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Fantomas inserts space that breaks index lookups (without a dot) #2519
Description
Issue created from fantomas-online
Code
let test (negotiationRules: IDictionary<string, unit -> unit -> unit>) =
let mimeType = "foo"
negotiationRules[ mimeType ] () ()Result
let test (negotiationRules: IDictionary<string, unit -> unit -> unit>) =
let mimeType = "foo"
negotiationRules [ mimeType ] () ()
Problem description
Fantomas inserts extra space between i.e negotiationRules and the [...] which breaks the code. This seems to happen if there are more than one argument after e.g negotiationRules [ mimeType ] () will be formatted correctly whiles negotiationRules [ mimeType ] () () will not.
The example is a simplified version of: https://github.com/dbrattli/Fable.Giraffe/blob/main/src/Negotiation.fs#L131
Extra information
- The formatted result breaks my code.
- The formatted result gives compiler warnings.
- I or my company would be willing to help fix this.
Options
Fantomas master branch at 2022-09-17T05:39:07Z - c1a99d4
Default Fantomas configuration
Did you know that you can ignore files when formatting from fantomas-tool or the FAKE targets by using a .fantomasignore file?
Activity
nojaf commentedon Sep 19, 2022
Hello, this is a tricky one to fix I think.
Interestingly enough, the problem doesn't occur when one of the arguments is indexed. (sample).
As a workaround you can use the dot notation
negotiationRules.[mimeType] () ()or submit a PR to fix this.github-actions commentedon Mar 14, 2026
nojaf commentedon Mar 16, 2026
/repo-assist which PR fixed this? We can close this as duplicate of another issue.
github-actions commentedon Mar 16, 2026
🤖 This is an automated response from Repo Assist.
This was fixed by PR #3259 ("Fix index-without-dot followed by application arguments"), merged on 2026-03-09 and included in
8.0.0-alpha-005.The root cause described in that PR matches exactly: the
Appactive pattern was flattening throughIndexWithoutDotexpressions and losing the no-space semantics, causingexpr[idx] () ()to becomeexpr [ idx ] () ()when multiple arguments followed the indexer.Happy to close this as resolved by that PR!
nojaf commentedon Mar 16, 2026
/repo-assist okay, add another regression test for this specific report. Include in changelog but in unreleased section (even if that is technically not 100% accurate)
Add regression test for index-without-dot with variable key and unit …
Add regression test for index-without-dot with variable key and unit …
Merge pull request #3311 from fsprojects/repo-assist/regression-test-…
Bump the dotnet-sidecars group with 6 updates (#257)
Bump the packages group with 5 updates (#106)
Bump the packages group with 6 updates (#84)