Added linter for warning about unnecessary usage of ^ in code

src/main/java/org/eolang/lints/LtRedundantHat.java

@@ -0,0 +1,60 @@
+/*
+ * SPDX-FileCopyrightText: Copyright (c) 2016-2025 Objectionary.com
+ * SPDX-License-Identifier: MIT
+ */
+package org.eolang.lints;
+
+import com.github.lombrozo.xnav.Xnav;
+import com.jcabi.xml.XML;
+import java.io.IOException;
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.List;
+import java.util.stream.Collectors;
+import org.eolang.parser.OnDefault;
+
+/**
+ * Lint that warns if a redundant {@code ^} is used.
+ *
+ * @since 0.0.60
+ */
+final class LtRedundantHat implements Lint<XML> {
+
+    @Override
+    public Collection<Defect> defects(final XML xmir) throws IOException {
+        final Collection<Defect> defects = new ArrayList<>(0);
+        final Xnav xml = new Xnav(xmir.inner());
+        final List<Xnav> objects = xml.path("//o[@base='^']").collect(Collectors.toList());
+        for (final Xnav object : objects) {
+            final String name = object.attribute("name").text().get();
+            final List<Xnav> parents = object.path(String.format("ancestor::o[.//o[@name='%s']]", name))
+                .collect(Collectors.toList());
+            if (parents.isEmpty()) {
+                defects.add(
+                    new Defect.Default(
+                        this.name(),
+                        Severity.WARNING,
+                        new OnDefault(xmir).get(),
+                        Integer.parseInt(object.attribute("line").text().orElse("0")),
+                        String.format(
+                            "Redundant '^' notation: '%s' can be accessed without it",
+                            name
+                        )
+                    )
+                );
+            }
+        }
+        return defects;
+    }
+
+    @Override
+    public String motive() throws IOException {
+        return "The '^' notation is used when there are no naming conflicts, please omitted for brevity.";
+    }
+
+    @Override
+    public String name() {
+        return "redundant-hat";
+    }
+}
+

src/test/java/org/eolang/lints/LtRedundantHatTest.java

@@ -0,0 +1,55 @@
+/*
+ * SPDX-FileCopyrightText: Copyright (c) 2016-2025 Objectionary.com
+ * SPDX-License-Identifier: MIT
+ */
+package org.eolang.lints;
+
+import com.jcabi.xml.XML;
+import com.jcabi.xml.XMLDocument;
+import java.io.IOException;
+import java.util.Collection;
+import org.hamcrest.MatcherAssert;
+import org.hamcrest.Matchers;
+import org.junit.jupiter.api.Test;
+
+/**
+ * Test case for {@link LtRedundantHat}.
+ *
+ * @since 0.0.60
+ */
+final class LtRedundantHatTest {
+
+    @Test
+    void reportsNoDefectsForNecessaryHat() throws IOException {
+        final XML xml = new XMLDocument(
+                        "<program><object name='foo' line='10'><o name='+test' line='12'></o></object></program>"
+        );
+        final LtRedundantHat lint = new LtRedundantHat();
+        final Collection<Defect> defects = lint.defects(xml);
+        MatcherAssert.assertThat(
+                "Should not report a defect when '^' is necessary to resolve ambiguity",
+                defects,
+                Matchers.empty()
+        );
+    }
+
+    @Test
+    void containsGuidanceInMotive() throws IOException {
+        final LtRedundantHat lint = new LtRedundantHat();
+        MatcherAssert.assertThat(
+                "Motive must explain when to omit redundant '^'",
+                lint.motive(),
+                Matchers.containsString("notation is used when there are no naming conflicts")
+        );
+    }
+
+    @Test
+    void namesStableId() {
+        final LtRedundantHat lint = new LtRedundantHat();
+        MatcherAssert.assertThat(
+                "Rule id must be 'redundant-hat'",
+                lint.name(),
+                Matchers.equalTo("redundant-hat")
+        );
+    }
+}