Make BuildContext.getValue generic

src/main/java/org/codehaus/plexus/build/BuildContext.java

@@ -167,10 +167,16 @@ public interface BuildContext {
      *
      * @see #setValue(String, Object)
      * @see #isIncremental()
+     * <p>
+     * The return type is inferred from the assignment target and is not checked here: a value of another type
+     * than the one the caller expects fails with a {@link ClassCastException} at the call site.
+     * </p>
+     *
+     * @param <T> the expected type of the value
      * @param key a {@link java.lang.String} object.
-     * @return a {@link java.lang.Object} object.
+     * @return the value, or {@code null} if there is none
      */
-    Object getValue(String key);
+    <T> T getValue(String key);
 
     /**
      * <p>addWarning.</p>

src/main/java/org/codehaus/plexus/build/DefaultBuildContext.java

@@ -152,11 +152,12 @@
     }
 
     /** {@inheritDoc} */
-    public Object getValue(String key) {
+    @SuppressWarnings("unchecked")
+    public <T> T getValue(String key) {
         if (isDefaultImplementation()) {
-            return contextMap.get(key);
+            return (T) contextMap.get(key);
         }
-        return legacy.getValue(key);
+        return (T) legacy.getValue(key);
     }
 
     /** {@inheritDoc} */
@@ -168,12 +169,12 @@
     }
 
     /** {@inheritDoc} */
     public void addError(File file, int line, int column, String message, Throwable cause) {
         addMessage(file, line, column, message, SEVERITY_ERROR, cause);
     }
 
     /** {@inheritDoc} */
     public void addWarning(File file, int line, int column, String message, Throwable cause) {
         addMessage(file, line, column, message, SEVERITY_WARNING, cause);
     }
 
@@ -182,7 +183,7 @@
     }
 
     /** {@inheritDoc} */
     public void addMessage(File file, int line, int column, String message, int severity, Throwable cause) {
         if (isDefaultImplementation()) {
             switch (severity) {
                 case BuildContext.SEVERITY_ERROR:
@@ -200,7 +201,7 @@
     }
 
     /** {@inheritDoc} */
     public void removeMessages(File file) {
         if (isDefaultImplementation()) {
             return;
         }

src/test/java/org/codehaus/plexus/build/BuildContextGetValueTypingTest.java

@@ -0,0 +1,29 @@
+package org.codehaus.plexus.build;
+
+/**
+ * Compile-time check that {@link BuildContext#getValue(String)} infers its result type from the assignment target, and
+ * that an implementation declaring the pre-generic {@code Object getValue(String)} still compiles. The module skips
+ * test execution, so this fails the build by not compiling.
+ */
+final class BuildContextGetValueTypingTest {
+
+    private BuildContextGetValueTypingTest() {}
+
+    static String inferredFromAssignment(BuildContext context) {
+        String value = context.getValue("key");
+        return value;
+    }
+
+    static Object plainObjectStillWorks(BuildContext context) {
+        Object value = context.getValue("key");
+        return value;
+    }
+
+    @SuppressWarnings({"unchecked", "rawtypes"})
+    abstract static class PreGenericImplementation implements BuildContext {
+        @Override
+        public Object getValue(String key) {
+            return null;
+        }
+    }
+}