[SR-5457] Specific error message when user tries to compile Swift executable

Previous ID	SR-5457
Radar	None
Original Reporter	carlb (JIRA User)
Type	Improvement

Votes	0
Component/s	Compiler
Labels	Improvement, Parser, StarterBug
Assignee	None
Priority	Medium

md5: 111feeb80ab569e4bee27d9d511be231

Issue Description:

I was talking to a new Swift programmer who came from the ruby/python world. He had this output:

$ swift .build/debug/helloWorld
.build/debug/helloWorld:1:1: error: invalid UTF-8 found in source file
�����x� H__PAGEZERO8__TEXT@@__text__TEXT Ͷ �__stubs__TEXT��
.build/debug/helloWorld:1:2: error: invalid UTF-8 found in source file
�����x� H__PAGEZERO8__TEXT@@__text__TEXT Ͷ �__stubs__TEXT��
.build/debug/helloWorld:1:3: error: invalid UTF-8 found in source file
�����x� H__PAGEZERO8__TEXT@@__text__TEXT Ͷ �__stubs__TEXT��
.build/debug/helloWorld:1:4: error: input files must be encoded as UTF-8 instead of UTF-16
�����x� H__PAGEZERO8__TEXT@@__text__TEXT Ͷ �__stubs__TEXT��

Because he had started with Swift scripts, where you put swift in front of the file.swift name.

The error message above is perfectly valid, but unhelpful in this case. I would guess enough new programmers would make this mistake that it's worth discussing a special-case error message if the file to be run is already a Swift executable.