ICU-22902 Remove support for Unsupported, Private & Reserved constructs

Matching PR unicode-org#883 in the message-format-wg repo.

Also move spec tests for unsupported statements and expressions into new files
to serve as syntax error tests.

Author: catamorphism

icu4c/source/common/unicode/utypes.h

@@ -597,15 +597,13 @@ typedef enum UErrorCode {
     U_MF_MISSING_SELECTOR_ANNOTATION_ERROR,  /**< A selector expression evaluates to an unannotated operand. @internal ICU 75 technology preview @deprecated This API is for technology preview only. */
     U_MF_DUPLICATE_DECLARATION_ERROR, /**< The same variable is declared in more than one .local or .input declaration. @internal ICU 75 technology preview @deprecated This API is for technology preview only. */
     U_MF_OPERAND_MISMATCH_ERROR,     /**< An operand provided to a function does not have the required form for that function @internal ICU 75 technology preview @deprecated This API is for technology preview only. */
-    U_MF_UNSUPPORTED_STATEMENT_ERROR, /**< A message includes a reserved statement. @internal ICU 75 technology preview @deprecated This API is for technology preview only. */
-    U_MF_UNSUPPORTED_EXPRESSION_ERROR, /**< A message includes syntax reserved for future standardization or private implementation use. @internal ICU 75 technology preview @deprecated This API is for technology preview only. */
     U_MF_DUPLICATE_VARIANT_ERROR, /**< A message includes a variant with the same key list as another variant. @internal ICU 76 technology preview @deprecated This API is for technology preview only. */
 #ifndef U_HIDE_DEPRECATED_API
     /**
      * One more than the highest normal formatting API error code.
      * @deprecated ICU 58 The numeric value may change over time, see ICU ticket #12420.
      */
-    U_FMT_PARSE_ERROR_LIMIT = 0x10122,
+    U_FMT_PARSE_ERROR_LIMIT = 0x10120,
 #endif  // U_HIDE_DEPRECATED_API
 
     /*

icu4c/source/common/utypes.cpp

@@ -140,8 +140,6 @@ _uFmtErrorName[U_FMT_PARSE_ERROR_LIMIT - U_FMT_PARSE_ERROR_START] = {
     "U_MF_MISSING_SELECTOR_ANNOTATION_ERROR",
     "U_MF_DUPLICATE_DECLARATION_ERROR",
     "U_MF_OPERAND_MISMATCH_ERROR",
-    "U_MF_UNSUPPORTED_STATEMENT_ERROR",
-    "U_MF_UNSUPPORTED_EXPRESSION_ERROR",
     "U_MF_DUPLICATE_VARIANT_ERROR"
 };
 

icu4c/source/i18n/messageformat2.cpp

@@ -241,24 +241,6 @@ FunctionOptions MessageFormatter::resolveOptions(const Environment& env, const O
     return FormattedPlaceholder(fallback);
 }
 
-// Per https://github.com/unicode-org/message-format-wg/blob/main/spec/formatting.md#fallback-resolution
-static UnicodeString reservedFallback (const Expression& e) {
-    UErrorCode localErrorCode = U_ZERO_ERROR;
-    const Operator* rator = e.getOperator(localErrorCode);
-    U_ASSERT(U_SUCCESS(localErrorCode));
-    const Reserved& r = rator->asReserved();
-
-    // An empty Reserved isn't representable in the syntax
-    U_ASSERT(r.numParts() > 0);
-
-    const UnicodeString& contents = r.getPart(0).unquoted();
-    // Parts should never be empty
-    U_ASSERT(contents.length() > 0);
-
-    // Return first character of string
-    return UnicodeString(contents, 0, 1);
-}
-
 // Formats an expression using `globalEnv` for the values of variables
 [[nodiscard]] FormattedPlaceholder MessageFormatter::formatExpression(const Environment& globalEnv,
                                                                 const Expression& expr,
@@ -268,12 +250,6 @@ static UnicodeString reservedFallback (const Expression& e) {
         return {};
     }
 
-    // Formatting error
-    if (expr.isReserved()) {
-        context.getErrors().setReservedError(status);
-        return FormattedPlaceholder(reservedFallback(expr));
-    }
-
     const Operand& rand = expr.getOperand();
     // Format the operand (formatOperand handles the case of a null operand)
     FormattedPlaceholder randVal = formatOperand(globalEnv, rand, context, status);
@@ -675,12 +651,6 @@ ResolvedSelector MessageFormatter::resolveVariables(const Environment& env,
         return {};
     }
 
-    // A `reserved` is an error
-    if (expr.isReserved()) {
-        context.getErrors().setReservedError(status);
-        return ResolvedSelector(FormattedPlaceholder(reservedFallback(expr)));
-    }
-
     // Function call -- resolve the operand and options
     if (expr.isFunctionCall()) {
         const Operator* rator = expr.getOperator(status);

icu4c/source/i18n/messageformat2_checker.cpp

@@ -136,9 +136,7 @@ void Checker::addFreeVars(TypeEnvironment& t, const OptionMap& opts, UErrorCode&
 void Checker::addFreeVars(TypeEnvironment& t, const Operator& rator, UErrorCode& status) {
     CHECK_ERROR(status);
 
-    if (!rator.isReserved()) {
-        addFreeVars(t, rator.getOptionsInternal(), status);
-    }
+    addFreeVars(t, rator.getOptionsInternal(), status);
 }
 
 void Checker::addFreeVars(TypeEnvironment& t, const Expression& rhs, UErrorCode& status) {
@@ -213,12 +211,10 @@ void Checker::requireAnnotated(const TypeEnvironment& t, const Expression& selec
     if (selectorExpr.isFunctionCall()) {
         return; // No error
     }
-    if (!selectorExpr.isReserved()) {
-        const Operand& rand = selectorExpr.getOperand();
-        if (rand.isVariable()) {
-            if (t.get(rand.asVariable()) == TypeEnvironment::Type::Annotated) {
-                return; // No error
-            }
+    const Operand& rand = selectorExpr.getOperand();
+    if (rand.isVariable()) {
+        if (t.get(rand.asVariable()) == TypeEnvironment::Type::Annotated) {
+            return; // No error
         }
     }
     // If this code is reached, an error was detected
@@ -240,9 +236,6 @@ TypeEnvironment::Type typeOf(TypeEnvironment& t, const Expression& expr) {
     if (expr.isFunctionCall()) {
         return TypeEnvironment::Type::Annotated;
     }
-    if (expr.isReserved()) {
-        return TypeEnvironment::Type::Unannotated;
-    }
     const Operand& rand = expr.getOperand();
     U_ASSERT(!rand.isNull());
     if (rand.isLiteral()) {
@@ -296,11 +289,6 @@ void Checker::checkDeclarations(TypeEnvironment& t, UErrorCode& status) {
         // Next, extend the type environment with a binding from lhs to its type
         t.extend(lhs, typeOf(t, rhs), status);
     }
-
-    // Check for unsupported statements
-    if (dataModel.unsupportedStatementsLen > 0) {
-        errors.addError(StaticErrorType::UnsupportedStatementError, status);
-    }
 }
 
 void Checker::check(UErrorCode& status) {