remove trailing whitespace from multi-line tuple struct field prefix

Fixes 5703, Fixes 5525

visibility modifiers always contain a trailing space after them. If the
formatted tuple field needs to be written over multiple lines then the
extra space will cause issues.

In the best case the space will offset the type name by an extra space
and in the worst case it will lead to a "left behind trailing
whitespace" error.

Author: ytmimi

src/items.rs

@@ -1851,7 +1851,7 @@ pub(crate) fn rewrite_struct_field(
     }
 
     let type_annotation_spacing = type_annotation_spacing(context.config);
-    let prefix = rewrite_struct_field_prefix(context, field)?;
+    let mut prefix = rewrite_struct_field_prefix(context, field)?;
 
     let attrs_str = field.attrs.rewrite(context, shape)?;
     let attrs_extendable = field.ident.is_none() && is_attributes_extendable(&attrs_str);
@@ -1894,6 +1894,11 @@ pub(crate) fn rewrite_struct_field(
 
     let is_prefix_empty = prefix.is_empty();
     // We must use multiline. We are going to put attributes and a field on different lines.
+    if context.config.version() == Version::Two {
+        // Remove any additional whitespace at the end of the prefix.
+        // For example if there is a space after a visibility modifier.
+        prefix.truncate(prefix.trim_end().len());
+    }
     let field_str = rewrite_assign_rhs(context, prefix, &*field.ty, &RhsAssignKind::Ty, shape)?;
     // Remove a leading white-space from `rewrite_assign_rhs()` when rewriting a tuple struct.
     let field_str = if is_prefix_empty {

tests/target/issue_5525.rs

@@ -0,0 +1,9 @@
+// rustfmt-version: Two
+
+pub struct SomeCallback(
+    pub extern "C" fn(
+        long_argument_name_to_avoid_wrap: u32,
+        second_long_argument_name: u32,
+        third_long_argument_name: u32,
+    ),
+);

tests/target/issue_5703.rs

@@ -0,0 +1,7 @@
+// rustfmt-version: Two
+
+#[derive(Clone, Debug, Default)]
+pub struct ReactionGroup(
+    pub(in crate::room::timeline)
+        IndexMap<(Option<OwnedTransactionId>, Option<OwnedEventId>), OwnedUserId>,
+);

tests/target/struct_field_doc_comment_v2.rs

@@ -0,0 +1,71 @@
+// rustfmt-version: Two
+
+// #5215
+struct MyTuple(
+    /// Doc Comments
+    /* TODO note to add more to Doc Comments */
+    u32,
+    /// Doc Comments
+    // TODO note
+    u64,
+);
+
+struct MyTuple(
+    #[cfg(unix)] // some comment
+    u64,
+    #[cfg(not(unix))] /*block comment */ u32,
+);
+
+struct MyTuple(
+    #[cfg(unix)]
+    // some comment
+    u64,
+    #[cfg(not(unix))]
+    /*block comment */
+    u32,
+);
+
+struct MyTuple(
+    #[cfg(unix)] // some comment
+    pub u64,
+    #[cfg(not(unix))] /*block comment */ pub(crate) u32,
+);
+
+struct MyTuple(
+    /// Doc Comments
+    /* TODO note to add more to Doc Comments */
+    pub u32,
+    /// Doc Comments
+    // TODO note
+    pub(crate) u64,
+);
+
+struct MyStruct {
+    #[cfg(unix)] // some comment
+    a: u64,
+    #[cfg(not(unix))] /*block comment */ b: u32,
+}
+
+struct MyStruct {
+    #[cfg(unix)] // some comment
+    pub a: u64,
+    #[cfg(not(unix))] /*block comment */ pub(crate) b: u32,
+}
+
+struct MyStruct {
+    /// Doc Comments
+    /* TODO note to add more to Doc Comments */
+    a: u32,
+    /// Doc Comments
+    // TODO note
+    b: u64,
+}
+
+struct MyStruct {
+    /// Doc Comments
+    /* TODO note to add more to Doc Comments */
+    pub a: u32,
+    /// Doc Comments
+    // TODO note
+    pub(crate) b: u64,
+}