Gracefully handle 'catch' and 'finally' blocks without a preceding 'try' block.

Fixes #216.

As a note of this fix, when a 'catch' block is followed by a 'finally' block, only the 'catch' keyword gets an error reported on it.

src/compiler/diagnosticInformationMap.generated.ts

@@ -160,6 +160,8 @@ module ts {
         Constructor_implementation_expected: { code: 2240, category: DiagnosticCategory.Error, key: "Constructor implementation expected." },
         An_export_assignment_cannot_be_used_in_a_module_with_other_exported_elements: { code: 2245, category: DiagnosticCategory.Error, key: "An export assignment cannot be used in a module with other exported elements." },
         A_parameter_property_is_only_allowed_in_a_constructor_implementation: { code: 2246, category: DiagnosticCategory.Error, key: "A parameter property is only allowed in a constructor implementation." },
+        A_catch_clause_must_be_preceded_by_a_try_statement: { code: 2249, category: DiagnosticCategory.Error, key: "A 'catch' clause must be preceded by a 'try' statement." },
+        A_finally_block_must_be_preceded_by_a_try_statement: { code: 2250, category: DiagnosticCategory.Error, key: "A 'finally' block must be preceded by a 'try' statement." },
         Circular_definition_of_import_alias_0: { code: 3000, category: DiagnosticCategory.Error, key: "Circular definition of import alias '{0}'." },
         Cannot_find_name_0: { code: 3001, category: DiagnosticCategory.Error, key: "Cannot find name '{0}'." },
         Module_0_has_no_exported_member_1: { code: 3002, category: DiagnosticCategory.Error, key: "Module '{0}' has no exported member '{1}'." },

src/compiler/diagnosticMessages.json

@@ -632,6 +632,15 @@
         "category": "Error",
         "code": 2246
     },
+    "A 'catch' clause must be preceded by a 'try' statement.": {
+        "category": "Error",
+        "code": 2249
+    },
+    "A 'finally' block must be preceded by a 'try' statement.": {
+        "category": "Error",
+        "code": 2250
+    },
+
     "Circular definition of import alias '{0}'.": {
         "category": "Error",
         "code": 3000

src/compiler/parser.ts

@@ -2542,6 +2542,35 @@ module ts {
             return finishNode(node);
         }
 
+        // This function is used for parsing 'catch'/'finally' blocks
+        // in spite of them missing a 'try' statement.
+        function parseCatchOrFinallyBlocksMissingTryStatement(): TryStatement {
+
+            Debug.assert(token === SyntaxKind.CatchKeyword || token === SyntaxKind.FinallyKeyword,
+                "'parseCatchOrFinallyBlocksMissingTryStatement' should only be called when the current token is a 'catch' or 'finally' keyword.");
+
+            // We're just going to return a bogus TryStatement.
+            var node = <TryStatement>createNode(SyntaxKind.TryStatement);
+            node.tryBlock = <Block>createNode(SyntaxKind.Block);
+            node.tryBlock.statements = createMissingList<Statement>();
+
+            if (token === SyntaxKind.CatchKeyword) {
+                error(Diagnostics.A_catch_clause_must_be_preceded_by_a_try_statement);
+                node.catchBlock = parseCatchBlock();
+            }
+
+            if (token === SyntaxKind.FinallyKeyword) {
+                // Only report an error on the 'finally' block if we haven't on the 'catch' block.
+                if (node.catchBlock === undefined) {
+                    error(Diagnostics.A_finally_block_must_be_preceded_by_a_try_statement);
+                }
+
+                node.finallyBlock = parseTokenAndBlock(SyntaxKind.FinallyKeyword, SyntaxKind.FinallyBlock);
+            }
+
+            return finishNode(node);
+        }
+
         function parseTokenAndBlock(token: SyntaxKind, kind: SyntaxKind): Block {
             var pos = getNodePos();
             parseExpected(token);
@@ -2646,6 +2675,10 @@ module ts {
                 case SyntaxKind.ThrowKeyword:
                 case SyntaxKind.TryKeyword:
                 case SyntaxKind.DebuggerKeyword:
+                // 'catch' and 'finally' do not actually indicate that the code is part of a statement,
+                // however, we say they are here so that we may gracefully parse them and error later.
+                case SyntaxKind.CatchKeyword:
+                case SyntaxKind.FinallyKeyword:
                     return true;
                 case SyntaxKind.InterfaceKeyword:
                 case SyntaxKind.ClassKeyword:
@@ -2653,13 +2686,17 @@ module ts {
                 case SyntaxKind.EnumKeyword:
                     // When followed by an identifier, these do not start a statement but might
                     // instead be following declarations
-                    if (isDeclaration()) return false;
+                    if (isDeclaration()) {
+                        return false;
+                    }
                 case SyntaxKind.PublicKeyword:
                 case SyntaxKind.PrivateKeyword:
                 case SyntaxKind.StaticKeyword:
                     // When followed by an identifier or keyword, these do not start a statement but
                     // might instead be following type members
-                    if (lookAhead(() => nextToken() >= SyntaxKind.Identifier)) return false;
+                    if (lookAhead(() => nextToken() >= SyntaxKind.Identifier)) {
+                        return false;
+                    }
                 default:
                     return isExpression();
             }
@@ -2697,6 +2734,9 @@ module ts {
                     return parseThrowStatement();
                 case SyntaxKind.TryKeyword:
                     return parseTryStatement();
+                case SyntaxKind.CatchKeyword:
+                case SyntaxKind.FinallyKeyword:
+                    return parseCatchOrFinallyBlocksMissingTryStatement();
                 case SyntaxKind.DebuggerKeyword:
                     return parseDebuggerStatement();
                 default:

tests/baselines/reference/invalidTryStatements2.errors.txt

@@ -1,4 +1,4 @@
-==== tests/cases/conformance/statements/tryStatements/invalidTryStatements2.ts (4 errors) ====
+==== tests/cases/conformance/statements/tryStatements/invalidTryStatements2.ts (2 errors) ====
     function fn() {
         try {
         } catch { // syntax error, missing '(x)'
@@ -8,11 +8,7 @@
     
         catch(x) { } // error missing try
         ~~~~~
-!!! Statement expected.
-                 ~
-!!! '=>' expected.
+!!! A 'catch' clause must be preceded by a 'try' statement.
     
         finally{ } // error missing try
-        ~~~~~~~
-!!! Statement expected.
     }

tests/baselines/reference/parserMissingToken1.errors.txt

@@ -1,6 +1,8 @@
-==== tests/cases/conformance/parser/ecmascript5/MissingTokens/parserMissingToken1.ts (2 errors) ====
+==== tests/cases/conformance/parser/ecmascript5/MissingTokens/parserMissingToken1.ts (3 errors) ====
     a / finally
         ~~~~~~~
 !!! Expression expected.
+               
+!!! '{' expected.
     ~
 !!! Cannot find name 'a'.