Comments between lines in a table are duplicated

[kpreid]

Repro that just round-trips some toml:

[dependencies]
pretty_assertions = "=1.3.0"
toml_edit = "=0.21.1"

#[test]
fn toml_edit_bug() {
    use pretty_assertions::assert_eq;

    let text = r###"
[workspace.lints]
rust.unsafe_op_in_unsafe_fn = "deny"

rust.explicit_outlives_requirements = "warn"
# rust.unused_crate_dependencies = "warn"

clippy.cast_lossless = "warn"
clippy.doc_markdown = "warn"
clippy.exhaustive_enums = "warn"
"###;

    let manifest: toml_edit::Document = text.parse().unwrap();

    assert_eq!(text, manifest.to_string());
}

The text should be identical, but it is not. Specifically, the whitespace between the first two items is deleted, and the comment and whitespace are duplicated between all following pairs of items.

 [workspace.lints]
 rust.unsafe_op_in_unsafe_fn = "deny"
-
 rust.explicit_outlives_requirements = "warn"
 # rust.unused_crate_dependencies = "warn"
 
 clippy.cast_lossless = "warn"
+# rust.unused_crate_dependencies = "warn"
+
 clippy.doc_markdown = "warn"
+# rust.unused_crate_dependencies = "warn"
+
 clippy.exhaustive_enums = "warn"

The same behavior happens with toml_edit 0.19.15, so this is not a new bug.

[epage]

The core of this problem is that we don't track these dotted keys independently but treat them as one table. Another manifestation of this is #163.

Looking at a dump of the document, the comment is part of the "prefix" of the clippy table, so every time that table shows up, we show the "prefix".

let manifest = Document {
    root: Table(
        Table {
            decor: Decor {
                prefix: "default",
                suffix: "default",
            },
            implicit: false,
            dotted: false,
            doc_position: None,
            span: None,
            items: {
                "rust": TableKeyValue {
                    key: Key {
                        key: "rust",
                        repr: Some(
                            "rust",
                        ),
                        decor: Decor {
                            prefix: "\n",
                            suffix: empty,
                        },
                    },
                    value: Table(
                        Table {
                            decor: Decor {
                                prefix: "default",
                                suffix: "default",
                            },
                            implicit: true,
                            dotted: true,
                            doc_position: None,
                            span: None,
                            items: {
                                "unsafe_op_in_unsafe_fn": TableKeyValue {
                                    key: Key {
                                        key: "unsafe_op_in_unsafe_fn",
                                        repr: Some(
                                            "unsafe_op_in_unsafe_fn",
                                        ),
                                        decor: Decor {
                                            prefix: empty,
                                            suffix: " ",
                                        },
                                    },
                                    value: Value(
                                        String(
                                            Formatted {
                                                value: "deny",
                                                repr: "\"deny\"",
                                                decor: Decor {
                                                    prefix: " ",
                                                    suffix: empty,
                                                },
                                            },
                                        ),
                                    ),
                                },
                                "explicit_outlives_requirements": TableKeyValue {
                                    key: Key {
                                        key: "explicit_outlives_requirements",
                                        repr: Some(
                                            "explicit_outlives_requirements",
                                        ),
                                        decor: Decor {
                                            prefix: empty,
                                            suffix: " ",
                                        },
                                    },
                                    value: Value(
                                        String(
                                            Formatted {
                                                value: "warn",
                                                repr: "\"warn\"",
                                                decor: Decor {
                                                    prefix: " ",
                                                    suffix: empty,
                                                },
                                            },
                                        ),
                                    ),
                                },
                            },
                        },
                    ),
                },
                "clippy": TableKeyValue {
                    key: Key {
                        key: "clippy",
                        repr: Some(
                            "clippy",
                        ),
                        decor: Decor {
                            prefix: "# rust.unused_crate_dependencies = \"warn\"\n\n",
                            suffix: empty,
                        },
                    },
                    value: Table(
                        Table {
                            decor: Decor {
                                prefix: "default",
                                suffix: "default",
                            },
                            implicit: true,
                            dotted: true,
                            doc_position: None,
                            span: None,
                            items: {
                                "cast_lossless": TableKeyValue {
                                    key: Key {
                                        key: "cast_lossless",
                                        repr: Some(
                                            "cast_lossless",
                                        ),
                                        decor: Decor {
                                            prefix: empty,
                                            suffix: " ",
                                        },
                                    },
                                    value: Value(
                                        String(
                                            Formatted {
                                                value: "warn",
                                                repr: "\"warn\"",
                                                decor: Decor {
                                                    prefix: " ",
                                                    suffix: empty,
                                                },
                                            },
                                        ),
                                    ),
                                },
                                "doc_markdown": TableKeyValue {
                                    key: Key {
                                        key: "doc_markdown",
                                        repr: Some(
                                            "doc_markdown",
                                        ),
                                        decor: Decor {
                                            prefix: empty,
                                            suffix: " ",
                                        },
                                    },
                                    value: Value(
                                        String(
                                            Formatted {
                                                value: "warn",
                                                repr: "\"warn\"",
                                                decor: Decor {
                                                    prefix: " ",
                                                    suffix: empty,
                                                },
                                            },
                                        ),
                                    ),
                                },
                                "exhaustive_enums": TableKeyValue {
                                    key: Key {
                                        key: "exhaustive_enums",
                                        repr: Some(
                                            "exhaustive_enums",
                                        ),
                                        decor: Decor {
                                            prefix: empty,
                                            suffix: " ",
                                        },
                                    },
                                    value: Value(
                                        String(
                                            Formatted {
                                                value: "warn",
                                                repr: "\"warn\"",
                                                decor: Decor {
                                                    prefix: " ",
                                                    suffix: empty,
                                                },
                                            },
                                        ),
                                    ),
                                },
                            },
                        },
                    ),
                },
            },
        },
    ),
    trailing: empty,
    original: Some(
        "\nrust.unsafe_op_in_unsafe_fn = \"deny\"\n\nrust.explicit_outlives_requirements = \"warn\"\n# rust.unused_crate_dependencies = \"warn\"\n\nclippy.cast_lossless = \"warn\"\nclippy.doc_markdown = \"warn\"\nclippy.exhaustive_enums = \"warn\"\n",
    ),
    span: None,
}

[epage]

Opened rust-lang/cargo#13402 to make sure cargo gets the fixed behavior

[kpreid]

we don't track these dotted keys independently

Aha, and now I understand why the bug wasn't already noticed — dotted keys are less common.

[epage]

Hadn't considered using dotted keys for lints but I like it!