feat(toml)!: Update generator by using toml_edit

This is the other main half of toml-rs#340.  Still have deprecations and tests left

Note that strings are rendered differently, see toml-rs#287

By extension this also finishes up toml-rs#396.

BREAKING CHANGES
- `impl Display for toml::Value` now renders as values, not documents, see instead `Table`
- `toml::ser::Serializer` only serializes documents, instead see `toml::ser::ValueSerializer`
- `toml::ser::tables_last` is removed, no longer needed
- `toml::ser::to_vec` is removed to mirror the loss of `from_slice`
- atm `toml::ser::to_string_pretty` just causes larger arrays to be indented
- `toml::ser::Error` is now opaque
- `toml::ser::Serializer::pretty_string` was removed
- `toml::ser::Serializer::pretty_string_literal` was removed
- `toml::ser::Serializer::pretty_array` was removed
- `toml::ser::Serializer::pretty_array_indent` was removed
- `toml::ser::Serializer::pretty_array_trailing_comma` was removed
- `toml::ser::Serializer` is now used used by value, rather than `&mut`

Fixes toml-rs#396

crates/toml/src/fmt.rs

@@ -0,0 +1,68 @@
+#[derive(Copy, Clone)]
+pub(crate) struct DocumentFormatter {
+    pub(crate) multiline_array: bool,
+}
+
+impl Default for DocumentFormatter {
+    fn default() -> Self {
+        Self {
+            multiline_array: false,
+        }
+    }
+}
+
+impl toml_edit::visit_mut::VisitMut for DocumentFormatter {
+    fn visit_document_mut(&mut self, node: &mut toml_edit::Document) {
+        toml_edit::visit_mut::visit_document_mut(self, node);
+    }
+
+    fn visit_item_mut(&mut self, node: &mut toml_edit::Item) {
+        let other = std::mem::take(node);
+        let other = match other.into_table().map(toml_edit::Item::Table) {
+            Ok(i) => i,
+            Err(i) => i,
+        };
+        let other = match other
+            .into_array_of_tables()
+            .map(toml_edit::Item::ArrayOfTables)
+        {
+            Ok(i) => i,
+            Err(i) => i,
+        };
+        *node = other;
+
+        toml_edit::visit_mut::visit_item_mut(self, node);
+    }
+
+    fn visit_table_mut(&mut self, node: &mut toml_edit::Table) {
+        node.decor_mut().clear();
+
+        // Empty tables could be semantically meaningful, so make sure they are not implicit
+        if !node.is_empty() {
+            node.set_implicit(true);
+        }
+
+        toml_edit::visit_mut::visit_table_mut(self, node);
+    }
+
+    fn visit_value_mut(&mut self, node: &mut toml_edit::Value) {
+        node.decor_mut().clear();
+
+        toml_edit::visit_mut::visit_value_mut(self, node);
+    }
+
+    fn visit_array_mut(&mut self, node: &mut toml_edit::Array) {
+        toml_edit::visit_mut::visit_array_mut(self, node);
+
+        if !self.multiline_array || (0..=1).contains(&node.len()) {
+            node.set_trailing("");
+            node.set_trailing_comma(false);
+        } else {
+            for item in node.iter_mut() {
+                item.decor_mut().set_prefix("\n    ");
+            }
+            node.set_trailing("\n");
+            node.set_trailing_comma(true);
+        }
+    }
+}

crates/toml/src/lib.rs

@@ -153,14 +153,16 @@ pub use crate::value::Value;
 
 pub mod ser;
 #[doc(no_inline)]
-pub use crate::ser::{to_string, to_string_pretty, to_vec, Serializer};
+pub use crate::ser::{to_string, to_string_pretty, Serializer};
 pub mod de;
 #[doc(no_inline)]
 pub use crate::de::{from_str, Deserializer, ValueDeserializer};
 
 #[doc(hidden)]
 pub mod macros;
 
+mod fmt;
+
 pub use serde_spanned::Spanned;
 
 // Shortcuts for the module doc-comment