ICU-22894 MF2, ICU4J: implements configuring the error handling behavior

icu4j/main/core/src/main/java/com/ibm/icu/message2/DateTimeFormatterFactory.java

@@ -352,7 +352,7 @@ public FormattedPlaceholder format(Object toFormat, Map<String, Object> variable
                             toFormat, new PlainStringFormattedValue("{|" + toFormat + "|}"));
                 }
             } else if (toFormat instanceof Temporal) {
-            	toFormat = JavaTimeConverters.temporalToCalendar((Temporal) toFormat);
+                toFormat = JavaTimeConverters.temporalToCalendar((Temporal) toFormat);
             }
             // Not an else-if here, because the `Temporal` conditions before make `toFormat` a `Calendar`
             if (toFormat instanceof Calendar) {

icu4j/main/core/src/main/java/com/ibm/icu/message2/MFDataModelFormatter.java

@@ -29,6 +29,7 @@
 import com.ibm.icu.message2.MFDataModel.StringPart;
 import com.ibm.icu.message2.MFDataModel.VariableRef;
 import com.ibm.icu.message2.MFDataModel.Variant;
+import com.ibm.icu.message2.MessageFormatter.ErrorHandlingBehavior;
 import com.ibm.icu.util.Calendar;
 import com.ibm.icu.util.CurrencyAmount;
 
@@ -39,15 +40,21 @@
 // TODO: move this in the MessageFormatter?
 class MFDataModelFormatter {
     private final Locale locale;
+    private final ErrorHandlingBehavior errorHandlingBehavior;
     private final MFDataModel.Message dm;
 
     private final MFFunctionRegistry standardFunctions;
     private final MFFunctionRegistry customFunctions;
     private static final MFFunctionRegistry EMPTY_REGISTY = MFFunctionRegistry.builder().build();
 
     MFDataModelFormatter(
-            MFDataModel.Message dm, Locale locale, MFFunctionRegistry customFunctionRegistry) {
+            MFDataModel.Message dm,
+            Locale locale,
+            ErrorHandlingBehavior errorHandlingBehavior,
+            MFFunctionRegistry customFunctionRegistry) {
         this.locale = locale;
+        this.errorHandlingBehavior = errorHandlingBehavior == null
+                ? ErrorHandlingBehavior.BEST_EFFORT : errorHandlingBehavior;
         this.dm = dm;
         this.customFunctions =
                 customFunctionRegistry == null ? EMPTY_REGISTY : customFunctionRegistry;
@@ -94,21 +101,23 @@ String format(Map<String, Object> arguments) {
         if (dm instanceof MFDataModel.PatternMessage) {
             MFDataModel.PatternMessage pm = (MFDataModel.PatternMessage) dm;
             variables = resolveDeclarations(pm.declarations, arguments);
+            if (pm.pattern == null) {
+                fatalFormattingError("The PatternMessage is null.");
+            }
             patternToRender = pm.pattern;
         } else if (dm instanceof MFDataModel.SelectMessage) {
             MFDataModel.SelectMessage sm = (MFDataModel.SelectMessage) dm;
             variables = resolveDeclarations(sm.declarations, arguments);
             patternToRender = findBestMatchingPattern(sm, variables, arguments);
+            if (patternToRender == null) {
+                fatalFormattingError("Cannor find a match for the selector.");
+            }
         } else {
             fatalFormattingError("Unknown message type.");
             // formattingError throws, so the return does not actually happen
             return "ERROR!";
         }
 
-        if (patternToRender == null) {
-            return "ERROR!";
-        }
-
         StringBuilder result = new StringBuilder();
         for (MFDataModel.PatternPart part : patternToRender.parts) {
             if (part instanceof MFDataModel.StringPart) {
@@ -175,15 +184,15 @@ private Pattern findBestMatchingPattern(
                 // spec: Append `rv` as the last element of the list `res`.
                 res.add(rs);
             } else {
-                throw new IllegalArgumentException("Unknown selector type: " + functionName);
+                fatalFormattingError("Unknown selector type: " + functionName);
             }
         }
 
