Fatal error: editor placeholder in source file

[HassanTaleb90]

Run swift-format on this source:

switch <#value#> {
case <#pattern#>:
	<#code#>
default:
	<#code#>
}

I get the following errors:
1:8: editor placeholder in source file
2:6: editor placeholder in source file
3:5: editor placeholder in source file
5:5: editor placeholder in source file

Note: These errors should just be warnings and shouldn't affect the formatting of code (like Xcode does).

[HassanTaleb90]

cc @ahoppen

[ahoppen]

Having an editor placeholder in a source file should generally be considered an error because the code won’t compile. swift-format could downgrade these errors to warnings as in swiftlang/swift#64382.