Fix generic default type assignment panic

src/lists.rs

@@ -780,7 +780,7 @@ where
                 pre_comment,
                 pre_comment_style,
                 // leave_last is set to true only for rewrite_items
-                item: if self.inner.peek().is_none() && self.leave_last {
+                item: if is_last && self.leave_last {
                     Err(RewriteError::SkipFormatting)
                 } else {
                     (self.get_item_string)(&item)

src/overflow.rs

@@ -634,7 +634,7 @@ impl<'a> Context<'a> {
             |item| item.rewrite_result(self.context, self.nested_shape),
             span.lo(),
             span.hi(),
-            true,
+            self.items.len() > 1,
         );
         let mut list_items: Vec<_> = items.collect();
 

src/types.rs

@@ -725,13 +725,46 @@ impl Rewrite for ast::GenericParam {
                 TypeDensity::Compressed => "=",
                 TypeDensity::Wide => " = ",
             };
-            param.push_str(eq_str);
-            let budget = shape
+            // Need to allow the space required for the rewrite instead of bailing
+            // regardless of if the line overflows. If it doesn't overflow, it's split.
+            // If it still overflows, then the identifier is too long,
+            // which the user will have to deal with.
+            let rewrite = def.rewrite_result(
+                context,
+                Shape::legacy(usize::MAX, shape.indent + param.len()),
+            )?;
+            let can_fit_in_line = shape
                 .width
-                .checked_sub(param.len())
-                .max_width_error(shape.width, self.span())?;
-            let rewrite =
-                def.rewrite_result(context, Shape::legacy(budget, shape.indent + param.len()))?;
+                .saturating_sub(param.len())
+                .saturating_sub(eq_str.len())
+                .checked_sub(rewrite.len())
+                .is_some();
+            if can_fit_in_line {
+                param.push_str(eq_str);
+            } else {
+                // Begin a new line
+                param.push('\n');
+                for _ in 0..shape.indent.block_indent {
+                    param.push(' ');
+                }
+                let can_fit_in_line_with_eq_str = shape
+                    .width
+                    .saturating_sub(eq_str.len().min(2))
+                    .checked_sub(rewrite.len())
+                    .is_some();
+                if can_fit_in_line_with_eq_str {
+                    // Fits together with eq, remove leading whitespace
+                    param.push_str(eq_str.trim_start());
+                } else {
+                    // Split into three lines, might fit, might not, remove all whitespace,
+                    // eq goes on its own line
+                    param.push_str(eq_str.trim());
+                    param.push('\n');
+                    for _ in 0..shape.indent.block_indent {
+                        param.push(' ');
+                    }
+                }
+            }
             param.push_str(&rewrite);
         }
 

tests/source/issue-6052/repro.rs

@@ -0,0 +1,17 @@
+pub enum ManagementFrameBody<
+    'a,
+    RateIterator = SupportedRatesTLVReadRateIterator<'a>,
+    ExtendedRateIterator = ExtendedSupportedRatesTLVReadRateIterator<'a>,
+    TLVIterator: IntoIterator<Item = IEEE80211TLV<'a, RateIterator, ExtendedRateIterator>> = TLVReadIterator<'a>,
+    ActionFramePayload = &'a [u8],
+>
+{
+    Action(ActionFrameBody<ActionFramePayload>),
+    ActionNoAck(ActionFrameBody<ActionFramePayload>),
+    Beacon(BeaconFrameBody<'a, RateIterator, ExtendedRateIterator, TLVIterator>),
+    ATIM,
+    Unknown {
+        sub_type: ManagementFrameSubtype,
+        body: &'a [u8],
+    },
+}

tests/target/issue-6052/overflows.rs

@@ -0,0 +1,21 @@
+// Passing the max-line boundary seems to be, combined with the other stuff, causing the panic
+pub enum Dummy<
+    SomeVeryLongStructDeclarationAsItemMakingTheLineOverflowTheRightHandSideAssignmentIsImportant
+    = MyDefault,
+> {}
+
+pub enum Dummy2<
+    SomeVeryLongStructDeclarationAsItemMakingTheLineOverflowTheRightHandSideAssignmentIsImport
+    = MyDefault,
+> {}
+
+pub enum Dummy3<
+    SomeVeryLongStructDeclarationAsItemMakingTheLineOverflowTheRightHandSideAssignmentIsImport
+    =
+    MyDefaultThatIsAlsoTooLongToBeFitIntoTheNextLineCausingATripleSplitThisMayBeOverdoingItOrNotIdk,
+> {}
+
+pub enum Dummy4<
+    SomeVeryLongStructDeclarationAsItemMakingTheLineOverflowTheRightHandSideAssignmentIsImport
+    = MyDefaultThatIsAlsoTooLongToBeFitIntoTheNextLineCausingATripleSplitThisMayBeOverdoingItOrNot,
+> {}

tests/target/issue-6052/repro.rs

@@ -0,0 +1,17 @@
+pub enum ManagementFrameBody<
+    'a,
+    RateIterator = SupportedRatesTLVReadRateIterator<'a>,
+    ExtendedRateIterator = ExtendedSupportedRatesTLVReadRateIterator<'a>,
+    TLVIterator: IntoIterator<Item = IEEE80211TLV<'a, RateIterator, ExtendedRateIterator>>
+    = TLVReadIterator<'a>,
+    ActionFramePayload = &'a [u8],
+> {
+    Action(ActionFrameBody<ActionFramePayload>),
+    ActionNoAck(ActionFrameBody<ActionFramePayload>),
+    Beacon(BeaconFrameBody<'a, RateIterator, ExtendedRateIterator, TLVIterator>),
+    ATIM,
+    Unknown {
+        sub_type: ManagementFrameSubtype,
+        body: &'a [u8],
+    },
+}