         // This should not be possible, we added one function for each selector,
         // or we have thrown an exception.
         // But just in case someone removes the throw above?
         if (res.size() != selectors.size()) {
-            throw new IllegalArgumentException(
+            fatalFormattingError(
                     "Something went wrong, not enough selector functions, "
                             + res.size() + " vs. " + selectors.size());
         }
@@ -322,8 +331,7 @@ private Pattern findBestMatchingPattern(
         // And should do that only once, when building the data model.
         if (patternToRender == null) {
             // If there was a case with all entries in the keys `*` this should not happen
-            throw new IllegalArgumentException(
-                    "The selection went wrong, cannot select any option.");
+            fatalFormattingError("The selection went wrong, cannot select any option.");
         }
 
         return patternToRender;
@@ -394,7 +402,7 @@ public ResolvedSelector(
         }
     }
 
-    private static void fatalFormattingError(String message) {
+    private static void fatalFormattingError(String message) throws IllegalArgumentException {
         throw new IllegalArgumentException(message);
     }
 
@@ -412,7 +420,7 @@ private FormatterFactory getFormattingFunctionFactoryByName(
                 functionName = customFunctions.getDefaultFormatterNameForType(clazz);
             }
             if (functionName == null) {
-                throw new IllegalArgumentException(
+                fatalFormattingError(
                         "Object to format without a function, and unknown type: "
                                 + toFormat.getClass().getName());
             }
@@ -528,11 +536,17 @@ private FormattedPlaceholder formatExpression(
 
         FormatterFactory funcFactory = getFormattingFunctionFactoryByName(toFormat, functionName);
         if (funcFactory == null) {
+            if (errorHandlingBehavior == ErrorHandlingBehavior.STRICT) {
+                fatalFormattingError("unable to find function at " + fallbackString);
+            }
             return new FormattedPlaceholder(expression, new PlainStringFormattedValue(fallbackString));
         }
         Formatter ff = funcFactory.createFormatter(locale, options);
         String res = ff.formatToString(toFormat, arguments);
         if (res == null) {
+            if (errorHandlingBehavior == ErrorHandlingBehavior.STRICT) {
+                fatalFormattingError("unable to format string at " + fallbackString);
+            }
             res = fallbackString;
         }
 

icu4j/main/core/src/main/java/com/ibm/icu/message2/MessageFormatter.java

@@ -143,13 +143,15 @@
 public class MessageFormatter {
     private final Locale locale;
     private final String pattern;
+    private final ErrorHandlingBehavior errorHandlingBehavior;
     private final MFFunctionRegistry functionRegistry;
     private final MFDataModel.Message dataModel;
     private final MFDataModelFormatter modelFormatter;
 
     private MessageFormatter(Builder builder) {
         this.locale = builder.locale;
         this.functionRegistry = builder.functionRegistry;
+        this.errorHandlingBehavior = builder.errorHandlingBehavior;
         if ((builder.pattern == null && builder.dataModel == null)
                 || (builder.pattern != null && builder.dataModel != null)) {
             throw new IllegalArgumentException(
@@ -171,7 +173,7 @@ private MessageFormatter(Builder builder) {
                         + "Error: " + pe.getMessage() + "\n");
             }
         }
-        modelFormatter = new MFDataModelFormatter(dataModel, locale, functionRegistry);
+        modelFormatter = new MFDataModelFormatter(dataModel, locale, errorHandlingBehavior, functionRegistry);
     }
 
     /**
@@ -201,6 +203,20 @@ public Locale getLocale() {
         return locale;
     }
 
+    /**
+     * Get the {@link ErrorHandlingBehavior} to use when encountering errors in
+     * the current {@code MessageFormatter}.
+     *
+     * @return the error handling behavior.
+     *
+     * @internal ICU 76 technology preview
+     * @deprecated This API is for technology preview only.
+     */
+    @Deprecated
+    public ErrorHandlingBehavior getErrorHandlingBehavior() {
+        return errorHandlingBehavior;
+    }
+
     /**
      * Get the pattern (the serialized message in MessageFormat 2 syntax) of
      * the current {@code MessageFormatter}.
@@ -271,6 +287,37 @@ public FormattedMessage format(Map<String, Object> arguments) {
         throw new RuntimeException("Not yet implemented.");
     }
 
