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.md skill added to get fsharp-diagnostics (like IDE does, via FsharpChecker) (#19263)
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‎.github/skills/fsharp-diagnostics/SKILL.md‎

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---
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name: fsharp-diagnostics
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description: "After modifying any F# file, use this to get quick parse errors and typecheck warnings+errors. Also finds symbol references and inferred type hints."
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---
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# F# Diagnostics
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**Scope:** `src/Compiler/` files only (`FSharp.Compiler.Service.fsproj`, Release, net10.0).
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## Setup (run once per shell session)
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```bash
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GetErrors() { "$(git rev-parse --show-toplevel)/.github/skills/fsharp-diagnostics/scripts/get-fsharp-errors.sh" "$@"; }
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```
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## Parse first, typecheck second
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```bash
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GetErrors --parse-only src/Compiler/Checking/CheckBasics.fs
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```
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If errors → fix syntax. Do NOT typecheck until parse is clean.
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```bash
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GetErrors src/Compiler/Checking/CheckBasics.fs
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```
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## Find references for a single symbol (line 1-based, col 0-based)
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Before renaming or to understand call sites:
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```bash
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GetErrors --find-refs src/Compiler/Checking/CheckBasics.fs 30 5
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```
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## Type hints for a range selection (begin and end line numbers, 1-based)
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To see inferred types as inline `// (name: Type)` comments:
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```bash
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GetErrors --type-hints src/Compiler/TypedTree/TypedTreeOps.fs 1028 1032
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```
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## Other
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```bash
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GetErrors --check-project # typecheck entire project
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GetErrors --ping
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GetErrors --shutdown
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```
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First call starts server (~70s cold start, set initial_wait=600). Auto-shuts down after 4h idle. ~3 GB RAM.

‎.github/skills/fsharp-diagnostics/scripts/get-fsharp-errors.sh‎

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#!/usr/bin/env bash
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set -euo pipefail
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# get-fsharp-errors.sh — minimal passthrough client for fsharp-diag-server
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# Usage:
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# get-fsharp-errors.sh [--parse-only] <file.fs>
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# get-fsharp-errors.sh --check-project <project.fsproj>
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# get-fsharp-errors.sh --ping
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# get-fsharp-errors.sh --shutdown
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SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd)"
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SERVER_PROJECT="$(cd "$SCRIPT_DIR/../server" && pwd)"
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SOCK_DIR="$HOME/.fsharp-diag"
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get_repo_root() {
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git rev-parse --show-toplevel 2>/dev/null || pwd
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}
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get_socket_path() {
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local root="$1"
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local hash
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hash=$(printf '%s' "$root" | shasum -a 256 | cut -c1-16)
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echo "$SOCK_DIR/${hash}.sock"
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}
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ensure_server() {
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local root="$1"
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local sock="$2"
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# Check if socket exists and server responds to ping
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if [ -S "$sock" ]; then
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local pong
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pong=$(printf '{"command":"ping"}\n' | nc -U "$sock" 2>/dev/null || true)
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if echo "$pong" | grep -q '"ok"'; then
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return 0
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fi
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# Stale socket
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rm -f "$sock"
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fi
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# Start server
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mkdir -p "$SOCK_DIR"
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local log_hash
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log_hash=$(printf '%s' "$root" | shasum -a 256 | cut -c1-16)
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local log_file="$SOCK_DIR/${log_hash}.log"
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nohup dotnet run -c Release --project "$SERVER_PROJECT" -- --repo-root "$root" > "$log_file" 2>&1 &
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# Wait for socket to appear (max 60s)
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local waited=0
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while [ ! -S "$sock" ] && [ $waited -lt 60 ]; do
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sleep 1
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waited=$((waited + 1))
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done
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if [ ! -S "$sock" ]; then
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echo '{"error":"Server failed to start within 60s. Check log: '"$log_file"'"}' >&2
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exit 1
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fi
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}
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send_request() {
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local sock="$1"
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local request="$2"
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printf '%s\n' "$request" | nc -U "$sock"
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}
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# --- Main ---
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REPO_ROOT=$(get_repo_root)
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SOCK_PATH=$(get_socket_path "$REPO_ROOT")
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case "${1:-}" in
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--ping)
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ensure_server "$REPO_ROOT" "$SOCK_PATH"
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send_request "$SOCK_PATH" '{"command":"ping"}'
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;;
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--shutdown)
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send_request "$SOCK_PATH" '{"command":"shutdown"}'
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;;
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--parse-only)
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shift
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FILE=$(cd "$(dirname "$1")" && pwd)/$(basename "$1")
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ensure_server "$REPO_ROOT" "$SOCK_PATH"
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send_request "$SOCK_PATH" "{\"command\":\"parseOnly\",\"file\":\"$FILE\"}"
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;;
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--check-project)
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ensure_server "$REPO_ROOT" "$SOCK_PATH"
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send_request "$SOCK_PATH" '{"command":"checkProject"}'
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;;
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--find-refs)
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shift
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FILE=$(cd "$(dirname "$1")" && pwd)/$(basename "$1")
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LINE="$2"
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COL="$3"
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ensure_server "$REPO_ROOT" "$SOCK_PATH"
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send_request "$SOCK_PATH" "{\"command\":\"findRefs\",\"file\":\"$FILE\",\"line\":$LINE,\"col\":$COL}"
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;;
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--type-hints)
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shift
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FILE=$(cd "$(dirname "$1")" && pwd)/$(basename "$1")
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START_LINE="$2"
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END_LINE="$3"
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ensure_server "$REPO_ROOT" "$SOCK_PATH"
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send_request "$SOCK_PATH" "{\"command\":\"typeHints\",\"file\":\"$FILE\",\"startLine\":$START_LINE,\"endLine\":$END_LINE}"
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;;
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-*)
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echo "Usage: get-fsharp-errors [--parse-only] <file.fs>" >&2
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echo " get-fsharp-errors --check-project <project.fsproj>" >&2
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echo " get-fsharp-errors --ping | --shutdown" >&2
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exit 1
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;;
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*)
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FILE=$(cd "$(dirname "$1")" && pwd)/$(basename "$1")
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ensure_server "$REPO_ROOT" "$SOCK_PATH"
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send_request "$SOCK_PATH" "{\"command\":\"check\",\"file\":\"$FILE\"}"
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;;
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esac

