Fix FeatureMacther: featureValueOf may throw

Right now, that may happen in:
- HasToString, if the actual object has a custom toString method which may throw
- FileMatchers.aFileWithCanonicalPath and siblings

Author: alb-i986

hamcrest/src/main/java/org/hamcrest/FeatureMatcher.java

@@ -33,17 +33,23 @@ public FeatureMatcher(Matcher<? super U> subMatcher, String featureDescription,
    * @param actual the target object
    * @return the feature to be matched
    */
-  protected abstract U featureValueOf(T actual);
+  protected abstract U featureValueOf(T actual) throws Exception;
 
   @Override
   protected boolean matchesSafely(T actual, Description mismatch) {
-    final U featureValue = featureValueOf(actual);
-    if (!subMatcher.matches(featureValue)) {
-      mismatch.appendText(featureName).appendText(" ");
-      subMatcher.describeMismatch(featureValue, mismatch);
+    try {
+      final U featureValue = featureValueOf(actual);
+      if (!subMatcher.matches(featureValue)) {
+        mismatch.appendText(featureName).appendText(" ");
+        subMatcher.describeMismatch(featureValue, mismatch);
+        return false;
+      }
+      return true;
+    } catch (Exception e) { // catches exceptions thrown by featureValueOf(), if any
+      mismatch.appendText("an exception was thrown: ");
+      mismatch.appendText(e.toString()); //TODO + stacktrace (?)
       return false;
     }
-    return true;
   }
 
   @Override

hamcrest/src/main/java/org/hamcrest/io/FileMatchers.java

@@ -50,12 +50,8 @@ public static Matcher<File> aFileNamed(final Matcher<String> expected) {
 
     public static Matcher<File> aFileWithCanonicalPath(final Matcher<String> expected) {
         return new FeatureMatcher<File, String>(expected, "A file with canonical path", "path") {
-            @Override protected String featureValueOf(File actual) {
-                try {
-                    return actual.getCanonicalPath();
-                } catch (IOException e) {
-                    return "Exception: " + e.getMessage();
-                }
+            @Override protected String featureValueOf(File actual) throws IOException {
+                return actual.getCanonicalPath();
             }
         };
     }

hamcrest/src/test/java/org/hamcrest/FeatureMatcherTest.java

@@ -33,6 +33,14 @@ public final class FeatureMatcherTest {
         assertEquals("was ShouldNotMatch <ShouldNotMatch>", mismatchDescription.toString());
     }
 
+    @Test public void
+    canRecoverFromFaultyFeature() {
+        assertMismatchDescription(
+                "an exception was thrown: java.lang.UnsupportedOperationException: make the feature fail!",
+                resultMatcher, new FaultyThingy());
+    }
+
+
     public static class Match extends IsEqual<String> {
         public Match(String equalArg) { super(equalArg); }
         @Override public void describeMismatch(Object item, Description description) {
@@ -52,6 +60,17 @@ public String getResult() {
         }
     }
 
+    public static class FaultyThingy extends Thingy {
+        public FaultyThingy() {
+            super("thingy with failing feature");
+        }
+
+        @Override
+        public String getResult() {
+            throw new UnsupportedOperationException("make the feature fail!");
+        }
+    }
+
     public static class ShouldNotMatch {
         @Override public String toString() { return "ShouldNotMatch"; }
     }