fix(add): Reduce the chance we re-format the user's [features] table

src/cargo/util/toml_mut/manifest.rs

@@ -496,6 +496,11 @@ fn fix_feature_activations(
     for idx in remove_list.iter().rev() {
         feature_values.remove(*idx);
     }
+    if !remove_list.is_empty() {
+        // HACK: Instead of cleaning up the users formatting from having removed a feature, we just
+        // re-format the whole feature list
+        feature_values.fmt();
+    }
 
     if status == DependencyStatus::Required {
         for value in feature_values.iter_mut() {
@@ -511,13 +516,13 @@ fn fix_feature_activations(
             } = parsed_value
             {
                 if dep_name == dep_key && weak {
-                    *value = format!("{dep_name}/{dep_feature}").into();
+                    let mut new_value = toml_edit::Value::from(format!("{dep_name}/{dep_feature}"));
+                    *new_value.decor_mut() = value.decor().clone();
+                    *value = new_value;
                 }
             }
         }
     }
-
-    feature_values.fmt();
 }
 
 pub fn str_or_1_len_table(item: &toml_edit::Item) -> bool {

tests/testsuite/cargo_add/mod.rs

@@ -96,6 +96,7 @@ mod path_dev;
 mod path_inferred_name;
 mod path_inferred_name_conflicts_full_feature;
 mod path_normalized_name;
+mod preserve_features_table;
 mod preserve_sorted;
 mod preserve_unsorted;
 mod quiet;

tests/testsuite/cargo_add/preserve_features_table/in/Cargo.toml

@@ -0,0 +1,21 @@
+[package]
+name = "xxx"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+your-face = { version = "99999.0.0", optional = true }
+
+[features]
+default = [
+  "a",
+  "b",
+  "c",
+]
+a = [
+  "your-face?/nose",  # but not the mouth and nose
+]
+b = []
+c = []

tests/testsuite/cargo_add/preserve_features_table/mod.rs

@@ -0,0 +1,31 @@
+use cargo_test_support::compare::assert_ui;
+use cargo_test_support::prelude::*;
+use cargo_test_support::Project;
+
+use cargo_test_support::curr_dir;
+
+#[cargo_test]
+fn case() {
+    cargo_test_support::registry::init();
+    cargo_test_support::registry::Package::new("your-face", "99999.0.0+my-package")
+        .feature("nose", &[])
+        .feature("mouth", &[])
+        .feature("eyes", &[])
+        .feature("ears", &[])
+        .publish();
+
+    let project = Project::from_template(curr_dir!().join("in"));
+    let project_root = project.root();
+    let cwd = &project_root;
+
+    snapbox::cmd::Command::cargo_ui()
+        .arg("add")
+        .arg_line("your-face --no-optional")
+        .current_dir(cwd)
+        .assert()
+        .success()
+        .stdout_matches_path(curr_dir!().join("stdout.log"))
+        .stderr_matches_path(curr_dir!().join("stderr.log"));
+
+    assert_ui().subset_matches(curr_dir!().join("out"), &project_root);
+}

tests/testsuite/cargo_add/preserve_features_table/out/Cargo.toml

@@ -0,0 +1,21 @@
+[package]
+name = "xxx"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+your-face = { version = "99999.0.0" }
+
+[features]
+default = [
+  "a",
+  "b",
+  "c",
+]
+a = [
+  "your-face/nose",  # but not the mouth and nose
+]
+b = []
+c = []

tests/testsuite/cargo_add/preserve_features_table/stderr.log

@@ -0,0 +1,7 @@
+    Updating `dummy-registry` index
+      Adding your-face v99999.0.0 to dependencies.
+             Features:
+             - ears
+             - eyes
+             - mouth
+             - nose