Fantomas inserts space that breaks index lookups (without a dot)

[dbrattli]

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?}

[nojaf]

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]

🤖 This is an automated response from Repo Assist.

Good news: I tested this with the current main branch and the bug appears to have been fixed! The following now formats correctly:

let test (dict: System.Collections.Generic.IDictionary(string, unit -) unit -> unit>) =
    let key = "foo"
    dict[ key ] () ()

Formatted output (current main):

let test (dict: System.Collections.Generic.IDictionary(string, unit -) unit -> unit>) =
    let key = "foo"
    dict[key] () ()

No extra space is inserted before [key] even with multiple subsequent arguments. If you're still seeing this issue with a recent Fantomas version, please re-open with the version number and a fresh reproduction. Otherwise this could be closed as resolved!

Generated by Repo Assist · ◷

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[nojaf]

/repo-assist which PR fixed this? We can close this as duplicate of another issue.

[github-actions]

🤖 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 App active pattern was flattening through IndexWithoutDot expressions and losing the no-space semantics, causing expr[idx] () () to become expr [ idx ] () () when multiple arguments followed the indexer.

Happy to close this as resolved by that PR!

Generated by Repo Assist for issue #2519 · ◷

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[nojaf]

/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)