feat(lex): Emit try/catch/throw lexemes for parsing

RBI 9.4 adds support for error handling via the `try`/`catch` model [1].
Interestingly, `try`, `catch`, and `endtry` are all valid identifiers!
That makes parsing a little bit tougher, but it's not unprecedented in
this language.  Detect `try`/`catch`/throw`/`end try` during lexing and
emit the proper lexemes.

[1] https://developer.roku.com/docs/references/brightscript/language/error-handling.html
see #554

src/lexer/Lexeme.ts

@@ -68,6 +68,7 @@ export enum Lexeme {
     // canonical source: https://sdkdocs.roku.com/display/sdkdoc/Reserved+Words
     And = "And",
     Box = "Box",
+    Catch = "Catch",
     CreateObject = "CreateObject",
     Dim = "Dim",
     Else = "Else",
@@ -77,6 +78,7 @@ export enum Lexeme {
     EndFor = "EndFor",
     EndIf = "EndIf",
     EndSub = "EndSub",
+    EndTry = "EndTry",
     EndWhile = "EndWhile",
     Eval = "Eval",
     Exit = "Exit",
@@ -105,8 +107,10 @@ export enum Lexeme {
     Stop = "Stop",
     Sub = "Sub",
     Tab = "Tab",
+    Throw = "Throw",
     To = "To",
     True = "True",
+    Try = "Try",
     Type = "Type",
     While = "While",
 

src/lexer/ReservedWords.ts

@@ -2,7 +2,7 @@ import { Lexeme as L } from "./Lexeme";
 
 /**
  * The set of all reserved words in the reference BrightScript runtime. These can't be used for any
- * other purpose within a BrightScript file.
+ * other purpose (e.g. as identifiers) within a BrightScript file.
  * @see https://sdkdocs.roku.com/display/sdkdoc/Reserved+Words
  */
 export const ReservedWords = new Set([
@@ -44,14 +44,15 @@ export const ReservedWords = new Set([
     "tab",
     "then",
     "to",
+    "throw",
     "true",
     "type",
     "while",
 ]);
 
 /**
  * The set of keywords in the reference BrightScript runtime. Any of these that *are not* reserved
- * words can be used within a BrightScript file for other purposes, e.g. `tab`.
+ * words can be used within a BrightScript file for other purposes as identifiers, e.g. `tab`.
  *
  * Unfortunately there's no canonical source for this!
  */
@@ -69,6 +70,7 @@ export const KeyWords: { [key: string]: L } = {
     "end if": L.EndIf,
     endsub: L.EndSub,
     "end sub": L.EndSub,
+    "end try": L.EndTry, // note: 'endtry' (no space) is *not* a keyword
     endwhile: L.EndWhile,
     "end while": L.EndWhile,
     exit: L.Exit,
@@ -94,6 +96,7 @@ export const KeyWords: { [key: string]: L } = {
     stop: L.Stop,
     sub: L.Sub,
     to: L.To,
+    throw: L.Throw,
     true: L.True,
     while: L.While,
 };

test/lexer/Lexer.test.js

@@ -248,8 +248,8 @@ describe("lexer", () => {
     describe("identifiers", () => {
         it("matches single-word keywords", () => {
             // test just a sample of single-word reserved words for now.
-            // if we find any that we've missed
-            let { tokens } = Lexer.scan("and or if else endif return true false line_num");
+            // if we find any that we've missed, add them here
+            let { tokens } = Lexer.scan("and or if else endif return true false line_num throw");
             expect(tokens.map((w) => w.kind)).toEqual([
                 Lexeme.And,
                 Lexeme.Or,
@@ -260,20 +260,24 @@ describe("lexer", () => {
                 Lexeme.True,
                 Lexeme.False,
                 Lexeme.Identifier,
+                Lexeme.Throw,
                 Lexeme.Eof,
             ]);
             expect(tokens.filter((w) => !!w.literal).length).toBe(0);
         });
 
         it("matches multi-word keywords", () => {
-            let { tokens } = Lexer.scan("else if end if end while End Sub end Function Exit wHILe");
+            let { tokens } = Lexer.scan(
+                "else if end if end while End Sub end Function Exit wHILe end try"
+            );
             expect(tokens.map((w) => w.kind)).toEqual([
                 Lexeme.ElseIf,
                 Lexeme.EndIf,
                 Lexeme.EndWhile,
                 Lexeme.EndSub,
                 Lexeme.EndFunction,
                 Lexeme.ExitWhile,
+                Lexeme.EndTry,
                 Lexeme.Eof,
             ]);
             expect(tokens.filter((w) => !!w.literal).length).toBe(0);
@@ -288,6 +292,18 @@ describe("lexer", () => {
             ]);
         });
 
+        it("reads try/catch/throw properly", () => {
+            let { tokens } = Lexer.scan("try catch throw end try endtry");
+            expect(tokens.map((w) => w.kind)).toEqual([
+                Lexeme.Identifier, // try
+                Lexeme.Identifier, // catch
+                Lexeme.Throw, // throw
+                Lexeme.EndTry, // end try
+                Lexeme.Identifier, // endtry
+                Lexeme.Eof,
+            ]);
+        });
+
         it("matches keywords with silly capitalization", () => {
             let { tokens } = Lexer.scan("iF ELSE eNDIf FUncTioN");
             expect(tokens.map((w) => w.kind)).toEqual([