From ab10c7c326a7f8a2cc23eb275a8f64e5fdacbb20 Mon Sep 17 00:00:00 2001
From: Will McGugan <willmcgugan@gmail.com>
Date: Sun, 28 May 2023 14:56:05 +0100
Subject: [PATCH] fix zero division error (#2674)

* fix zero division error

* push tests
---
 CHANGELOG.md            |  5 +++++
 src/textual/_resolve.py |  6 ++++--
 tests/test_resolve.py   | 25 +++++++++++++++++++++++++
 3 files changed, 34 insertions(+), 2 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 0676b51aa..83ff8f179 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -7,6 +7,11 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 
 ## Unreleased
 
+
+### Fixed
+
+- Fixed zero division error https://github.com/Textualize/textual/issues/2673
+
 ### Added
 
 - `work` decorator accepts `description` parameter to add debug string https://github.com/Textualize/textual/issues/2597
diff --git a/src/textual/_resolve.py b/src/textual/_resolve.py
index 79a1a1e3e..ff8c792f6 100644
--- a/src/textual/_resolve.py
+++ b/src/textual/_resolve.py
@@ -101,6 +101,8 @@ def resolve_fraction_unit(
     if not remaining_space or not widget_styles:
         return Fraction(1)
 
+    initial_space = remaining_space
+
     def resolve_scalar(
         scalar: Scalar | None, fraction_unit: Fraction = Fraction(1)
     ) -> Fraction | None:
@@ -166,8 +168,8 @@ def resolve_fraction_unit(
 
     return (
         Fraction(remaining_space, remaining_fraction)
-        if remaining_space > 0
-        else Fraction(1)
+        if remaining_fraction > 0
+        else initial_space
     )
 
 
diff --git a/tests/test_resolve.py b/tests/test_resolve.py
index 202299747..ef1961edc 100644
--- a/tests/test_resolve.py
+++ b/tests/test_resolve.py
@@ -5,6 +5,7 @@ import pytest
 
 from textual._resolve import resolve, resolve_fraction_unit
 from textual.css.scalar import Scalar
+from textual.css.styles import Styles
 from textual.geometry import Size
 from textual.widget import Widget
 
@@ -125,6 +126,30 @@ def test_resolve_fraction_unit():
     ) == Fraction(2)
 
 
+def test_resolve_fraction_unit_stress_test():
+    """Check for zero division errors."""
+    # https://github.com/Textualize/textual/issues/2673
+    widget = Widget()
+    styles = widget.styles
+    styles.width = "1fr"
+
+    # We're mainly checking for the absence of zero division errors,
+    # which is a reoccurring theme for this code.
+    for remaining_space in range(1, 101, 10):
+        for max_width in range(1, remaining_space):
+            styles.max_width = max_width
+
+            for width in range(1, remaining_space):
+                resolved_unit = resolve_fraction_unit(
+                    [styles, styles, styles],
+                    Size(width, 24),
+                    Size(width, 24),
+                    Fraction(remaining_space),
+                    "width",
+                )
+                assert resolved_unit <= remaining_space
+
+
 def test_resolve_issue_2502():
     """Test https://github.com/Textualize/textual/issues/2502"""