Remove swt-simple CSS property support (curved tabs removed in SWT)

[vogella]

Summary

• Remove swt-simple CSS property handler registration from plugin.xml — CTabFolder.setSimple() is now deprecated and a no-op in SWT since curved tab support was removed
• Drop swt-simple: false from e4_default_gtk.css (dead configuration)
• Fix pre-existing reflection bug in CTabRendering: field lookup used wrong string "selectionGradientColorsField" instead of "selectionGradientColors"
• Update CTabFolderTest to reflect that getSimple() always returns true
• Update docs/CSS.md to document swt-simple as deprecated

Related

Follows the SWT changes that removed curved tab support from CTabFolder and CTabFolderRenderer.

Test plan

• Run org.eclipse.e4.ui.tests.css.swt — CTabFolderTest#testCTabFolderSimple should pass
• Verify no compilation errors in org.eclipse.e4.ui.workbench.renderers.swt

[eclipse-platform-bot]

This pull request changes some projects for the first time in this development cycle.
Therefore the following files need a version increment:

tests/org.eclipse.e4.ui.tests.css.swt/META-INF/MANIFEST.MF

An additional commit containing all the necessary changes was pushed to the top of this PR's branch. To obtain these changes (for example if you want to push more changes) either fetch from your fork or apply the git patch.

Git patch

From bdd0fa02b94f8207ac40f16109f0b8885b04c2ff Mon Sep 17 00:00:00 2001
From: Eclipse Platform Bot <platform-bot@eclipse.org>
Date: Wed, 1 Apr 2026 15:45:17 +0000
Subject: [PATCH] Version bump(s) for 4.40 stream


diff --git a/tests/org.eclipse.e4.ui.tests.css.swt/META-INF/MANIFEST.MF b/tests/org.eclipse.e4.ui.tests.css.swt/META-INF/MANIFEST.MF
index e6e81a99d5..374046bd91 100644
--- a/tests/org.eclipse.e4.ui.tests.css.swt/META-INF/MANIFEST.MF
+++ b/tests/org.eclipse.e4.ui.tests.css.swt/META-INF/MANIFEST.MF
@@ -2,7 +2,7 @@ Manifest-Version: 1.0
 Bundle-ManifestVersion: 2
 Bundle-Name: %Bundle-Name
 Bundle-SymbolicName: org.eclipse.e4.ui.tests.css.swt; singleton:=true
-Bundle-Version: 0.13.0.qualifier
+Bundle-Version: 0.13.100.qualifier
 Require-Bundle: org.eclipse.e4.ui.css.core,
  org.eclipse.e4.ui.css.swt,
  org.eclipse.e4.ui.css.swt.theme;bundle-version="0.15.0",
-- 
2.53.0

Further information are available in Common Build Issues - Missing version increments.

[github-actions]

Test Results

   852 files  ±0     852 suites  ±0   54m 33s ⏱️ ±0s
 7 890 tests ±0   7 646 ✅ ±0  243 💤 ±0  1 ❌ ±0 
20 172 runs  ±0  19 514 ✅  - 2  655 💤 ±0  3 ❌ +2 

For more details on these failures, see this check.

Results for commit 6b08cd3. ± Comparison against base commit 2928a67.

♻️ This comment has been updated with latest results.