From 08733a740473d49004f73a011f6824658f891ba4 Mon Sep 17 00:00:00 2001
From: Daniel Puckowski <puckowski.d@gmail.com>
Date: Sun, 22 Mar 2026 10:13:00 -0400
Subject: [PATCH] fix(issue#4316): color calc inside from expression

* Fix color calc() inside from expression parsing issues.
* Add tests for #4316.
---
 packages/less/lib/less/parser/parser.js                   | 4 ++--
 packages/test-data/tests-unit/color-functions/modern.css  | 6 ++++++
 packages/test-data/tests-unit/color-functions/modern.less | 8 ++++++++
 3 files changed, 16 insertions(+), 2 deletions(-)

diff --git a/packages/less/lib/less/parser/parser.js b/packages/less/lib/less/parser/parser.js
index 6a439fb89..23aa54d6b 100644
--- a/packages/less/lib/less/parser/parser.js
+++ b/packages/less/lib/less/parser/parser.js
@@ -2283,10 +2283,10 @@ const Parser = function Parser(context, imports, fileInfo, currentIndex) {
                 parserInput.save();
 
                 // hsl or rgb or lch operand
-                const match = parserInput.$re(/^[lchrgbs]\s+/);
+                const match = parserInput.$re(/^([lchrgbs])(?=\s|[,/*)]|$)/);
                 if (match) {
                     parserInput.forget();
-                    return new tree.Keyword(match[0]);
+                    return new tree.Keyword(match[1]);
                 }
 
                 parserInput.restore();
diff --git a/packages/test-data/tests-unit/color-functions/modern.css b/packages/test-data/tests-unit/color-functions/modern.css
index ed84e9002..bdf2626a4 100644
--- a/packages/test-data/tests-unit/color-functions/modern.css
+++ b/packages/test-data/tests-unit/color-functions/modern.css
@@ -34,3 +34,9 @@
 .color-rgb-div {
   background: rgb(from #0000FF calc(r / 2) g b);
 }
+.color-rgb-sub-right-operand {
+  background: rgb(from blue calc(100 - r) g b);
+}
+.color-rgb-add-left-operand {
+  background: rgb(from blue calc(r + 100) g b);
+}
diff --git a/packages/test-data/tests-unit/color-functions/modern.less b/packages/test-data/tests-unit/color-functions/modern.less
index cf04e2c9b..23445d125 100644
--- a/packages/test-data/tests-unit/color-functions/modern.less
+++ b/packages/test-data/tests-unit/color-functions/modern.less
@@ -46,3 +46,11 @@
 .color-rgb-div {
   background: rgb(from #0000FF calc(r / 2) g b);
 }
+
+.color-rgb-sub-right-operand {
+  background: rgb(from blue calc(100 - r) g b);
+}
+
+.color-rgb-add-left-operand {
+  background: rgb(from blue calc(r + 100) g b);
+}