Rename exception var when local var has the same name.

docs/exceptions.md

@@ -1,5 +1,6 @@
 # Exceptions
 ## Omitting the exception variable
+### Standard use case
 There are times where you don't need to use the exception variable in a try/catch. BrighterScript allows you to omit the variable. At transpile time, we'll inject a variable so that your output is still valid brightscript
 
 ```BrighterScript
@@ -23,3 +24,28 @@ function init()
     end try
 end function
 ```
+
+### Exception variable name collision
+By default, bsc will name the omitted variable `e`. However, if you've already got a variable named `e` in your function body, we'll get out of your way and name it `__bsc_error` instead.
+
+```BrighterScript
+function init()
+    try
+        somethingDangerous()
+    catch
+        print "I live on the edge"
+    end try
+end function
+```
+
+transpiles to
+
+```BrighterScript
+function init()
+    try
+        somethingDangerous()
+    catch __bsc_error
+        print "I live on the edge"
+    end try
+end function
+```

docs/readme.md

@@ -50,6 +50,15 @@ enum RemoteButton
 end enum
 ```
 
+## [Exceptions](exceptions.md)
+```brighterscript
+try
+    somethingDangerous()
+catch 'look, no exception variable!
+    print "Living on the edge!"
+end try
+```
+
 ## [Namespaces](namespaces.md)
 ```brighterscript
 namespace util
@@ -133,4 +142,4 @@ end sub
 ```
 
 ## [Variable Shadowing](variable-shadowing.md)
-Name resolution rules for various types of shadowing.
+Name resolution rules for various types of shadowing.

src/files/BrsFile.spec.ts

@@ -2213,6 +2213,28 @@ describe('BrsFile', () => {
                     end sub
                 `, undefined, 'source/main.bs');
             });
+
+            it('uses alternate name when `e` is already a local var', async () => {
+                await testTranspile(`
+                    sub new()
+                        e = "ello love"
+                        try
+                            print "hello"
+                        catch
+                            print "error"
+                        end try
+                    end sub
+                `, `
+                    sub new()
+                        e = "ello love"
+                        try
+                            print "hello"
+                        catch __bsc_error
+                            print "error"
+                        end try
+                    end sub
+                `, undefined, 'source/main.bs');
+            });
         });
 
         describe('namespaces', () => {

src/parser/Statement.ts

@@ -3141,7 +3141,12 @@ export class CatchStatement extends Statement {
         return [
             state.transpileToken(this.tokens.catch, 'catch'),
             ' ',
-            this.exceptionVariableExpression?.transpile(state) ?? ['e'],
+            this.exceptionVariableExpression?.transpile(state) ?? [
+                //use the variable named `e` if it doesn't exist in this function body. otherwise use '__bsc_error' just to make sure we're out of the way
+                this.getSymbolTable()?.hasSymbol('e', SymbolTypeFlag.runtime)
+                    ? '__bsc_error'
+                    : 'e'
+            ],
             ...(this.catchBranch?.transpile(state) ?? [])
         ];
     }