feat(#896): add auto-fix infrastructure with FxUnsortedMetas fix

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

@@ -0,0 +1,24 @@
+/*
+ * SPDX-FileCopyrightText: Copyright (c) 2016-2026 Objectionary.com
+ * SPDX-License-Identifier: MIT
+ */
+package org.eolang.lints;
+
+import com.jcabi.xml.XML;
+import java.io.IOException;
+
+/**
+ * A fix for a lint defect.
+ * @since 0.2.1
+ */
+@FunctionalInterface
+public interface Fix {
+
+    /**
+     * Apply the fix and return the corrected XMIR.
+     * @param xmir The XMIR to fix
+     * @return Fixed XMIR
+     * @throws IOException If something goes wrong
+     */
+    XML apply(XML xmir) throws IOException;
+}

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

@@ -0,0 +1,52 @@
+/*
+ * SPDX-FileCopyrightText: Copyright (c) 2016-2026 Objectionary.com
+ * SPDX-License-Identifier: MIT
+ */
+package org.eolang.lints;
+
+import com.jcabi.xml.ClasspathSources;
+import com.jcabi.xml.XML;
+import com.jcabi.xml.XSL;
+import com.jcabi.xml.XSLDocument;
+import java.io.IOException;
+import org.cactoos.io.ResourceOf;
+import org.cactoos.scalar.Sticky;
+import org.cactoos.scalar.Unchecked;
+import org.cactoos.text.IoCheckedText;
+import org.cactoos.text.TextOf;
+
+/**
+ * Fix for the {@code unsorted-metas} lint.
+ * Sorts {@code meta} elements inside {@code metas} alphabetically
+ * by their {@code head} and {@code tail} content.
+ * @since 0.2.1
+ */
+public final class FxUnsortedMetas implements Fix {
+
+    /**
+     * The XSL stylesheet.
+     */
+    private final Unchecked<XSL> sheet;
+
+    /**
+     * Ctor.
+     */
+    public FxUnsortedMetas() {
+        this.sheet = new Unchecked<>(
+            new Sticky<>(
+                () -> new XSLDocument(
+                    new IoCheckedText(
+                        new TextOf(
+                            new ResourceOf("org/eolang/fixes/metas/unsorted-metas.xsl")
+                        )
+                    ).asString()
+                ).with(new ClasspathSources())
+            )
+        );
+    }
+
+    @Override
+    public XML apply(final XML xmir) throws IOException {
+        return this.sheet.value().transform(xmir);
+    }
+}

src/main/resources/org/eolang/fixes/metas/unsorted-metas.xsl

@@ -0,0 +1,21 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!--
+ * SPDX-FileCopyrightText: Copyright (c) 2016-2026 Objectionary.com
+ * SPDX-License-Identifier: MIT
+-->
+<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" id="unsorted-metas-fix" version="2.0">
+  <xsl:output encoding="UTF-8" method="xml"/>
+  <xsl:template match="@*|node()">
+    <xsl:copy>
+      <xsl:apply-templates select="@*|node()"/>
+    </xsl:copy>
+  </xsl:template>
+  <xsl:template match="metas">
+    <xsl:copy>
+      <xsl:apply-templates select="@*"/>
+      <xsl:apply-templates select="meta">
+        <xsl:sort select="concat(head, ' ', tail)"/>
+      </xsl:apply-templates>
+    </xsl:copy>
+  </xsl:template>
+</xsl:stylesheet>

src/main/resources/org/eolang/lints/metas/unsorted-metas.xsl

@@ -13,8 +13,8 @@
       <xsl:for-each select="/object/metas/meta">
         <xsl:variable name="meta-text" select="concat(head, ' ', tail)"/>
         <xsl:variable name="previous" select="(preceding-sibling::meta)[1]"/>
-        <xsl:variable name="sibling-text" select="concat($previous/head/text(), ' ', $previous/tail/text())"/>
-        <xsl:if test="$meta-text &lt; $sibling-text">
+        <xsl:variable name="previous-text" select="concat($previous/head/text(), ' ', $previous/tail/text())"/>
+        <xsl:if test="$meta-text &lt; $previous-text">
           <xsl:element name="defect">
             <xsl:variable name="line" select="eo:lineno(@line)"/>
             <xsl:attribute name="line">

