[MRESOURCES-162] Add failOnMissingFilterValue option to fail build on unresolved filter tokens

src/main/java/org/apache/maven/shared/filtering/AbstractMavenFilteringRequest.java

@@ -92,6 +92,15 @@ public class AbstractMavenFilteringRequest {
      */
     private ChangeDetection changeDetection = ChangeDetection.CONTENT;
 
+    /**
+     * When {@code true}, the build fails if a filter expression cannot be resolved (i.e. the
+     * placeholder is left unsubstituted in the output). Defaults to {@code false} to preserve
+     * backward compatibility.
+     *
+     * @since 4.0.0-beta-4
+     */
+    private boolean failOnMissingFilterValue = false;
+
     /**
      * Create instance.
      */
@@ -388,4 +397,26 @@ public ChangeDetection getChangeDetection() {
     public void setChangeDetection(ChangeDetection changeDetection) {
         this.changeDetection = requireNonNull(changeDetection);
     }
+
+    /**
+     * Returns whether the build should fail when a filter expression cannot be resolved.
+     *
+     * @return {@code true} if an unresolved placeholder causes a build failure
+     * @since 4.0.0-beta-4
+     */
+    public boolean isFailOnMissingFilterValue() {
+        return failOnMissingFilterValue;
+    }
+
+    /**
+     * Sets whether the build should fail when a filter expression cannot be resolved.
+     * When {@code true}, any placeholder that has no matching property causes a build failure
+     * instead of being passed through as-is. Defaults to {@code false}.
+     *
+     * @param failOnMissingFilterValue {@code true} to fail on unresolved placeholders
+     * @since 4.0.0-beta-4
+     */
+    public void setFailOnMissingFilterValue(boolean failOnMissingFilterValue) {
+        this.failOnMissingFilterValue = failOnMissingFilterValue;
+    }
 }

src/main/java/org/apache/maven/shared/filtering/BaseFilter.java

@@ -162,7 +162,8 @@ public List<FilterWrapper> getDefaultFilterWrappers(final AbstractMavenFiltering
                 request.getEscapeString(),
                 request.isEscapeWindowsPaths(),
                 request.isSupportMultiLineFiltering(),
-                request.getInterpolatorCustomizer());
+                request.getInterpolatorCustomizer(),
+                request.isFailOnMissingFilterValue());
 
         defaultFilterWrappers.add(wrapper);
 
@@ -216,6 +217,8 @@ private static final class Wrapper extends FilterWrapper {
 
         private final Consumer<Interpolator> interpolatorCustomizer;
 
+        private final boolean failOnMissingFilterValue;
+
         Wrapper(
                 LinkedHashSet<String> delimiters,
                 Project project,
@@ -225,7 +228,8 @@ private static final class Wrapper extends FilterWrapper {
                 String escapeString,
                 boolean escapeWindowsPaths,
                 boolean supportMultiLineFiltering,
-                Consumer<Interpolator> interpolatorCustomizer) {
+                Consumer<Interpolator> interpolatorCustomizer,
+                boolean failOnMissingFilterValue) {
             super();
             this.delimiters = delimiters;
             this.project = project;
@@ -236,6 +240,7 @@ private static final class Wrapper extends FilterWrapper {
             this.escapeWindowsPaths = escapeWindowsPaths;
             this.supportMultiLineFiltering = supportMultiLineFiltering;
             this.interpolatorCustomizer = interpolatorCustomizer;
+            this.failOnMissingFilterValue = failOnMissingFilterValue;
         }
 
         @Override
@@ -268,6 +273,7 @@ public Reader getReader(Reader reader) {
 
             filterReader.setInterpolateWithPrefixPattern(false);
             filterReader.setEscapeString(escapeString);
+            filterReader.setFailOnMissingFilterValue(failOnMissingFilterValue);
 
             return filterReader;
         }

src/main/java/org/apache/maven/shared/filtering/InterpolatorFilterReaderLineEnding.java

@@ -77,6 +77,14 @@ public class InterpolatorFilterReaderLineEnding extends AbstractFilterReaderLine
 
     private boolean eof = false;
 
+    /**
+     * When {@code true}, an unresolved filter expression causes an {@link IOException} instead of
+     * being passed through as-is. Defaults to {@code false}.
+     *
+     * @since 4.0.0-beta-4
+     */
+    private boolean failOnMissingFilterValue = false;
+
     /**
      * @param in reader to use
      * @param interpolator interpolator instance to use
@@ -306,9 +314,15 @@ public int read() throws IOException {
         }
 
