refactor(rome_formatter): Extract shared separated logic (#4056)

* refactor(rome_formatter): Extract shared separated logic

* Clippy issues

crates/rome_formatter/src/lib.rs

@@ -35,6 +35,7 @@ pub mod prelude;
 #[cfg(debug_assertions)]
 pub mod printed_tokens;
 pub mod printer;
+pub mod separated;
 mod source_map;
 pub mod trivia;
 mod verbatim;

crates/rome_formatter/src/separated.rs

@@ -0,0 +1,229 @@
+use crate::prelude::*;
+use crate::{write, CstFormatContext, GroupId};
+use rome_rowan::{AstNode, AstSeparatedElement, SyntaxResult, SyntaxToken};
+
+pub trait FormatSeparatedElementRule<N>
+where
+    N: AstNode,
+{
+    type Context;
+    type FormatNode<'a>: Format<Self::Context>
+    where
+        N: 'a;
+    type FormatSeparator<'a>: Format<Self::Context>
+    where
+        N: 'a;
+
+    fn format_node<'a>(&self, node: &'a N) -> Self::FormatNode<'a>;
+    fn format_separator<'a>(
+        &self,
+        separator: &'a SyntaxToken<N::Language>,
+    ) -> Self::FormatSeparator<'a>;
+}
+
+/// Formats a single element inside a separated list.
+#[derive(Debug, Clone, Eq, PartialEq)]
+pub struct FormatSeparatedElement<N, R>
+where
+    N: AstNode,
+    R: FormatSeparatedElementRule<N>,
+{
+    element: AstSeparatedElement<N::Language, N>,
+    rule: R,
+    is_last: bool,
+    /// The separator to write if the element has no separator yet.
+    separator: &'static str,
+    options: FormatSeparatedOptions,
+}
+
+impl<N, R> FormatSeparatedElement<N, R>
+where
+    N: AstNode,
+    R: FormatSeparatedElementRule<N>,
+{
+    /// Returns the node belonging to the element.
+    pub fn node(&self) -> SyntaxResult<&N> {
+        self.element.node()
+    }
+}
+
+impl<N, R, C> Format<C> for FormatSeparatedElement<N, R>
+where
+    N: AstNode,
+    N::Language: 'static,
+    R: FormatSeparatedElementRule<N, Context = C>,
+    C: CstFormatContext<Language = N::Language>,
+{
+    fn fmt(&self, f: &mut Formatter<C>) -> FormatResult<()> {
+        let node = self.element.node()?;
+        let separator = self.element.trailing_separator()?;
+
+        let format_node = self.rule.format_node(node);
+
+        if !self.options.nodes_grouped {
+            format_node.fmt(f)?;
+        } else {
+            group(&format_node).fmt(f)?;
+        }
+
+        // Reuse the existing trailing separator or create it if it wasn't in the
+        // input source. Only print the last trailing token if the outer group breaks
+        if let Some(separator) = separator {
+            let format_separator = self.rule.format_separator(separator);
+
+            if self.is_last {
+                match self.options.trailing_separator {
+                    TrailingSeparator::Allowed => {
+                        // Use format_replaced instead of wrapping the result of format_token
+                        // in order to remove only the token itself when the group doesn't break
+                        // but still print its associated trivia unconditionally
+                        format_only_if_breaks(separator, &format_separator)
+                            .with_group_id(self.options.group_id)
+                            .fmt(f)?;
+                    }
+                    TrailingSeparator::Mandatory => {
+                        write!(f, [format_separator])?;
+                    }
+                    TrailingSeparator::Disallowed => {
+                        // A trailing separator was present where it wasn't allowed, opt out of formatting
+                        return Err(FormatError::SyntaxError);
+                    }
+                    TrailingSeparator::Omit => {
+                        write!(f, [format_removed(separator)])?;
+                    }
+                }
+            } else {
+                write!(f, [format_separator])?;
+            }
+        } else if self.is_last {
+            match self.options.trailing_separator {
+                TrailingSeparator::Allowed => {
+                    write!(
+                        f,
+                        [if_group_breaks(&text(self.separator))
