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Further optimize the rich style of diagnostic message #19141

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78c170e
Feat Further optimize the rich style of diagnostic message
muqiuhan Dec 5, 2025
0b202e3
Merge branch 'main' into feat/enhance-diagnostic
muqiuhan Dec 5, 2025
57c1bfd
Use seq instead of resize array
muqiuhan Dec 6, 2025
bd92cbf
Add Release notes
muqiuhan Dec 6, 2025
c6fe524
reformat
muqiuhan Dec 6, 2025
ae8de2a
Merge branch 'dotnet:main' into feat/enhance-diagnostic
muqiuhan Dec 14, 2025
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4 changes: 4 additions & 0 deletions docs/release-notes/.FSharp.Compiler.Service/10.0.200.md
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Original file line number Diff line number Diff line change
Expand Up @@ -8,3 +8,7 @@
* `SynExprLetOrUseTrivia` is now `SynLetOrUseTrivia`. ([PR #19090](https://github.com/dotnet/fsharp/pull/19090))
* `SynMemberDefn.LetBindings` has trivia. ([PR #19090](https://github.com/dotnet/fsharp/pull/19090))
* `SynModuleDecl.Let` has trivia. ([PR #19090](https://github.com/dotnet/fsharp/pull/19090))

### Changed

* Improve rich diagnostic formatting. ([PR #19141](https://github.com/dotnet/fsharp/pull/19141))
106 changes: 94 additions & 12 deletions src/Compiler/Driver/CompilerDiagnostics.fs
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Expand Up @@ -2246,11 +2246,103 @@ type PhasedDiagnostic with

/// used by fsc.exe and fsi.exe, but not by VS
/// prints error and related errors to the specified StringBuilder
member diagnostic.Output(buf, tcConfig: TcConfig, severity) =
member diagnostic.Output(buf: StringBuilder, tcConfig: TcConfig, severity: FSharpDiagnosticSeverity) =

// 'true' for "canSuggestNames" is passed last here because we want to report suggestions in fsc.exe and fsi.exe, just not in regular IDE usage.
let diagnostics = CollectFormattedDiagnostics(tcConfig, severity, diagnostic, true)

let renderRich (details: FormattedDiagnosticDetailedInfo) =
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@T-Gro T-Gro Dec 11, 2025

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We have grown to a non-trivial amount of logic now.
This should now have dedicated tests showing the various aspects of the feature in place.

(as an inspiration, look how existing "help" function exercise the compiler to print help and then assert on exact matching compiler output - that might work well. Other test suites typically do not focus on the formatting of diagnostics and instead use F# data to assert them, so e.g. ComponentTests style will not be much applicable for this feature)

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@T-Gro T-Gro Dec 11, 2025

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If this does not need any environmental information and it only takes the details object, you can also consider extracting this to a separate standalone function and test it in isolation.

let severityText =
match severity with
| FSharpDiagnosticSeverity.Error -> "Error"
| FSharpDiagnosticSeverity.Warning -> "Warning"
| FSharpDiagnosticSeverity.Info
| FSharpDiagnosticSeverity.Hidden -> "Info"

let codeText = sprintf "FS%04d" details.Canonical.ErrorNumber

let messageSentences =
details.Message.Split([| '\n' |], StringSplitOptions.None)
|> Seq.collect (fun line ->
let parts = line.Split([| '.' |], StringSplitOptions.None)

parts
|> Seq.mapi (fun idx part ->
let trimmed = part.Trim()

if trimmed = "" then
None
else
let hasDot = idx < parts.Length - 1 || line.EndsWith(".")
Some(if hasDot then trimmed + "." else trimmed)))
|> Seq.choose id
|> Seq.toList

let messageLines =
match messageSentences with
| head :: tail ->
seq {
yield sprintf "[%s] %s: %s" codeText severityText head
yield! tail |> Seq.map (fun s -> sprintf "│ %s" s)
}
| [] -> seq { yield sprintf "[%s] %s" codeText details.Message }

let locationAndSnippet =
match details.Location with
| Some l when not l.IsEmpty ->
seq {
let range = l.Range

let fileDisplay =
if String.IsNullOrWhiteSpace l.File then
"unknown"
else
l.File

yield sprintf "└─ [%s:(%d,%d)]" fileDisplay range.StartLine range.StartColumn
yield ""

try
let fullPath =
l.File |> FileSystem.GetFullFilePathInDirectoryShim tcConfig.implicitIncludeDir

if FileSystem.FileExistsShim fullPath then
let content = File.ReadAllLines fullPath

if content.Length > 0 then
let startLine = max 1 (range.StartLine - 1)
let endLine = min content.Length range.StartLine

let snippetLines =
[
for ln in startLine .. min content.Length (endLine + 1) -> ln, content[ln - 1]
]

let lineNoWidth =
snippetLines
|> List.map fst
|> List.map string
|> List.map String.length
|> List.max

let caretStart = max 0 (range.StartColumn - 1)
let caretWidth = max 1 (max 0 (range.EndColumn - range.StartColumn))
let caretLine = String.make caretStart ' ' + String.make caretWidth '^'

for (ln, text) in snippetLines do
yield sprintf " %*d | %s" lineNoWidth ln text

if ln = range.StartLine then
yield sprintf " %s | %s" (String.make lineNoWidth ' ') caretLine
with _ ->
()
}
| _ -> Seq.empty

Seq.append messageLines locationAndSnippet
|> String.concat "\n"
|> fun rendered -> buf.Append(rendered) |> ignore

for e in diagnostics do
Printf.bprintf buf "\n"

Expand All @@ -2273,17 +2365,7 @@ type PhasedDiagnostic with

buf.AppendString details.Canonical.TextRepresentation
buf.AppendString details.Message
| DiagnosticStyle.Rich ->
buf.AppendString details.Canonical.TextRepresentation
buf.AppendString details.Message

match details.Location with
| Some l when not l.IsEmpty ->
buf.AppendString l.TextRepresentation

if details.Context.IsSome then
buf.AppendString details.Context.Value
| _ -> ()
| DiagnosticStyle.Rich -> renderRich details

member diagnostic.OutputContext(buf, prefix, fileLineFunction) =
match diagnostic.Range with
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