From 819a49413830c47687c0fdce13472f8d3177a1bb Mon Sep 17 00:00:00 2001
From: Cameron Kaiser <classilla@floodgap.com>
Date: Thu, 1 Oct 2020 22:48:46 -0700
Subject: [PATCH] #612: M1224669

---
 layout/generic/nsTextFrame.cpp | 22 ++++++++++++++++------
 1 file changed, 16 insertions(+), 6 deletions(-)

diff --git a/layout/generic/nsTextFrame.cpp b/layout/generic/nsTextFrame.cpp
index 4e345cb45..867d42a9e 100644
--- a/layout/generic/nsTextFrame.cpp
+++ b/layout/generic/nsTextFrame.cpp
@@ -7938,7 +7938,9 @@ nsTextFrame::AddInlineMinISizeForFlow(nsRenderingContext *aRenderingContext,
 
     if (i > wordStart) {
       nscoord width =
-        NSToCoordCeilClamped(textRun->GetAdvanceWidth(wordStart, i - wordStart, &provider));
+        NSToCoordCeilClamped(textRun->GetAdvanceWidth(wordStart, i - wordStart,
+                                                      &provider));
+      width = std::max(0, width);
       aData->currentLine = NSCoordSaturatingAdd(aData->currentLine, width);
       aData->atStartOfLine = false;
 
@@ -7950,8 +7952,11 @@ nsTextFrame::AddInlineMinISizeForFlow(nsRenderingContext *aRenderingContext,
           aData->trailingWhitespace += width;
         } else {
           // Some non-whitespace so the old trailingWhitespace is no longer trailing
-          aData->trailingWhitespace =
-            NSToCoordCeilClamped(textRun->GetAdvanceWidth(trimStart, i - trimStart, &provider));
+          nscoord wsWidth =
+            NSToCoordCeilClamped(textRun->GetAdvanceWidth(trimStart,
+                                                          i - trimStart,
+                                                          &provider));
+          aData->trailingWhitespace = std::max(0, wsWidth);
         }
       } else {
         aData->trailingWhitespace = 0;
@@ -8090,7 +8095,9 @@ nsTextFrame::AddInlinePrefISizeForFlow(nsRenderingContext *aRenderingContext,
 
     if (i > lineStart) {
       nscoord width =
-        NSToCoordCeilClamped(textRun->GetAdvanceWidth(lineStart, i - lineStart, &provider));
+        NSToCoordCeilClamped(textRun->GetAdvanceWidth(lineStart, i - lineStart,
+                                                      &provider));
+      width = std::max(0, width);
       aData->currentLine = NSCoordSaturatingAdd(aData->currentLine, width);
 
       if (collapseWhitespace) {
@@ -8101,8 +8108,11 @@ nsTextFrame::AddInlinePrefISizeForFlow(nsRenderingContext *aRenderingContext,
           aData->trailingWhitespace += width;
         } else {
           // Some non-whitespace so the old trailingWhitespace is no longer trailing
-          aData->trailingWhitespace =
-            NSToCoordCeilClamped(textRun->GetAdvanceWidth(trimStart, i - trimStart, &provider));
+          nscoord wsWidth =
+            NSToCoordCeilClamped(textRun->GetAdvanceWidth(trimStart,
+                                                          i - trimStart,
+                                                          &provider));
+          aData->trailingWhitespace = std::max(0, wsWidth);
         }
       } else {
         aData->trailingWhitespace = 0;