         // write away the value if present, otherwise the key unmodified
-        if (value != null) {
+        // Note: the plexus interpolator never returns null — when a token is unresolved it
+        // returns the original expression (i.e. value.equals(key.toString())). We detect
+        // unresolved tokens by comparing value to the original key.
+        boolean resolved = value != null && !value.equals(key.toString());
+        if (resolved) {
             replaceData = value;
             replaceIndex = value.length();
+        } else if (failOnMissingFilterValue) {
+            throw new IOException("Unresolved filter token: '" + key + "'");
         } else {
             replaceData = key.toString();
             replaceIndex = key.length();
@@ -349,4 +363,15 @@ public InterpolatorFilterReaderLineEnding setRecursionInterceptor(RecursionInter
         this.recursionInterceptor = theRecursionInterceptor;
         return this;
     }
+
+    /**
+     * Sets whether the reader should throw an {@link IOException} when a filter expression cannot
+     * be resolved, instead of passing it through as-is. Defaults to {@code false}.
+     *
+     * @param failOnMissingFilterValue {@code true} to fail on unresolved placeholders
+     * @since 4.0.0-beta-4
+     */
+    public void setFailOnMissingFilterValue(boolean failOnMissingFilterValue) {
+        this.failOnMissingFilterValue = failOnMissingFilterValue;
+    }
 }

src/main/java/org/apache/maven/shared/filtering/MavenResourcesExecution.java

@@ -522,6 +522,7 @@ public MavenResourcesExecution copyOf() {
         mre.setDelimiters(new LinkedHashSet<>(this.getDelimiters()));
         mre.setInterpolatorCustomizer(this.getInterpolatorCustomizer());
         mre.setGracefulBinaryHandling(this.isGracefulBinaryHandling());
+        mre.setFailOnMissingFilterValue(this.isFailOnMissingFilterValue());
         return mre;
     }
 

src/main/java/org/apache/maven/shared/filtering/MultiDelimiterInterpolatorFilterReaderLineEnding.java

@@ -83,6 +83,14 @@ public class MultiDelimiterInterpolatorFilterReaderLineEnding extends AbstractFi
 
     private boolean eof = false;
 
+    /**
+     * When {@code true}, an unresolved filter expression causes an {@link IOException} instead of
+     * being passed through as-is. Defaults to {@code false}.
+     *
+     * @since 4.0.0-beta-4
+     */
+    private boolean failOnMissingFilterValue = false;
+
     /**
      * This constructor uses default begin token ${ and default end token }.
      *
@@ -353,9 +361,15 @@ public int read() throws IOException {
         }
 
         // write away the value if present, otherwise the key unmodified
-        if (value != null) {
+        // Note: the plexus interpolator never returns null — when a token is unresolved it
+        // returns the original expression (i.e. value.equals(key.toString())). We detect
+        // unresolved tokens by comparing value to the original key.
+        boolean resolved = value != null && !value.equals(key.toString());
+        if (resolved) {
             replaceData = value;
             replaceIndex = value.length();
+        } else if (failOnMissingFilterValue) {
+            throw new IOException("Unresolved filter token: '" + key + "'");
         } else {
             replaceData = key.toString();
             replaceIndex = key.length();
@@ -399,4 +413,15 @@ public AbstractFilterReaderLineEnding setRecursionInterceptor(RecursionIntercept
         this.recursionInterceptor = givenRecursionInterceptor;
         return this;
     }
+
+    /**
+     * Sets whether the reader should throw an {@link IOException} when a filter expression cannot
+     * be resolved, instead of passing it through as-is. Defaults to {@code false}.
+     *
+     * @param failOnMissingFilterValue {@code true} to fail on unresolved placeholders
+     * @since 4.0.0-beta-4
+     */
+    public void setFailOnMissingFilterValue(boolean failOnMissingFilterValue) {
+        this.failOnMissingFilterValue = failOnMissingFilterValue;
+    }
 }

src/test/java/org/apache/maven/shared/filtering/InterpolatorFilterReaderLineEndingTest.java

@@ -22,15 +22,25 @@
 import java.io.StringReader;
 
 import org.codehaus.plexus.interpolation.Interpolator;
+import org.codehaus.plexus.interpolation.RecursionInterceptor;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.extension.ExtendWith;
+import org.mockito.Mock;
 import org.mockito.junit.jupiter.MockitoExtension;
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertNull;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+import static org.mockito.ArgumentMatchers.eq;
+import static org.mockito.ArgumentMatchers.isA;
+import static org.mockito.Mockito.when;
 