+    /**
+     * Determines how the formatting errors will be handled at runtime.
+     *
+     * <p>Parsing errors and data model errors always throw and will not be affected by this setting.<br>
+     * But resolution errors and formatting errors will either try to fallback (if possible) or throw,
+     * depending on this setting.</p>
+     *
+     * <p>Used in conjunction with the
+     * {@link MessageFormatter.Builder#setErrorHandlingBehavior(ErrorHandlingBehavior)} method.</p>
+     *
+     * @internal ICU 76 technology preview
+     * @deprecated This API is for technology preview only.
+     */
+    @Deprecated
+    public static enum ErrorHandlingBehavior {
+        /**
+         * Suppress errors and return best-effort output.
+         *
+         * @internal ICU 76 technology preview
+         * @deprecated This API is for technology preview only.
+         */
+        BEST_EFFORT,
+        /**
+         * Signal all {@code MessageFormat} errors by throwing a {@link RuntimeException}.
+         *
+         * @internal ICU 76 technology preview
+         * @deprecated This API is for technology preview only.
+         */
+        STRICT
+    }
+
     /**
      * A {@code Builder} used to build instances of {@link MessageFormatter}.
      *
@@ -281,6 +328,7 @@ public FormattedMessage format(Map<String, Object> arguments) {
     public static class Builder {
         private Locale locale = Locale.getDefault(Locale.Category.FORMAT);
         private String pattern = null;
+        private ErrorHandlingBehavior errorHandlingBehavior = ErrorHandlingBehavior.BEST_EFFORT;
         private MFFunctionRegistry functionRegistry = MFFunctionRegistry.builder().build();
         private MFDataModel.Message dataModel = null;
 
@@ -319,6 +367,23 @@ public Builder setPattern(String pattern) {
             return this;
         }
 
+        /**
+         * Sets the {@link ErrorHandlingBehavior} to use when encountering errors at formatting time.
+         *
+         * <p>The default value is {@code ErrorHandlingBehavior.BEST_EFFORT}, trying to fallback.</p>
+         *
+         * @param the error handling behavior to use.
+         * @return the builder, for fluent use.
+         *
+         * @internal ICU 76 technology preview
+         * @deprecated This API is for technology preview only.
+         */
+        @Deprecated
+        public Builder setErrorHandlingBehavior(ErrorHandlingBehavior errorHandlingBehavior) {
+            this.errorHandlingBehavior = errorHandlingBehavior;
+            return this;
+        }
+
         /**
          * Sets an instance of {@link MFFunctionRegistry} that should register any
          * custom functions used by the message.

icu4j/main/core/src/test/java/com/ibm/icu/dev/test/message2/MessageFormat2Test.java

