Why Tycho cannot resolve this simple dependency to SWT?

I thought to have studied enough Maven + Tycho to configure at least a minimal target environment for a headless build, but still I am unable to make this small example work. I have three projects:

test, that contains
- sub.ui and
- sub.target

The test project has just a pom.xml that builds the two subprojects and whose only interesting part is the <pluginManagement> section:

...
<build>
 <pluginManagement>
  <plugins>
    <plugin>
      <groupId>org.eclipse.m2e</groupId>
      <artifactId>lifecycle-mapping</artifactId>
      <version>1.0.0</version>
      <configuration>
        <lifecycleMappingMetadata>
          <pluginExecutions>
            <pluginExecution>
              <pluginExecutionFilter>
                <groupId>org.eclipse.tycho</groupId>
                <artifactId>target-platform-configuration</artifactId>
                <versionRange>[1.0.0,)</versionRange>
                <goals>
                  <goal>target-platform</goal>
                </goals>
              </pluginExecutionFilter>
              <action>
                <ignore />
              </action>
            </pluginExecution>
          </pluginExecutions>
        </lifecycleMappingMetadata>
      </configuration>
    </plugin>

    <plugin>
      <groupId>org.eclipse.tycho</groupId>
      <artifactId>tycho-maven-plugin</artifactId>
      <version>${tycho.version}</version>
      <extensions>true</extensions>
    </plugin>

    <plugin>
      <groupId>org.eclipse.tycho</groupId>
      <artifactId>target-platform-configuration</artifactId>
      <version>${tycho.version}</version>
      <configuration>
        <pomDependencies>wrapAsBundle</pomDependencies>
        <target>
          <artifact>
            <groupId>${project.groupId}</groupId>
            <artifactId>sub.target</artifactId>
            <version>0.0.1-SNAPSHOT</version>
          </artifact>
        </target>
        <environments>
          <environment>
            <os>linux</os>
            <ws>gtk</ws>
            <arch>x86</arch>
          </environment>
          <environment>
            <os>linux</os>
            <ws>gtk</ws>
            <arch>x86_64</arch>
          </environment>
          <environment>
            <os>win32</os>
            <ws>win32</ws>
            <arch>x86</arch>
          </environment>
          <environment>
            <os>win32</os>
            <ws>win32</ws>
            <arch>x86_64</arch>
          </environment>
          <environment>
            <os>macosx</os>
            <ws>cocoa</ws>
            <arch>x86_64</arch>
          </environment>
        </environments>
      </configuration>
    </plugin>
  </plugins>
 </pluginManagement>
</build>
...

verbose but quite straightforward (except perhaps for the lifecycle-mapping plugin, that however impacts only when building under Eclipse, and I want to build outside Eclipse). The sub.target project has a canonical pom.xml with just:

...
<build>
 <plugins>
  <plugin>
    <groupId>org.eclipse.tycho</groupId>
    <artifactId>tycho-maven-plugin</artifactId>
  </plugin>

  <plugin>
    <groupId>org.eclipse.tycho</groupId>
    <artifactId>target-platform-configuration</artifactId>
  </plugin>
 </plugins>
</build>
...

and a brief sub.target.target file:

<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<?pde version="3.8"?>
<target includeMode="feature" name="Test" sequenceNumber="1">
  <locations>
    <location includeAllPlatforms="false" includeConfigurePhase="true" includeMode="planner" includeSource="true" type="InstallableUnit">
      <repository location="https://download.eclipse.org/releases/latest/"/>
      <unit id="org.eclipse.equinox.p2.user.ui.feature.group" version="0.0.0"/>
    </location>
  </locations>
  <targetJRE path="org.eclipse.jdt.launching.JRE_CONTAINER/org.eclipse.jdt.internal.debug.ui.launcher.StandardVMType/JavaSE-11"/>
</target>

The sub.ui project is a small plugin project with a silly main that uses a SWT class:

package foo;

import org.eclipse.swt.widgets.Label;

public class Main {
  public static void main(String[] args) {
    Label l = new Label(null, 0);
  }
}

and a MANIFEST.MF:

Manifest-Version: 1.0
Bundle-ManifestVersion: 2
Bundle-Name: Test UI
Bundle-SymbolicName: sub.ui;singleton:=true
Bundle-Version: 0.0.1.qualifier
Automatic-Module-Name: sub.ui
Bundle-RequiredExecutionEnvironment: JavaSE-11
Require-Bundle: org.eclipse.swt

Now, if I open a console and I mvn clear compile, Maven fails while building the Test UI plugin, and displays the errors:

[ERROR] Failed to execute goal org.eclipse.tycho:tycho-compiler-plugin:2.4.0:compile (default-compile) on project sub.ui: Compilation failure: Compilation failure: 
[ERROR] /.../sub.ui/src/foo/Main.java:[3] 
[ERROR]     import org.eclipse.swt.widgets.Label;
[ERROR]            ^^^^^^^^^^^
[ERROR] The import org.eclipse cannot be resolved
[ERROR] /.../sub.ui/src/foo/Main.java:[8] 
[ERROR]     Label l = new Label(null, 0);
[ERROR]     ^^^^^
[ERROR] Label cannot be resolved to a type
[ERROR] /.../sub.ui/src/foo/Main.java:[8] 
[ERROR]     Label l = new Label(null, 0);
[ERROR]                   ^^^^^
[ERROR] Label cannot be resolved to a type
[ERROR] 3 problems (3 errors)

Apparently the build process does not link my code with the SWT version for my macos+cocoa platform, that is nevertheless listed among the plugins in the org.eclipse.equinox.p2.user.ui.feature.group. Strangely, if I launch Maven from Eclipse every now and then it links the right SWT library and completes the build process. What am I missing? How do I convince Tycho to use the information about my platform to consistently select the macos+cocoa SWT jar and link it to my code? I can share the complete example project on GitHub upon request if you cannot spot the mistake in the above code. Thank you for your patience.

Solution

Problem solved. Apparently the x86 platforms are no longer supported (the project I am working on is quite old). If we remove all the x86 <environment>s from the <pluginManagement> section of the main pom.xml file and leave only the x86_64 ones, everything works.