Bug 1628041 - Use fill length rather than index to indicate a repeat(auto) in subgrid from Servo r=mats

Differential Revision: https://phabricator.services.mozilla.com/D70066

layout/generic/nsGridContainerFrame.cpp

@@ -1410,22 +1410,18 @@ class MOZ_STACK_CLASS nsGridContainerFrame::LineNameMap {
       mClampMaxLine = 1 + aRange->Extent();
       mRepeatAutoEnd = mRepeatAutoStart;
       const auto& styleSubgrid = aTracks.mTemplate.AsSubgrid();
-      const auto fillStart = styleSubgrid->fill_start;
-      // Use decltype so we do not rely on the exact type that was exposed from
-      // rust code.
-      mHasRepeatAuto =
-          fillStart != std::numeric_limits<decltype(fillStart)>::max();
+      const auto fillLen = styleSubgrid->fill_len;
+      mHasRepeatAuto = fillLen != 0;
       if (mHasRepeatAuto) {
         const auto& lineNameLists = styleSubgrid->names;
-        int32_t extraAutoFillLineCount = mClampMaxLine - lineNameLists.Length();
+        const int32_t extraAutoFillLineCount =
+            mClampMaxLine - lineNameLists.Length();
         // Maximum possible number of repeat name lists. This must be reduced
         // to a whole number of repetitions of the fill length.
-        const uint32_t possibleRepeatLength = std::max<int32_t>(
-            0, extraAutoFillLineCount + styleSubgrid->fill_len);
-        MOZ_ASSERT(styleSubgrid->fill_len > 0);
-        const uint32_t repeatRemainder =
-            possibleRepeatLength % styleSubgrid->fill_len;
-        mRepeatAutoStart = fillStart;
+        const uint32_t possibleRepeatLength =
+            std::max<int32_t>(0, extraAutoFillLineCount + fillLen);
+        const uint32_t repeatRemainder = possibleRepeatLength % fillLen;
+        mRepeatAutoStart = styleSubgrid->fill_start;
         mRepeatAutoEnd =
             mRepeatAutoStart + possibleRepeatLength - repeatRemainder;
       }

servo/components/style/values/generics/grid.rs

@@ -714,7 +714,7 @@ impl Parse for LineNameList {
             line_names.truncate(MAX_GRID_LINE as usize);
         }
 
-        let (fill_start, fill_len) = fill_data.unwrap_or((usize::MAX, 0));
+        let (fill_start, fill_len) = fill_data.unwrap_or((0, 0));
 
         Ok(LineNameList {
             names: line_names.into(),
@@ -733,7 +733,7 @@ impl ToCss for LineNameList {
         let fill_start = self.fill_start;
         let fill_len = self.fill_len;
         for (i, names) in self.names.iter().enumerate() {
-            if i == fill_start {
+            if fill_len > 0 && i == fill_start {
                 dest.write_str(" repeat(auto-fill,")?;
             }
 
@@ -748,7 +748,7 @@ impl ToCss for LineNameList {
             }
 
             dest.write_str("]")?;
-            if i == fill_start + fill_len - 1 {
+            if fill_len > 0 && i == fill_start + fill_len - 1 {
                 dest.write_str(")")?;
             }
         }