[Repo Assist] fix: show hover documentation for FSI hash directives (#r, #load, #nowarn, etc.) (#1504)

* fix: show hover documentation for FSI hash directives (#r, #load, #nowarn, etc.)

Resolves #1225

## Root Cause

Hovering over a hash directive like `#r`, `#load`, `#nowarn` returned `None`
for two reasons:
1. `Lexer.findLongIdents` returns `None` for multi-character directives like
   `#nowarn` because the F# tokenizer emits them as directive tokens, not plain
   identifier tokens.
2. Even for short directives like `#r` where an identifier IS found, there was
   no lookup in the hash-directive description table.

## Fix

- Added `hashDirectiveTooltips` to `KeywordList.fs`: a dictionary mapping each
  hash directive key (e.g. `"nowarn"`) to a synthetic `ToolTipText` built from
  the existing `hashDirectives` descriptions already used for completion.
- In `TryGetToolTipEnhanced` (`ParseAndCheckResults.fs`): when
  `findLongIdents` returns `None`, check whether the line starts with a `#`
  and the cursor is within the directive keyword; if so, return the tooltip from
  `hashDirectiveTooltips`.
- Also added a fallback in the `| _ ->` branch (when `findLongIdents` finds an
  ident but it is not a keyword) to handle short directives like `#r` and `#I`.

## Test

Added `#nowarn "40"` to the tooltip test script and a `verifyDescription`
assertion that hovering on column 3 of that line returns the expected
`"Disables a compiler warning or warnings"` description.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* ci: trigger checks

---------

Co-authored-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: github-actions[bot]

src/FsAutoComplete.Core/KeywordList.fs

@@ -42,6 +42,22 @@ module KeywordList =
       "line", "Indicates the original source code line" ]
     |> dict
 
+  let hashDirectiveTooltips =
+    hashDirectives
+    |> Seq.map (fun kv ->
+      let lines = kv.Value.Replace("\r\n", "\n").Split('\n')
+      let allLines = Array.concat [| [| "<summary>" |]; lines; [| "</summary>" |] |]
+
+      let tip =
+        ToolTipText
+          [ ToolTipElement.Single(
+              [| TaggedText.tagText ("#" + kv.Key) |],
+              FSharpXmlDoc.FromXmlText(FSharp.Compiler.Xml.XmlDoc(allLines, Range.Zero))
+            ) ]
+
+      kv.Key, tip)
+    |> dict
+
   let hashSymbolCompletionItems =
     hashDirectives
     |> Seq.map (fun kv ->

src/FsAutoComplete.Core/ParseAndCheckResults.fs

@@ -357,8 +357,38 @@ type ParseAndCheckResults
     | Completion.Context.Unknown ->
       match Lexer.findLongIdents (uint32 pos.Column, lineStr) with
       | None ->
-        logger.info (Log.setMessageI $"Cannot find ident for tooltip: {pos.Column:column} in {lineStr:lineString}")
-        None
+        // Check if we're hovering over a hash directive (e.g. #r, #load, #nowarn).
+        // Lexer.findLongIdents returns None for multi-character directives like #nowarn because
+        // the F# tokenizer emits them as directive tokens, not plain identifiers.
+        let trimmedLine = lineStr.TrimStart()
+
+        if trimmedLine.StartsWith("#") then
+          let leadingSpaces = lineStr.Length - trimmedLine.Length
+          let rest = trimmedLine.Substring(1)
+          let wordEnd = rest.IndexOfAny([| ' '; '\t'; '"'; '\r'; '\n' |])
+          let directiveWord = if wordEnd > 0 then rest.[.. wordEnd - 1] else rest
+          let directiveEndCol = leadingSpaces + 1 + directiveWord.Length
+
+          if pos.Column < directiveEndCol then
+            match KeywordList.hashDirectiveTooltips.TryGetValue directiveWord with
+            | true, tip ->
+              { ToolTipText = tip
+                Signature = "#" + directiveWord
+                Footer = ""
+                SymbolInfo = TryGetToolTipEnhancedResult.Keyword directiveWord }
+              |> Some
+            | _ ->
+              logger.info (
+                Log.setMessageI $"Cannot find ident for tooltip: {pos.Column:column} in {lineStr:lineString}"
+              )
+
+              None
+          else
+            logger.info (Log.setMessageI $"Cannot find ident for tooltip: {pos.Column:column} in {lineStr:lineString}")
+            None
+        else
+          logger.info (Log.setMessageI $"Cannot find ident for tooltip: {pos.Column:column} in {lineStr:lineString}")
+          None
       | Some(col, identIsland) ->
         let identIsland = Array.toList identIsland
         // TODO: Display other tooltip types, for example for strings or comments where appropriate
@@ -380,11 +410,22 @@ type ParseAndCheckResults
                 SymbolInfo = TryGetToolTipEnhancedResult.Keyword ident }
               |> Some
             | _ ->
-              logger.info (
-                Log.setMessageI $"Cannot find ident for tooltip: {pos.Column:column} in {lineStr:lineString}"
-              )
+              // Check if we're hovering over a hash directive (e.g., #r, #load, #nowarn)
+              let trimmedLine = lineStr.TrimStart()
+
+              match KeywordList.hashDirectiveTooltips.TryGetValue ident with
+              | true, tip when trimmedLine.StartsWith("#" + ident) ->
+                { ToolTipText = tip
+                  Signature = "#" + ident
+                  Footer = ""
+                  SymbolInfo = TryGetToolTipEnhancedResult.Keyword ident }
+                |> Some
+              | _ ->
+                logger.info (
+                  Log.setMessageI $"Cannot find ident for tooltip: {pos.Column:column} in {lineStr:lineString}"
+                )
 
-              None
+                None
           | _ ->
             logger.info (Log.setMessageI $"Cannot find ident for tooltip: {pos.Column:column} in {lineStr:lineString}")
             None

test/FsAutoComplete.Tests.Lsp/CoreTests.fs

@@ -624,7 +624,18 @@ let tooltipTests state =
             5u
             (concatLines [ "type MultiArgDelegate ="; "   delegate of a: string * b: int -> bool" ])
 
-          verifySignature 120u 5u (concatLines [ "type UnannotatedDelegate ="; "   delegate of string -> int" ]) ] ]
+          verifySignature 120u 5u (concatLines [ "type UnannotatedDelegate ="; "   delegate of string -> int" ])
+
+          // FSI hash directive hover — regression for issue #1225.
+          // Hovering on a hash directive (e.g. #nowarn, #r, #load) should show documentation.
+          verifyDescription
+            123u
+            3u
+            [ "**Description**"
+              ""
+              ""
+              "Disables a compiler warning or warnings"
+              "" ] ] ]
 
 let closeTests state =
   // Note: clear diagnostics also implies clear caches (-> remove file & project options from State).

test/FsAutoComplete.Tests.Lsp/TestCases/Tooltips/Script.fsx

@@ -119,3 +119,6 @@ type NoArgDelegate = delegate of unit -> unit
 type SingleArgDelegate = delegate of arg: string -> int
 type MultiArgDelegate = delegate of a: string * b: int -> bool
 type UnannotatedDelegate = delegate of string -> int
+
+// FSI hash directives — hover tooltip for issue #1225
+#nowarn "40"