+                            .with_group_id(self.options.group_id)]
+                    )?;
+                }
+                TrailingSeparator::Mandatory => {
+                    text(self.separator).fmt(f)?;
+                }
+                TrailingSeparator::Omit | TrailingSeparator::Disallowed => { /* no op */ }
+            }
+        } else {
+            unreachable!(
+                "This is a syntax error, separator must be present between every two elements"
+            );
+        };
+
+        Ok(())
+    }
+}
+
+/// Iterator for formatting separated elements. Prints the separator between each element and
+/// inserts a trailing separator if necessary
+pub struct FormatSeparatedIter<I, Node, Rule>
+where
+    Node: AstNode,
+{
+    next: Option<AstSeparatedElement<Node::Language, Node>>,
+    rule: Rule,
+    inner: I,
+    separator: &'static str,
+    options: FormatSeparatedOptions,
+}
+
+impl<I, Node, Rule> FormatSeparatedIter<I, Node, Rule>
+where
+    Node: AstNode,
+{
+    pub fn new(inner: I, separator: &'static str, rule: Rule) -> Self {
+        Self {
+            inner,
+            rule,
+            separator,
+            next: None,
+            options: FormatSeparatedOptions::default(),
+        }
+    }
+
+    /// Wraps every node inside of a group
+    pub fn nodes_grouped(mut self) -> Self {
+        self.options.nodes_grouped = true;
+        self
+    }
+
+    pub fn with_trailing_separator(mut self, separator: TrailingSeparator) -> Self {
+        self.options.trailing_separator = separator;
+        self
+    }
+
+    #[allow(unused)]
+    pub fn with_group_id(mut self, group_id: Option<GroupId>) -> Self {
+        self.options.group_id = group_id;
+        self
+    }
+}
+
+impl<I, Node, Rule> Iterator for FormatSeparatedIter<I, Node, Rule>
+where
+    Node: AstNode,
+    I: Iterator<Item = AstSeparatedElement<Node::Language, Node>>,
+    Rule: FormatSeparatedElementRule<Node> + Clone,
+{
+    type Item = FormatSeparatedElement<Node, Rule>;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        let element = self.next.take().or_else(|| self.inner.next())?;
+
+        self.next = self.inner.next();
+        let is_last = self.next.is_none();
+
+        Some(FormatSeparatedElement {
+            element,
+            rule: self.rule.clone(),
+            is_last,
+            separator: self.separator,
+            options: self.options,
+        })
+    }
+}
+
+impl<I, Node, Rule> std::iter::FusedIterator for FormatSeparatedIter<I, Node, Rule>
+where
+    Node: AstNode,
+    I: Iterator<Item = AstSeparatedElement<Node::Language, Node>> + std::iter::FusedIterator,
+    Rule: FormatSeparatedElementRule<Node> + Clone,
+{
+}
+
+impl<I, Node, Rule> std::iter::ExactSizeIterator for FormatSeparatedIter<I, Node, Rule>
+where
+    Node: AstNode,
+    I: Iterator<Item = AstSeparatedElement<Node::Language, Node>> + ExactSizeIterator,
+    Rule: FormatSeparatedElementRule<Node> + Clone,
+{
+}
+
+#[derive(Debug, Copy, Clone, Eq, PartialEq, Default)]
+pub enum TrailingSeparator {
+    /// A trailing separator is allowed and preferred
+    #[default]
+    Allowed,
+
+    /// A trailing separator is not allowed
+    Disallowed,
+
+    /// A trailing separator is mandatory for the syntax to be correct
+    Mandatory,
+
+    /// A trailing separator might be present, but the consumer
+    /// decides to remove it
+    Omit,
+}
+
+#[derive(Debug, Default, Copy, Clone, Eq, PartialEq)]
+pub struct FormatSeparatedOptions {
+    trailing_separator: TrailingSeparator,
+    group_id: Option<GroupId>,
+    nodes_grouped: bool,
+}

crates/rome_js_formatter/src/prelude.rs

@@ -6,6 +6,7 @@ pub(crate) use crate::{
     FormattedIterExt, JsFormatContext, JsFormatter,
 };
 pub use rome_formatter::prelude::*;
+pub use rome_formatter::separated::TrailingSeparator;
 pub use rome_rowan::{AstNode as _, AstNodeList as _, AstSeparatedList as _};
 
-pub use crate::separated::{FormatAstSeparatedListExtension, TrailingSeparator};
+pub(crate) use crate::separated::FormatAstSeparatedListExtension;