fix: Don't duplicate comments when editing TOML

`toml_edit` <0.22 has a bug that will cause
```toml
[lints]
rust.unsafe_op_in_unsafe_fn = "deny"

rust.explicit_outlives_requirements = "warn"

clippy.cast_lossless = "warn"
clippy.doc_markdown = "warn"
clippy.exhaustive_enums = "warn"
```
to be written out as
[lints]
rust.unsafe_op_in_unsafe_fn = "deny"
rust.explicit_outlives_requirements = "warn"

clippy.cast_lossless = "warn"

clippy.doc_markdown = "warn"

clippy.exhaustive_enums = "warn"
```
when it is parsed and then saved.

See toml-rs/toml#675

This affects any format-preserving edits we do, including:
- `cargo add`
- `cargo remove`
- `cargo init` / `cargo new` editing the workspace

Cargo.toml

@@ -96,8 +96,8 @@ tar = { version = "0.4.40", default-features = false }
 tempfile = "3.9.0"
 thiserror = "1.0.56"
 time = { version = "0.3", features = ["parsing", "formatting", "serde"] }
-toml = "0.8.9"
-toml_edit = { version = "0.21.1", features = ["serde"] }
+toml = "0.8.10"
+toml_edit = { version = "0.22.4", features = ["serde"] }
 tracing = "0.1.40" # be compatible with rustc_log: https://github.com/rust-lang/rust/blob/e51e98dde6a/compiler/rustc_log/Cargo.toml#L9
 tracing-subscriber = { version = "0.3.18", features = ["env-filter"] }
 unicase = "2.7.0"

src/cargo/util/config/mod.rs

@@ -1349,11 +1349,14 @@ impl Config {
                 let doc: toml_edit::Document = arg.parse().with_context(|| {
                     format!("failed to parse value from --config argument `{arg}` as a dotted key expression")
                 })?;
+                fn non_empty(d: Option<&toml_edit::RawString>) -> bool {
+                    d.map_or(false, |p| !p.as_str().unwrap_or_default().trim().is_empty())
+                }
                 fn non_empty_decor(d: &toml_edit::Decor) -> bool {
-                    d.prefix()
-                        .map_or(false, |p| !p.as_str().unwrap_or_default().trim().is_empty())
-                        || d.suffix()
-                            .map_or(false, |s| !s.as_str().unwrap_or_default().trim().is_empty())
+                    non_empty(d.prefix()) || non_empty(d.suffix())
+                }
+                fn non_empty_key_decor(k: &toml_edit::Key) -> bool {
+                    non_empty_decor(k.leaf_decor()) || non_empty_decor(k.dotted_decor())
                 }
                 let ok = {
                     let mut got_to_value = false;
@@ -1367,7 +1370,7 @@ impl Config {
                         let (k, n) = table.iter().next().expect("len() == 1 above");
                         match n {
                             Item::Table(nt) => {
-                                if table.key_decor(k).map_or(false, non_empty_decor)
+                                if table.key(k).map_or(false, non_empty_key_decor)
                                     || non_empty_decor(nt.decor())
                                 {
                                     bail!(
@@ -1384,7 +1387,11 @@ impl Config {
                                 );
                             }
                             Item::Value(v) => {
-                                if non_empty_decor(v.decor()) {
+                                if table
+                                    .key(k)
+                                    .map_or(false, |k| non_empty(k.leaf_decor().prefix()))
+                                    || non_empty_decor(v.decor())
+                                {
                                     bail!(
                                         "--config argument `{arg}` \
                                             includes non-whitespace decoration"