From 9c8ad4d85739285905494435bfd4b76455a3f98f Mon Sep 17 00:00:00 2001
From: GustavoSept <136198618+GustavoSept@users.noreply.github.com>
Date: Tue, 12 Nov 2024 18:09:49 -0300
Subject: [PATCH] fix: increase hash size for autogenerated IDs to reduce
 collisions - fixes #978

Co-authored-by: Adrian Hesketh <adrianhesketh@hushmail.com>
---
 .version                                      |  2 +-
 generator/test-css-expression/render_test.go  |  4 ++--
 generator/test-css-middleware/expected.html   |  2 +-
 generator/test-css-middleware/render_test.go  |  2 +-
 generator/test-css-usage/expected.html        | 24 +++++++++----------
 .../test-element-attributes/expected.html     |  8 +++----
 runtime.go                                    |  4 ++--
 runtime_test.go                               | 24 +++++++++++++++++++
 8 files changed, 47 insertions(+), 23 deletions(-)

diff --git a/.version b/.version
index c9ca53fec..8b99f2a59 100644
--- a/.version
+++ b/.version
@@ -1 +1 @@
-0.2.793
\ No newline at end of file
+0.2.796
\ No newline at end of file
diff --git a/generator/test-css-expression/render_test.go b/generator/test-css-expression/render_test.go
index 0214889e1..295b6d8b4 100644
--- a/generator/test-css-expression/render_test.go
+++ b/generator/test-css-expression/render_test.go
@@ -8,8 +8,8 @@ import (
 )
 
 var expected = templ.ComponentCSSClass{
-	ID:    "className_34fc",
-	Class: templ.SafeCSS(`.className_34fc{background-color:#ffffff;max-height:calc(100vh - 170px);color:#ff0000;}`),
+	ID:    "className_34fc0328",
+	Class: templ.SafeCSS(`.className_34fc0328{background-color:#ffffff;max-height:calc(100vh - 170px);color:#ff0000;}`),
 }
 
 func TestCSSExpression(t *testing.T) {
diff --git a/generator/test-css-middleware/expected.html b/generator/test-css-middleware/expected.html
index 622d4d9ac..df6b148e6 100644
--- a/generator/test-css-middleware/expected.html
+++ b/generator/test-css-middleware/expected.html
@@ -1,3 +1,3 @@
-<div class="red_050e">
+<div class="red_050e5e03">
 	Red text
 </div>
diff --git a/generator/test-css-middleware/render_test.go b/generator/test-css-middleware/render_test.go
index cc7f7e4bf..76a86ccb3 100644
--- a/generator/test-css-middleware/render_test.go
+++ b/generator/test-css-middleware/render_test.go
@@ -16,7 +16,7 @@ import (
 //go:embed expected.html
 var expected string
 
-var expectedCSS = `.red_050e{color:red;}
+var expectedCSS = `.red_050e5e03{color:red;}
 `
 
 func Test(t *testing.T) {
diff --git a/generator/test-css-usage/expected.html b/generator/test-css-usage/expected.html
index af4ebf684..ff3319393 100644
--- a/generator/test-css-usage/expected.html
+++ b/generator/test-css-usage/expected.html
@@ -4,33 +4,33 @@
 	}
 	</style>
 <div class="test">Style tags are supported</div>
-<style type="text/css">.cssComponentGreen_58d2{color:#00ff00;}</style>
-<div class="cssComponentGreen_58d2">CSS components are supported</div>
-<div class="cssComponentGreen_58d2 classA &amp;&amp;&amp;classB classC d e" type="button">Both CSS components and constants are supported</div>
-<div class="cssComponentGreen_58d2 classA &amp;&amp;&amp;classB classC d e" type="button">Both CSS components and constants are supported</div>
+<style type="text/css">.cssComponentGreen_58d2872e{color:#00ff00;}</style>
+<div class="cssComponentGreen_58d2872e">CSS components are supported</div>
+<div class="cssComponentGreen_58d2872e classA &amp;&amp;&amp;classB classC d e" type="button">Both CSS components and constants are supported</div>
+<div class="cssComponentGreen_58d2872e classA &amp;&amp;&amp;classB classC d e" type="button">Both CSS components and constants are supported</div>
 <div class="a c">Maps can be used to determine if a class should be added or not.</div>
-<style type="text/css">.e_739d{font-size:14pt;}</style>
-<div class="a c e_739d">KV can be used to conditionally set classes.</div>
+<style type="text/css">.e_739d4573{font-size:14pt;}</style>
+<div class="a c e_739d4573">KV can be used to conditionally set classes.</div>
 <div class="bg-violet-500 hover:bg-red-600 hover:bg-sky-700 text-[#50d71e] w-[calc(100%-4rem)">Psuedo attributes and complex class names are supported.</div>
 <div class="a&#34; onClick=&#34;alert(&#39;hello&#39;)&#34;">
 	Class names are HTML escaped.
 </div>
 <style type="text/css">
- .loading_a3cc{width:50%;}
+ .loading_a3cc3f08{width:50%;}
 </style>
-<div class="loading_a3cc">
+<div class="loading_a3cc3f08">
  CSS components can be used with arguments.
 </div>
 <style type="text/css">
- .loading_9ccc{width:100%;}
+ .loading_9ccc4ca9{width:100%;}
 </style>
-<div class="loading_9ccc">
+<div class="loading_9ccc4ca9">
  CSS components can be used with arguments.
 </div>
 <style type="text/css">
-  .windVaneRotation_b68b{transform:rotate(45deg);}
+  .windVaneRotation_b68b990e{transform:rotate(45deg);}
 </style>
-<div class="windVaneRotation_b68b">
+<div class="windVaneRotation_b68b990e">
   Rotate
 </div>
 
