toml_edit: value is not written if table is constructed beforehand

[tingerrr]

The following code simply discards the last write to the tests sub-key.

use toml_edit::{DocumentMut, value};

fn main() {
    let toml = "";
    let mut doc = toml.parse::<DocumentMut>().expect("invalid doc");
    // doc["tool"] = toml_edit::table();
    // doc["tool"]["typst-test"] = toml_edit::table();
    doc["tool"]["typst-test"]["tests"] = value("tests");
    println!("doc: \n{}\n", doc.to_string());
}

Produces the following output:

tool = { typst-test = { tests = "tests" } }

Uncommenting the second line produces:

tool = {}

Uncommenting the second and first line produces:

[tool]

[tool.typst-test]
tests = "tests"

When inspecting the table tool.typst-test, the value exists, it's simply not written.

[epage]

I've updated the reproduction case to make it easier to follow

#!/usr/bin/env nargo
---
[dependencies]
toml_edit = "0.22"
---

use toml_edit::{DocumentMut, value};

fn main() {
    let toml = "";
    let mut doc = toml.parse::<DocumentMut>().expect("invalid doc");
    doc["tool"]["typst-test"]["tests"] = value("tests");
    println!("doc: \n{}\n", doc.to_string());

    let toml = "";
    let mut doc = toml.parse::<DocumentMut>().expect("invalid doc");
    doc["tool"] = toml_edit::table();
    doc["tool"]["typst-test"]["tests"] = value("tests");
    println!("doc: \n{}\n", doc.to_string());

    let toml = "";
    let mut doc = toml.parse::<DocumentMut>().expect("invalid doc");
    doc["tool"]["typst-test"] = toml_edit::table();
    doc["tool"]["typst-test"]["tests"] = value("tests");
    println!("doc: \n{}\n", doc.to_string());

    let toml = "";
    let mut doc = toml.parse::<DocumentMut>().expect("invalid doc");
    doc["tool"] = toml_edit::table();
    doc["tool"]["typst-test"] = toml_edit::table();
    doc["tool"]["typst-test"]["tests"] = value("tests");
    println!("doc: \n{}\n", doc.to_string());
}

$ ./toml_edit-762.rs
warning: `package.edition` is unspecified, defaulting to `2021`
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.05s
     Running `/home/epage/.cargo/target/84/93c6f0d3e9e9a2/debug/toml_edit-762`
doc:
tool = { typst-test = { tests = "tests" } }


doc:
[tool]
typst-test = { tests = "tests" }


doc:
tool = {}


doc:
[tool]

[tool.typst-test]
tests = "tests"

[epage]

To understand whats going on, I'm going to show the debug repr

[/home/epage/.cargo/target/84/93c6f0d3e9e9a2/toml_edit-762.rs:25:5] &doc = DocumentMut {
    root: Table(
        Table {
            decor: Decor {
                prefix: "default",
                suffix: "default",
            },
            implicit: false,
            dotted: false,
            doc_position: None,
            span: None,
            items: {
                "tool": TableKeyValue {
                    key: Key {
                        key: "tool",
                        repr: None,
                        leaf_decor: Decor {
                            prefix: "default",
                            suffix: "default",
                        },
                        dotted_decor: Decor {
                            prefix: "default",
                            suffix: "default",
                        },
                    },
                    value: Value(
                        InlineTable(
                            InlineTable {
                                preamble: empty,
                                implicit: false,
                                decor: Decor {
                                    prefix: "default",
                                    suffix: "default",
                                },
                                span: None,
                                dotted: false,
                                items: {
                                    "typst-test": TableKeyValue {
                                        key: Key {
                                            key: "typst-test",
                                            repr: None,
                                            leaf_decor: Decor {
                                                prefix: "default",
                                                suffix: "default",
                                            },
                                            dotted_decor: Decor {
                                                prefix: "default",
                                                suffix: "default",
                                            },
                                        },
                                        value: Table(
                                            Table {
                                                decor: Decor {
                                                    prefix: "default",
                                                    suffix: "default",
                                                },
                                                implicit: false,
                                                dotted: false,
                                                doc_position: None,
                                                span: None,
                                                items: {
                                                    "tests": TableKeyValue {
                                                        key: Key {
                                                            key: "tests",
                                                            repr: None,
                                                            leaf_decor: Decor {
                                                                prefix: "default",
                                                                suffix: "default",
                                                            },
                                                            dotted_decor: Decor {
                                                                prefix: "default",
                                                                suffix: "default",
                                                            },
                                                        },
                                                        value: Value(
                                                            String(
                                                                Formatted {
                                                                    value: "tests",
                                                                    repr: "default",
                                                                    decor: Decor {
                                                                        prefix: "default",
                                                                        suffix: "default",
                                                                    },
                                                                },
                                                            ),
                                                        ),
                                                    },
                                                },
                                            },
                                        ),
                                    },
                                },
                            },
                        ),
                    ),
                },
            },
        },
    ),
    trailing: empty,
}

InlineTables are implicitly being created. When we go to render the values in an InlineTable but we come across a Table, we ignore it.

[epage]

Unsure how well this is documented (I wanted to do the above before confirming) but

doc["tool"]["typst-test"]["tests"] = value("tests");

always produces inline tables for the intermediate tables and its left to the caller to put in standard tables, correctly, if they want that.

The question is what we should do moving forward

• Leave it as-is
• Add an assert when inserting, with [], a standard table into a Value
• Change the rendering code to implicitly convert standard tables into inline tables / arrays.

[tingerrr]

always produces inline tables for the intermediate tables and its left to the caller to put in standard tables, correctly, if they want that.

I think that's the part that confused me when I initially used it (it makes somewhat sense in hindsight). An assertion seems like the best option to me, implicit conversion could cause problems elsewhere and be even more confusing, and leaving it as is, just seems wrong. It should definitely not swallow whatever I put in there without warning.

[epage]

Created a test case

#[test]
fn table_under_inline() {
    let mut doc = DocumentMut::new();
    doc["tool"]["typst-test"] = table();
    doc["tool"]["typst-test"]["tests"] = value("tests");

    assert_data_eq!(doc.to_string(), str![[r#"
tool = {}

"#]]);
}

Another approach is we switch from creating inline tables implicitly to we create Tables implicitly unless we are in a Value and then we create an InlineTable. While it doesn't solve all problems, it will make it so there is less of a chance of people using the API incorrectly.