Merge pull request #262 from Microsoft/trylessCatchesFinallyParseNicely

Improved errors for 'catch'/'finally' blocks missing 'try' statements

Author: DanielRosenwasser

src/compiler/diagnosticMessages.json

@@ -1271,4 +1271,4 @@
         "category": "Error",
         "code": -9999999
     }
-}
+}

src/compiler/parser.ts

@@ -2665,20 +2665,28 @@ 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:
                 case SyntaxKind.ModuleKeyword:
                 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();
             }
@@ -2715,6 +2723,9 @@ module ts {
                 case SyntaxKind.ThrowKeyword:
                     return parseThrowStatement();
                 case SyntaxKind.TryKeyword:
+                // Include the next two for error recovery.
+                case SyntaxKind.CatchKeyword:
+                case SyntaxKind.FinallyKeyword:
                     return parseTryStatement();
                 case SyntaxKind.DebuggerKeyword:
                     return parseDebuggerStatement();

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 (6 errors) ====
     function fn() {
         try {
         } catch { // syntax error, missing '(x)'
@@ -8,11 +8,34 @@
 
         catch(x) { } // error missing try
         ~~~~~
-!!! Statement expected.
-                 ~
-!!! '=>' expected.
+!!! 'try' expected.
 
-        finally{ } // error missing try
+        finally{ } // potential error; can be absorbed by the 'catch'
+    }
+    
+    function fn2() {
+        finally { } // error missing try
+        ~~~~~~~
+!!! 'try' expected.
+        catch (x) { } // error missing try
+        ~~~~~
+!!! 'try' expected.
+    
+        // no error
+        try {
+        }
+        finally {
+        }
+    
+        // error missing try
+        finally {
         ~~~~~~~
-!!! Statement expected.
+!!! 'try' expected.
+        }
+    
+        // error missing try
+        catch (x) {
+        ~~~~~
+!!! 'try' 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'.

tests/cases/conformance/statements/tryStatements/invalidTryStatements2.ts

@@ -5,5 +5,24 @@ function fn() {
 
     catch(x) { } // error missing try
 
-    finally{ } // error missing try
+    finally{ } // potential error; can be absorbed by the 'catch'
+}
+
+function fn2() {
+    finally { } // error missing try
+    catch (x) { } // error missing try
+
+    // no error
+    try {
+    }
+    finally {
+    }
+
+    // error missing try
+    finally {
+    }
+
+    // error missing try
+    catch (x) {
+    }
 }