fsprojects
Idempotency problem when using a list with interpolated strings
Issue created from fantomas-online
Before formatting, code was compiling:
let f hdrKey =
readOnlyDict[$"{hdrKey}:0", "X-MessageID"
$"{hdrKey}:1", "Authorization"]
Formatted code
let f hdrKey =
readOnlyDict[$"{hdrKey}:0", "X-MessageID"
$"{hdrKey}:1", "Authorization"]
Reformatted code (note the missing semicolon!)
let f hdrKey =
readOnlyDict[$"{hdrKey}:0", "X-MessageID" $"{hdrKey}:1", "Authorization"]
Problem description
Fantomas was not able to produce the same code after reformatting the result.
Extra information
- [x] The formatted result breaks my code.
- [x] The formatted result gives compiler ~warnings~ errors.
- [x] I or my company would be willing to help fix this.
Options
Fantomas master branch at 2022-05-09T12:59:04Z - f2e3c0898acc865e05bb3d94510daadf797a234c
Default Fantomas configuration
- I've seen this fail with Fantomas 4.7.0
- Exactly the same code with VS 2022 Extension uses Fantomas 4.6.0 and succeeds and leaves the code as-is
- In other words, seems to be a regression.
Did you know that you can ignore files when formatting from fantomas-tool or the FAKE targets by using a .fantomasignore file? yes ;).
Alternative, failing code:
let f x = readOnlyDict[$"{x}:0", ""; $"{x}:1", ""]
After formatting, breaks:
let f x =
readOnlyDict[$"{x}:0", ""
$"{x}:1", ""]
This seems related to #2201, where it was suggested that adding a space before the list bracket fixes Fantomas' handling. However, in many cases adding a space will break the code, as f x[] is not equal to f x [] in F#.
Hello, thank you for raising this. I left feedback on how to fix this in #2158. Are you interested in submitting a PR?
In other words, seems to be a regression.
That is debatable btw. In F# 6 the new indexer syntax recontextualizes what you wrote.
> readOnlyDict;;
val it:
(seq<'a * 'b> -> Collections.Generic.IReadOnlyDictionary<'a,'b>)
when 'a: equality
readOnlyDictis a function call, so it is weird that you are trying to index into it with the $"{x}:0", ""; $"{x}:1", "" expression. Fantomas does not know what your code is doing, so it saw an index expression and restored it as such.
The only bug I see here is how it is wrongly handling a multiline expression inside the index.
That is debatable btw. In F# 6 the new indexer syntax recontextualizes what you wrote.
@nojaf Well, I mentioned that after the observation that Fantomas 4.6 tackles this code correctly somehow. The project is F# 6.0 indeed, but running it with commandline Fantomas 4.7 showed the problem.
so it is weird that you are trying to index into it with the
$"{x}:0", ""; $"{x}:1", ""expression.
This is an interesting observation. I didn't consider this. So I tried a few things in F# Interactive, and I get a compile error each time, esp. w.r.t. it being an indexed property.
But, in the "normal" .fs file, it gets compiled just fine. Here's what I simplified it to, which compiles fine in a .NET 6.0 project, but does NOT compile when send to Interactive:
let configureCorsPolicy x = Seq.iter ignore x
let hdrKey = "foo"
configureCorsPolicy
readOnlyDict[$"{hdrKey}:0", "X-MessageID"; $"{hdrKey}:1", "Authorization"]
I thought this was similar to the subtle difference between g().ToString() and g ().ToString(), but it seems it is something else entirely.
Sorry, I stand corrected. It wasn't an error in FSI, it was a warning:
info FS3365: The syntax 'expr1[expr2]' is used for indexing. Consider adding a type annotation to enable indexing, or if calling a function add a space, e.g. 'expr1 [expr2]'.
Darn, and now I notice the #nowarn "3365". We need to get rid of that!
The compiler is a bit weird here. I removed the #nowarn, upped the warning level to 5, but it doesn't report on it, except for in the editor itself when hovering. This is odd, since I did get the warning with a slightly different syntax.
That's clearly F# compiler territory and not so much Fantomas territory.
I might have a look one of these days in submitting a PR to fix the underlying bug where the alignment gets screwed up in multiline statements.
The compiler is a bit weird here
Well, one other thing to note is that Fantomas is using a slightly newer version of the compiler bits. In the past, we referenced the FCS from NuGet, so depending on your .NET SDK version, there might be a difference there.
For a few days now, we are using our own FCS version, which is tied closely to the main branch of dotnet/fsharp. (See https://github.com/fsprojects/fantomas/issues/2217).
All of this isn't really a problem unless there are some more significant changes like the new index syntax.
I might have a look one of these days in submitting a PR to fix the underlying bug where the alignment gets screwed up in multiline statements.
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