fix(autofmt): remove extra whitespace before commas in for-loop tuple patterns (#5384)

* fix(autofmt): remove extra whitespace before commas in for-loop tuple patterns

`dx fmt` was adding spaces before commas in for-loop destructuring
patterns (e.g. `for (index , name , value)`) because `TokenStream::Display`
inserts spaces between every token. Route the pattern through prettyplease
via a new `unparse_pat` helper, following the existing `unparse_expr` pattern.

Fixes #5348

* style: apply rustfmt to writer.rs

---------

Co-authored-by: Jonathan Kelley <jkelleyrtp@gmail.com>

packages/autofmt/src/prettier_please.rs

@@ -7,6 +7,10 @@ impl Writer<'_> {
     pub fn unparse_expr(&mut self, expr: &Expr) -> String {
         unparse_expr(expr, self.raw_src, &self.out.indent)
     }
+
+    pub fn unparse_pat(&self, pat: &syn::Pat) -> String {
+        unparse_pat(pat)
+    }
 }
 
 // we use weird unicode alternatives to avoid conflicts with the actual rsx! macro
@@ -163,6 +167,32 @@ pub fn unparse_inner(expr: &Expr) -> String {
     unwrapped(wrapped)
 }
 
+/// Unparse a pattern into a properly formatted string using prettyplease.
+///
+/// Wraps the pattern in `fn main() { for PAT in () {} }`, formats with prettyplease,
+/// then extracts just the pattern text between "for " and " in".
+pub fn unparse_pat(pat: &syn::Pat) -> String {
+    let file = File {
+        shebang: None,
+        attrs: vec![],
+        items: vec![Item::Verbatim(quote::quote! {
+            fn main() {
+                for #pat in () {}
+            }
+        })],
+    };
+    let formatted = prettyplease::unparse(&file);
+    let after_for = formatted
+        .find("for ")
+        .map(|i| i + 4)
+        .expect("prettyplease output missing 'for' keyword in pattern wrapper");
+    let before_in = formatted[after_for..]
+        .find(" in ")
+        .map(|i| i + after_for)
+        .expect("prettyplease output missing 'in' keyword in pattern wrapper");
+    formatted[after_for..before_in].trim().to_string()
+}
+
 // Split off the fn main and then cut the tabs off the front
 fn unwrapped(raw: String) -> String {
     let mut o = raw

packages/autofmt/src/writer.rs

@@ -153,11 +153,7 @@ impl<'a> Writer<'a> {
     }
 
     fn write_for_loop(&mut self, forloop: &ForLoop) -> std::fmt::Result {
-        write!(
-            self.out,
-            "for {} in ",
-            forloop.pat.clone().into_token_stream(),
-        )?;
+        write!(self.out, "for {} in ", self.unparse_pat(&forloop.pat),)?;
 
         self.write_inline_expr(&forloop.expr)?;
 

packages/autofmt/tests/samples.rs

@@ -64,4 +64,5 @@ twoway![
     expr_on_conditional,
     blank_lines,
     blank_lines_preserved,
+    forloop_tuple,
 ];

packages/autofmt/tests/samples/forloop_tuple.rsx

@@ -0,0 +1,17 @@
+rsx! {
+    for (index, name, value) in data.iter() {
+        div { "{index}: {name} = {value}" }
+    }
+
+    for item in items {
+        div { "{item}" }
+    }
+
+    for (a, b) in pairs.iter().enumerate() {
+        span { "{a}-{b}" }
+    }
+
+    for (_, value) in pairs {
+        span { "{value}" }
+    }
+}