Don't turn on edition lints for unfixed crates

Currently Cargo runs the risk of turning on the edition lints for crates
which `cargo fix` isn't actually fixing, which means you'll get a huge
deluge of lints that would otherwise be automatically fixable! Fix this
situation by only enabling lints in the same cases that we're actually
applying fixes.

Closes rust-lang-nursery/rustfix#150

src/cargo/ops/fix.rs

@@ -165,7 +165,7 @@ pub fn fix_maybe_exec_rustc() -> CargoResult<bool> {
     // not the best heuristic but matches what Cargo does today at least.
     let mut fixes = FixedCrate::default();
     if let Some(path) = &args.file {
-        if env::var("CARGO_PRIMARY_PACKAGE").is_ok() {
+        if args.primary_package {
             trace!("start rustfixing {:?}", path);
             fixes = rustfix_crate(&lock_addr, rustc.as_ref(), path, &args)?;
         }
@@ -503,6 +503,7 @@ struct FixArgs {
     idioms: bool,
     enabled_edition: Option<String>,
     other: Vec<OsString>,
+    primary_package: bool,
 }
 
 enum PrepareFor {
@@ -543,6 +544,7 @@ impl FixArgs {
             ret.prepare_for_edition = PrepareFor::Next;
         }
         ret.idioms = env::var(IDIOMS_ENV).is_ok();
+        ret.primary_package = env::var("CARGO_PRIMARY_PACKAGE").is_ok();
         ret
     }
 
@@ -554,14 +556,16 @@ impl FixArgs {
             .arg("--cap-lints=warn");
         if let Some(edition) = &self.enabled_edition {
             cmd.arg("--edition").arg(edition);
-            if self.idioms {
+            if self.idioms && self.primary_package {
                 if edition == "2018" { cmd.arg("-Wrust-2018-idioms"); }
             }
         }
+        if self.primary_package {
             if let Some(edition) = self.prepare_for_edition_resolve() {
                 cmd.arg("-W").arg(format!("rust-{}-compatibility", edition));
             }
         }
+    }
 
     /// Verify that we're not both preparing for an enabled edition and enabling
     /// the edition.

tests/testsuite/fix.rs

@@ -1072,3 +1072,47 @@ fn does_not_crash_with_rustc_wrapper() {
         .env("RUSTC_WRAPPER", "/usr/bin/env")
         .run();
 }
+
+#[test]
+fn only_warn_for_relevant_crates() {
+    let p = project()
+        .file(
+            "Cargo.toml",
+            r#"
+                [package]
+                name = "foo"
+                version = "0.1.0"
+
+                [dependencies]
+                a = { path = 'a' }
+            "#,
+        )
+        .file("src/lib.rs", "")
+        .file(
+            "a/Cargo.toml",
+            r#"
+                [package]
+                name = "a"
+                version = "0.1.0"
+            "#,
+        )
+        .file(
+            "a/src/lib.rs",
+            "
+                pub fn foo() {}
+                pub mod bar {
+                    use foo;
+                    pub fn baz() { foo() }
+                }
+            ",
+        )
+        .build();
+
+    p.cargo("fix --allow-no-vcs --edition")
+        .with_stderr("\
+[CHECKING] a v0.1.0 ([..])
+[CHECKING] foo v0.1.0 ([..])
+[FINISHED] dev [unoptimized + debuginfo] target(s) in [..]
+")
+        .run();
+}