 @ExtendWith(MockitoExtension.class)
 public class InterpolatorFilterReaderLineEndingTest extends AbstractInterpolatorFilterReaderLineEndingTest {
+
+    @Mock
+    private Interpolator mockInterpolator;
+
     @Override
     protected Reader getAaaAaaReader(Reader in, Interpolator interpolator) {
         return new InterpolatorFilterReaderLineEnding(in, interpolator, "aaa", "aaa", true);
@@ -80,4 +90,30 @@ public void setEscapeStringEmptyShouldDisableEscaping() throws Exception {
         reader.setEscapeString("");
         assertNull(reader.getEscapeString());
     }
+
+    @Test
+    public void failOnMissingFilterValueThrowsWhenEnabled() throws Exception {
+        // mockInterpolator returns null → token is unresolved
+        when(mockInterpolator.interpolate(eq("${missing}"), eq(""), isA(RecursionInterceptor.class)))
+                .thenReturn(null);
+
+        InterpolatorFilterReaderLineEnding reader = new InterpolatorFilterReaderLineEnding(
+                new StringReader("value=${missing}"), mockInterpolator, "${", "}", true);
+        reader.setFailOnMissingFilterValue(true);
+
+        assertThrows(java.io.IOException.class, () -> IOUtils.toString(reader));
+    }
+
+    @Test
+    public void failOnMissingFilterValuePassesThroughWhenDisabled() throws Exception {
+        // mockInterpolator returns null → token is unresolved
+        when(mockInterpolator.interpolate(eq("${missing}"), eq(""), isA(RecursionInterceptor.class)))
+                .thenReturn(null);
+
+        InterpolatorFilterReaderLineEnding reader = new InterpolatorFilterReaderLineEnding(
+                new StringReader("value=${missing}"), mockInterpolator, "${", "}", true);
+        reader.setFailOnMissingFilterValue(false);
+
+        assertEquals("value=${missing}", IOUtils.toString(reader));
+    }
 }

src/test/java/org/apache/maven/shared/filtering/MultiDelimiterInterpolatorFilterReaderLineEndingTest.java

@@ -32,6 +32,7 @@
 import org.mockito.junit.jupiter.MockitoExtension;
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertThrows;
 import static org.mockito.ArgumentMatchers.eq;
 import static org.mockito.ArgumentMatchers.isA;
 import static org.mockito.Mockito.when;
@@ -132,4 +133,36 @@ void settingDelimiterSpecsRecalculatesMarkLength() {
 
         assertEquals(markLength, reader.markLength, "mark length should reflect the current delimiter set");
     }
+
+    @Test
+    void failOnMissingFilterValueThrowsWhenEnabled() throws Exception {
+        // interpolator returns null → token is unresolved
+        when(interpolator.interpolate(eq("${missing}"), isA(RecursionInterceptor.class)))
+                .thenReturn(null);
+
+        Reader in = new StringReader("value=${missing}");
+        MultiDelimiterInterpolatorFilterReaderLineEnding reader =
+                new MultiDelimiterInterpolatorFilterReaderLineEnding(in, interpolator, true);
+        reader.setDelimiterSpecs(Collections.singleton("${*}"));
+        reader.setInterpolateWithPrefixPattern(false);
+        reader.setFailOnMissingFilterValue(true);
+
+        assertThrows(java.io.IOException.class, () -> IOUtils.toString(reader));
+    }
+
+    @Test
+    void failOnMissingFilterValuePassesThroughWhenDisabled() throws Exception {
+        // interpolator returns null → token is unresolved
+        when(interpolator.interpolate(eq("${missing}"), isA(RecursionInterceptor.class)))
+                .thenReturn(null);
+
+        Reader in = new StringReader("value=${missing}");
+        MultiDelimiterInterpolatorFilterReaderLineEnding reader =
+                new MultiDelimiterInterpolatorFilterReaderLineEnding(in, interpolator, true);
+        reader.setDelimiterSpecs(Collections.singleton("${*}"));
+        reader.setInterpolateWithPrefixPattern(false);
+        reader.setFailOnMissingFilterValue(false);
+
+        assertEquals("value=${missing}", IOUtils.toString(reader));
+    }
 }