test runner).
+        let files = vec![
+            Path::new("tests/source/issue-4656/lib2.rs"),
+            Path::new("tests/source/issue-4656/lib.rs"),
+        ];
+
+        let config = Config::default();
+        let mut session = Session::<io::Stdout>::new(config, None);
+
+        let mut write_result = HashMap::new();
+        for file in files {
+            assert!(file.exists());
+            let result = session.format(Input::File(file.into())).unwrap();
+            assert!(!session.has_formatting_errors());
+            assert!(!result.has_warnings());
+            let mut source_file = SourceFile::new();
+            mem::swap(&mut session.source_file, &mut source_file);
+
+            for (filename, text) in source_file {
+                if let FileName::Real(ref filename) = filename {
+                    write_result.insert(filename.to_owned(), text);
+                }
+            }
+        }
+        assert_eq!(
+            3,
+            write_result.len(),
+            "Should have uncovered an extra file (format_me_please.rs) via lib.rs"
+        );
+        assert!(handle_result(write_result, None).is_ok());
+    });
+}
+
 #[test]
 fn stdin_formatting_smoke_test() {
     init_log();

tests/source/issue-4656/format_me_please.rs

@@ -0,0 +1,2 @@
+
+pub fn     hello(   )  {     }

tests/source/issue-4656/lib.rs

@@ -0,0 +1,7 @@
+extern crate cfg_if;
+
+cfg_if::cfg_if! {
+    if #[cfg(target_family = "unix")] {
+        mod format_me_please;
+    }
+}

tests/source/issue-4656/lib2.rs

@@ -0,0 +1,3 @@
+its_a_macro! {
+    // Contents
+}

tests/target/issue-4656/format_me_please.rs

@@ -0,0 +1 @@
+pub fn hello() {}

tests/target/issue-4656/lib.rs

@@ -0,0 +1,7 @@
+extern crate cfg_if;
+
+cfg_if::cfg_if! {
+    if #[cfg(target_family = "unix")] {
+        mod format_me_please;
+    }
+}

tests/target/issue-4656/lib2.rs

@@ -0,0 +1,3 @@
+its_a_macro! {
+    // Contents
+}