@@ -574,4 +574,85 @@ public void testVariableOptionsInSelectorWithLocalVar() {
         assertEquals("test local vars loop", "Count = 23, OffCount = 21, and delta=2.",
                 mfVar2.formatToString(Args.of("count", 23, "delta", 2)));
     }
+
+    // Needs more tests. Ported from the equivalent test in ICU4C
+    @Test
+    public void testFormatterAPI() {
+        String result;
+        Map<String, Object> messageArguments = new HashMap<>();
+
+        // Check that constructing the formatter fails
+        // if there's a syntax error
+        String pattern = "{{}";
+        MessageFormatter.Builder mfBuilder = MessageFormatter.builder();
+        MessageFormatter mf;
+        try {
+            mf = mfBuilder
+                    // This shouldn't matter, since there's a syntax error
+                    .setErrorHandlingBehavior(MessageFormatter.ErrorHandlingBehavior.BEST_EFFORT)
+                    .setPattern(pattern)
+                    .build();
+            errln("error expected");
+        } catch (IllegalArgumentException e) {
+            assertTrue("", e.getMessage().contains("Parse error"));
+        }
+
+        /*
+          Parsing is done when setPattern() is called,
+          so setErrorHandlingBehavior(MessageFormatter.ErrorHandlingBehavior.STRICT) or setSuppressErrors must be called
+          _before_ setPattern() to get the right behavior,
+          and if either method is called after setting a pattern,
+          setPattern() has to be called again.
+         */
+
+        // Should get the same behavior with strict errors
+        try {
+            mf = mfBuilder.setErrorHandlingBehavior(MessageFormatter.ErrorHandlingBehavior.STRICT)
+                    // Force re-parsing, as above comment
+                    .setPattern(pattern)
+                    .build();
+            errln("error expected");
+        } catch (IllegalArgumentException e) {
+            assertTrue("", e.getMessage().contains("Parse error"));
+        }
+
+        // Try the same thing for a pattern with a resolution error
+        pattern = "{{{$x}}}";
+        // Check that a pattern with a resolution error gives fallback output
+        mf = mfBuilder
+                .setErrorHandlingBehavior(MessageFormatter.ErrorHandlingBehavior.BEST_EFFORT)
+                .setPattern(pattern)
+                .build();
+        result = mf.formatToString(messageArguments);
+        assertEquals("", "{$x}", result);
+
+        try {
+            // Check that we do get an error with strict errors
+            mf = mfBuilder
+                    .setErrorHandlingBehavior(MessageFormatter.ErrorHandlingBehavior.STRICT)
+                    .build();
+            // U_ASSERT(U_SUCCESS(errorCode));
+            result = mf.formatToString(messageArguments);
+            errln("error expected");
+        } catch (IllegalArgumentException e) {
+            assertTrue("", e.getMessage().contains("unable to find function"));
+        }
+
+        // Finally, check a valid pattern
+        pattern = "hello";
+        mf = mfBuilder
+                .setPattern(pattern)
+                .setErrorHandlingBehavior(MessageFormatter.ErrorHandlingBehavior.BEST_EFFORT)
+                .build();
+        result = mf.formatToString(messageArguments);
+        assertEquals("", "hello", result);
+
+        // Check that behavior is the same with strict errors
+        mf = mfBuilder
+                .setErrorHandlingBehavior(MessageFormatter.ErrorHandlingBehavior.STRICT)
+                .build();
+        result = mf.formatToString(messageArguments);
+        assertEquals("", "hello", result);
+    }
+
 }

icu4j/main/core/src/test/java/com/ibm/icu/dev/test/message2/TestUtils.java

@@ -85,8 +85,9 @@ static void rewriteDates(Param[] params) {
         //    "params": [{"name": "exp"}, { "value": { "date": 1722746637000 } }]
         for (int i = 0; i < params.length; i++) {
             Param pair = params[i];
-            if (pair.value instanceof Map) {
-                Map innerMap = (Map) pair.value;
+            if (pair.value instanceof Map<?, ?>) {
+                @SuppressWarnings("unchecked")
+                Map<String, Object> innerMap = (Map<String, Object>) pair.value;
                 if (innerMap.size() == 1 && innerMap.containsKey("date") && innerMap.get("date") instanceof Double) {
                     Long dateValue = Double.valueOf((Double) innerMap.get("date")).longValue();
                     params[i] = new Param(pair.name, new Date(dateValue));
@@ -103,8 +104,9 @@ static void rewriteDecimals(Param[] params) {
         //    "params": [{"name": "val"}, {"value": {"decimal": "1234567890123456789.987654321"}}]
         for (int i = 0; i < params.length; i++) {
             Param pair = params[i];
-            if (pair.value instanceof Map) {
-                Map innerMap = (Map) pair.value;
+            if (pair.value instanceof Map<?, ?>) {
+                @SuppressWarnings("unchecked")
+                Map<String, Object> innerMap = (Map<String, Object>) pair.value;
                 if (innerMap.size() == 1 && innerMap.containsKey("decimal")
                     && innerMap.get("decimal") instanceof String) {
                     String decimalValue = (String) innerMap.get("decimal");