Disable the dir-name profile setting.

dir-name primarily exists for translating the built-in profiles. In
order to simplify the UI, we would like to not expose it to the user for
the initial stabilization. The code to support it is kept in case we
want to add it in the future.

Author: ehuss

src/cargo/util/toml/mod.rs

@@ -520,16 +520,16 @@ impl TomlProfile {
             features.require(Feature::named_profiles())?;
         }
 
-        if self.dir_name.is_some() {
-            features.require(Feature::named_profiles())?;
-        }
-
-        // `dir-name` validation
-        match &self.dir_name {
-            None => {}
-            Some(dir_name) => {
-                Self::validate_name(dir_name, "dir-name")?;
-            }
+        if let Some(dir_name) = self.dir_name {
+            // This is disabled for now, as we would like to stabilize named
+            // profiles without this, and then decide in the future if it is
+            // needed. This helps simplify the UI a little.
+            bail!(
+                "dir-name=\"{}\" in profile `{}` is not currently allowed, \
+                 directory names are tied to the profile name for custom profiles",
+                dir_name,
+                name
+            );
         }
 
         // `inherits` validation

tests/testsuite/profile_custom.rs

@@ -100,6 +100,7 @@ Caused by:
 }
 
 #[cargo_test]
+#[ignore] // dir-name is currently disabled
 fn invalid_dir_name() {
     let p = project()
         .file(
@@ -134,6 +135,42 @@ Caused by:
         .run();
 }
 
+#[cargo_test]
+fn dir_name_disabled() {
+    let p = project()
+        .file(
+            "Cargo.toml",
+            r#"
+                cargo-features = ["named-profiles"]
+
+                [package]
+                name = "foo"
+                version = "0.1.0"
+
+                [profile.release-lto]
+                inherits = "release"
+                dir-name = "lto"
+                lto = true
+            "#,
+        )
+        .file("src/lib.rs", "")
+        .build();
+
+    p.cargo("build")
+        .masquerade_as_nightly_cargo()
+        .with_status(101)
+        .with_stderr(
+            "\
+error: failed to parse manifest at `[ROOT]/foo/Cargo.toml`
+
+Caused by:
+  dir-name=\"lto\" in profile `release-lto` is not currently allowed, \
+  directory names are tied to the profile name for custom profiles
+",
+        )
+        .run();
+}
+
 #[cargo_test]
 fn invalid_inherits() {
     let p = project()