diff --git a/generator/test-element-attributes/expected.html b/generator/test-element-attributes/expected.html
index 5a6f04a48..03680c7d1 100644
--- a/generator/test-element-attributes/expected.html
+++ b/generator/test-element-attributes/expected.html
@@ -1,16 +1,16 @@
 <style type="text/css">
- .important_2ed1{width:100;}
+ .important_2ed176fc{width:100;}
 </style>
 <div style="width: 100;">
  Important
 </div>
 <style type="text/css">
- .unimportant_900a{width:50;}
+ .unimportant_900aeb18{width:50;}
 </style>
-<div style="width: 100;" class="unimportant_900a">
+<div style="width: 100;" class="unimportant_900aeb18">
  Unimportant
 </div>
-<div style="width: 100;" class="unimportant_900a">
+<div style="width: 100;" class="unimportant_900aeb18">
   Else
  </div>
 <div data-script="on click
diff --git a/runtime.go b/runtime.go
index 2009f9f0b..7ed9db99c 100644
--- a/runtime.go
+++ b/runtime.go
@@ -256,11 +256,11 @@ func (css ComponentCSSClass) ClassName() string {
 // CSSID calculates an ID.
 func CSSID(name string, css string) string {
 	sum := sha256.Sum256([]byte(css))
-	hp := hex.EncodeToString(sum[:])[0:4]
+	hs := hex.EncodeToString(sum[:])[0:8] // NOTE: See issue #978. Minimum recommended hs length is 6.
 	// Benchmarking showed this was fastest, and with fewest allocations (1).
 	// Using strings.Builder (2 allocs).
 	// Using fmt.Sprintf (3 allocs).
-	return name + "_" + hp
+	return name + "_" + hs
 }
 
 // NewCSSMiddleware creates HTTP middleware that renders a global stylesheet of ComponentCSSClass
diff --git a/runtime_test.go b/runtime_test.go
index 6f864ea47..4f3d34f18 100644
--- a/runtime_test.go
+++ b/runtime_test.go
@@ -15,6 +15,30 @@ import (
 	"github.com/google/go-cmp/cmp"
 )
 
+func TestCSSID(t *testing.T) {
+	t.Run("minimum hash suffix length is 8", func(t *testing.T) {
+		// See issue #978.
+		name := "classA"
+		css := "background-color:white;"
+		actual := len(templ.CSSID(name, css))
+		expected := len(name) + 1 + 8
+		if expected != actual {
+			t.Errorf("expected length %d, got %d", expected, actual)
+		}
+	})
+	t.Run("known hash collisions are avoided", func(t *testing.T) {
+		name := "classA"
+		// Note that the first 4 characters of the hash are the same.
+		css1 := "grid-column:1;grid-row:1;"  // After hash: f781266f
+		css2 := "grid-column:13;grid-row:6;" // After hash: f781f18b
+		id1 := templ.CSSID(name, css1)
+		id2 := templ.CSSID(name, css2)
+		if id1 == id2 {
+			t.Errorf("hash collision: %s == %s", id1, id2)
+		}
+	})
+}
+
 func TestCSSHandler(t *testing.T) {
 	tests := []struct {
 		name             string