Skip all cargo fix that tends to write to registry cache.

src/cargo/ops/fix.rs

@@ -514,7 +514,7 @@ fn rustfix_crate(
             // We'll generate new errors below.
             file.errors_applying_fixes.clear();
         }
-        rustfix_and_fix(&mut fixes, rustc, filename, args)?;
+        rustfix_and_fix(&mut fixes, rustc, filename, args, config)?;
         let mut progress_yet_to_be_made = false;
         for (path, file) in fixes.files.iter_mut() {
             if file.errors_applying_fixes.is_empty() {
@@ -556,6 +556,7 @@ fn rustfix_and_fix(
     rustc: &ProcessBuilder,
     filename: &Path,
     args: &FixArgs,
+    config: &Config,
 ) -> Result<(), Error> {
     // If not empty, filter by these lints.
     // TODO: implement a way to specify this.
@@ -609,6 +610,8 @@ fn rustfix_and_fix(
     // Collect suggestions by file so we can apply them one at a time later.
     let mut file_map = HashMap::new();
     let mut num_suggestion = 0;
+    // It's safe since we won't read any content under home dir.
+    let home_path = config.home().as_path_unlocked();
     for suggestion in suggestions {
         trace!("suggestion");
         // Make sure we've got a file associated with this suggestion and all
@@ -627,6 +630,11 @@ fn rustfix_and_fix(
             continue;
         };
 
+        // Do not write into registry cache. See rust-lang/cargo#9857.
+        if Path::new(&file_name).starts_with(home_path) {
+            continue;
+        }
+
         if !file_names.clone().all(|f| f == &file_name) {
             trace!("rejecting as it changes multiple files: {:?}", suggestion);
             continue;

tests/testsuite/fix.rs

@@ -1791,3 +1791,47 @@ fn non_edition_lint_migration() {
     // Check that it made the edition migration.
     assert!(contents.contains("from_utf8(crate::foo::FOO)"));
 }
+
+// For rust-lang/cargo#9857
+#[cargo_test]
+fn fix_in_dependency() {
+    Package::new("bar", "1.0.0")
+        .file(
+            "src/lib.rs",
+            r#"
+                #[macro_export]
+                macro_rules! m {
+                    ($i:tt) => {
+                        let $i = 1;
+                    };
+                }
+            "#,
+        )
+        .publish();
+
+    let p = project()
+        .file(
+            "Cargo.toml",
+            r#"
+                [package]
+                name = "foo"
+                version = "0.1.0"
+
+                [dependencies]
+                bar = "1.0"
+            "#,
+        )
+        .file(
+            "src/lib.rs",
+            r#"
+                pub fn foo() {
+                    bar::m!(abc);
+                }
+            "#,
+        )
+        .build();
+
+    p.cargo("fix --allow-no-vcs")
+        .with_stderr_does_not_contain("[FIXED] [..]")
+        .run();
+}