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

@@ -0,0 +1,63 @@
+/*
+ * SPDX-FileCopyrightText: Copyright (c) 2016-2026 Objectionary.com
+ * SPDX-License-Identifier: MIT
+ */
+package org.eolang.lints;
+
+import fixtures.EoProgram;
+import java.util.Map;
+import java.util.stream.Collectors;
+import org.cactoos.io.InputOf;
+import org.eolang.jucs.ClasspathSource;
+import org.hamcrest.MatcherAssert;
+import org.hamcrest.Matchers;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.yaml.snakeyaml.Yaml;
+
+/**
+ * Tests for {@link FxUnsortedMetas}.
+ * @since 0.2.1
+ * @todo #896:60min Replace partial meta comparison with exact XMIR match.
+ *  Currently the test only compares the ordered sequence of "head tail"
+ *  strings extracted from the metas section. Since we have a clear 'input'
+ *  and 'output' EO program in each YAML pack, we should compare the full
+ *  XMIR structure of the fixed result against the expected XMIR, ignoring
+ *  only volatile attributes such as @line numbers.
+ */
+final class FxUnsortedMetasTest {
+
+    @ParameterizedTest
+    @ClasspathSource(value = "org/eolang/lints/fixes/unsorted-metas/", glob = "**.yaml")
+    void fixesUnsortedMetas(final String yaml) throws Exception {
+        final Map<String, Object> pack = new Yaml().load(yaml);
+        final Object input = pack.get("input");
+        final Object output = pack.get("output");
+        MatcherAssert.assertThat(
+            "Metas after fix must match the expected order",
+            new FxUnsortedMetas().apply(
+                new EoProgram(
+                    String.valueOf(input.hashCode()),
+                    new InputOf(input.toString())
+                ).parse()
+            ).nodes("/object/metas/meta").stream().map(
+                m -> String.format(
+                    "%s %s",
+                    m.xpath("head/text()").get(0),
+                    m.xpath("tail/text()").get(0)
+                )
+            ).collect(Collectors.toList()),
+            Matchers.equalTo(
+                new EoProgram(
+                    String.valueOf(output.hashCode()),
+                    new InputOf(output.toString())
+                ).parse().nodes("/object/metas/meta").stream().map(
+                    m -> String.format(
+                        "%s %s",
+                        m.xpath("head/text()").get(0),
+                        m.xpath("tail/text()").get(0)
+                    )
+                ).collect(Collectors.toList())
+            )
+        );
+    }
+}

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

@@ -109,14 +109,15 @@ void checksLocationsOfYamlPacks() throws IOException {
     @SuppressWarnings("StreamResourceLeak")
     void catchesLostYamls() throws IOException {
         MatcherAssert.assertThat(
-            "All YAML files must be in allowed locations (single or wpa packs)",
+            "All YAML files must be in allowed locations (single, wpa packs, or fixes)",
             Files.walk(Paths.get("src/test/resources/org/eolang/lints"))
                 .filter(Files::isRegularFile)
                 .filter(LtByXslTest.yamls())
                 .map(path -> path.getParent().getParent().toString()).allMatch(
                     path ->
                         path.endsWith("org/eolang/lints/packs/single")
                             || path.endsWith("org/eolang/lints/packs/wpa")
+                            || path.contains("org/eolang/lints/fixes")
                 ),
             Matchers.equalTo(true)
         );

src/test/resources/org/eolang/lints/fixes/unsorted-metas/sorts-version-and-spdx.yaml

@@ -0,0 +1,19 @@
+# SPDX-FileCopyrightText: Copyright (c) 2016-2026 Objectionary.com
+# SPDX-License-Identifier: MIT
+---
+sheets:
+  - /org/eolang/fixes/metas/unsorted-metas.xsl
+input: |
+  +version 0.0.0
+  +spdx SPDX-License-Identifier: MIT
+
+  # No comments.
+  [] > foo
+    42 > @
+output: |
+  +spdx SPDX-License-Identifier: MIT
+  +version 0.0.0
+
+  # No comments.
+  [] > foo
+    42 > @