Diagnostics: Clearer information style

src/Compiler/Driver/CompilerDiagnostics.fs

@@ -2039,14 +2039,15 @@ type FormattedDiagnosticDetailedInfo =
         Location: FormattedDiagnosticLocation option
         Canonical: FormattedDiagnosticCanonicalInformation
         Message: string
+        Context: string option
     }
 
 [<RequireQualifiedAccess>]
 type FormattedDiagnostic =
     | Short of FSharpDiagnosticSeverity * string
     | Long of FSharpDiagnosticSeverity * FormattedDiagnosticDetailedInfo
 
-let FormatDiagnosticLocation (tcConfig: TcConfig) m : FormattedDiagnosticLocation =
+let FormatDiagnosticLocation (tcConfig: TcConfig) (m: Range) : FormattedDiagnosticLocation =
     if equals m rangeStartup || equals m rangeCmdArgs then
         {
             Range = m
@@ -2073,7 +2074,7 @@ let FormatDiagnosticLocation (tcConfig: TcConfig) m : FormattedDiagnosticLocatio
             | DiagnosticStyle.Default ->
                 let file = file.Replace('/', Path.DirectorySeparatorChar)
                 let m = withStart (mkPos m.StartLine (m.StartColumn + 1)) m
-                (sprintf "%s(%d,%d): " file m.StartLine m.StartColumn), m, file
+                (sprintf "◦→ %s (%d,%d)" file m.StartLine m.StartColumn), m, file
 
             // We may also want to change Test to be 1-based
             | DiagnosticStyle.Test ->
@@ -2150,7 +2151,7 @@ let CollectFormattedDiagnostics (tcConfig: TcConfig, severity: FSharpDiagnosticS
                 match tcConfig.diagnosticStyle with
                 // Show the subcategory for --vserrors so that we can fish it out in Visual Studio and use it to determine error stickiness.
                 | DiagnosticStyle.VisualStudio -> sprintf "%s %s FS%04d: " subcategory message errorNumber
-                | _ -> sprintf "%s FS%04d: " message errorNumber
+                | _ -> sprintf "\n◦→ %s FS%04d: " message errorNumber
 
             let canonical: FormattedDiagnosticCanonicalInformation =
                 {
@@ -2159,11 +2160,37 @@ let CollectFormattedDiagnostics (tcConfig: TcConfig, severity: FSharpDiagnosticS
                     TextRepresentation = text
                 }
 
-            let message = diagnostic.FormatCore(tcConfig.flatErrors, suggestNames)
+            let message =
+                diagnostic.FormatCore(tcConfig.flatErrors, suggestNames).Split([| '\n' |])
+                |> Array.map (fun msg -> "\n◦   " + msg)
+                |> String.Concat
+
+            let context =
+                match diagnostic.Range with
+                | Some m ->
+                    let content =
+                        m.FileName
+                        |> FileSystem.GetFullFilePathInDirectoryShim tcConfig.implicitIncludeDir
+                        |> System.IO.File.ReadAllLines
+
+                    if m.StartLine = m.EndLine then
+                        $"\n◦ {m.StartLine} |{content[m.StartLine - 1]}\n"
+                        + $"""◦ {String.init (m.StartColumn + 3) (fun _ -> " ")}^{String.init (m.EndColumn - m.StartColumn) (fun _ -> "~")}"""
+                        |> Some
+                    else
+                        None
+                // Untested multi-line support:
+                //    content
+                //    |> fun lines -> Array.sub lines (m.StartLine - 1) (m.EndLine - m.StartLine - 1)
+                //    |> Array.fold (fun (context, lineNumber) line -> (context + $"\n◦ {lineNumber} |{line}", lineNumber + 1)) ("", (m.StartLine))
+                //    |> fst
+                //    |> Some
+                | None -> None
 
             let entry: FormattedDiagnosticDetailedInfo =
                 {
                     Location = where
+                    Context = context
                     Canonical = canonical
                     Message = message
                 }
@@ -2194,7 +2221,10 @@ type PhasedDiagnostic with
             | FormattedDiagnostic.Short(_, txt) -> buf.AppendString txt
             | FormattedDiagnostic.Long(_, details) ->
                 match details.Location with
-                | Some l when not l.IsEmpty -> buf.AppendString l.TextRepresentation
+                | Some l when not l.IsEmpty ->
+                    buf.AppendString l.TextRepresentation
+                    // Because details.Context depends on the value of details.Location, if details.Location is not None, details.Context can be accessed directly.
+                    buf.AppendString details.Context.Value
                 | _ -> ()
 
                 buf.AppendString details.Canonical.TextRepresentation

src/Compiler/Driver/CompilerDiagnostics.fsi

@@ -113,7 +113,8 @@ type FormattedDiagnosticCanonicalInformation =
 type FormattedDiagnosticDetailedInfo =
     { Location: FormattedDiagnosticLocation option
       Canonical: FormattedDiagnosticCanonicalInformation
-      Message: string }
+      Message: string
+      Context: string option }
 
 /// Used internally and in LegacyHostedCompilerForTesting
 [<RequireQualifiedAccess>]