‎.github/skills/fsharp-diagnostics/server/DesignTimeBuild.fs‎

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module FSharpDiagServer.DesignTimeBuild
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open System
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open System.Diagnostics
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open System.IO
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open System.Text.Json
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type DtbResult =
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{ CompilerArgs: string array }
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type DtbConfig =
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{ TargetFramework: string option
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Configuration: string }
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let defaultConfig =
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{ TargetFramework = Some "net10.0"
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Configuration = "Release" }
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let run (fsprojPath: string) (config: DtbConfig) =
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async {
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let tfmArg =
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config.TargetFramework
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|> Option.map (fun tfm -> $" /p:TargetFramework={tfm}")
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|> Option.defaultValue ""
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let projDir = Path.GetDirectoryName(fsprojPath)
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// /t:Build runs BeforeBuild (generates buildproperties.fs via CompileBefore).
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// DesignTimeBuild=true skips dependency projects.
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// SkipCompilerExecution=true + ProvideCommandLineArgs=true populates FscCommandLineArgs without compiling.
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let psi =
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ProcessStartInfo(
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FileName = "dotnet",
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Arguments =
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$"msbuild \"{fsprojPath}\" /t:Build /p:DesignTimeBuild=true /p:SkipCompilerExecution=true /p:ProvideCommandLineArgs=true /p:CopyBuildOutputToOutputDirectory=false /p:CopyOutputSymbolsToOutputDirectory=false /p:BUILDING_USING_DOTNET=true /p:Configuration={config.Configuration}{tfmArg} /nologo /v:q /getItem:FscCommandLineArgs",
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RedirectStandardOutput = true,
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RedirectStandardError = true,
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UseShellExecute = false,
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WorkingDirectory = projDir
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)
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use proc = Process.Start(psi)
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let! stdout = proc.StandardOutput.ReadToEndAsync() |> Async.AwaitTask
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let! stderr = proc.StandardError.ReadToEndAsync() |> Async.AwaitTask
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do! proc.WaitForExitAsync() |> Async.AwaitTask
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if proc.ExitCode <> 0 then
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return Error $"DTB failed (exit {proc.ExitCode}): {stderr}"
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else
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try
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// MSBuild may emit warnings before the JSON; find the JSON start
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let jsonStart = stdout.IndexOf('{')
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if jsonStart < 0 then
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return Error $"No JSON in DTB output: {stdout.[..200]}"
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else
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let doc = JsonDocument.Parse(stdout.Substring(jsonStart))
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let items = doc.RootElement.GetProperty("Items")
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let args =
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items.GetProperty("FscCommandLineArgs").EnumerateArray()
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|> Seq.map (fun e -> e.GetProperty("Identity").GetString())
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|> Seq.toArray
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return Ok { CompilerArgs = args }
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with ex ->
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return Error $"Failed to parse DTB output: {ex.Message}"
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}

‎.github/skills/fsharp-diagnostics/server/DiagnosticsFormatter.fs‎

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module FSharpDiagServer.DiagnosticsFormatter
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open FSharp.Compiler.Diagnostics
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let private formatOne (getLines: string -> string[]) (d: FSharpDiagnostic) =
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let sev = match d.Severity with FSharpDiagnosticSeverity.Error -> "ERROR" | _ -> "WARNING"
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let lines = getLines d.Range.FileName
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let src = if d.StartLine >= 1 && d.StartLine <= lines.Length then $" | {lines.[d.StartLine - 1].Trim()}" else ""
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$"{sev} {d.ErrorNumberText} ({d.StartLine},{d.Start.Column}-{d.EndLine},{d.End.Column}) {d.Message.Replace('\n', ' ').Replace('\r', ' ')}{src}"
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let private withLineReader f =
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let cache = System.Collections.Generic.Dictionary<string, string[]>()
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let getLines path =
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match cache.TryGetValue(path) with
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| true, l -> l
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| _ -> let l = try System.IO.File.ReadAllLines(path) with _ -> [||] in cache.[path] <- l; l
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f getLines
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let private relevant (diags: FSharpDiagnostic array) =
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diags |> Array.filter (fun d -> d.Severity = FSharpDiagnosticSeverity.Error || d.Severity = FSharpDiagnosticSeverity.Warning)
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let formatFile (diags: FSharpDiagnostic array) =
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let diags = relevant diags
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if diags.Length = 0 then "OK"
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else withLineReader (fun getLines -> diags |> Array.map (formatOne getLines) |> String.concat "\n")
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let formatProject (repoRoot: string) (diags: FSharpDiagnostic array) =
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let diags = relevant diags
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if diags.Length = 0 then "OK"
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else
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let root = repoRoot.TrimEnd('/') + "/"
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let rel (path: string) = if path.StartsWith(root) then path.Substring(root.Length) else path
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withLineReader (fun getLines ->
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diags
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|> Array.groupBy (fun d -> d.Range.FileName)
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|> Array.collect (fun (f, ds) -> Array.append [| $"--- {rel f}" |] (ds |> Array.map (formatOne getLines)))
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|> String.concat "\n")

‎.github/skills/fsharp-diagnostics/server/Directory.Build.props‎

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<Project>
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<!-- Stops repo-level Directory.Build.props traversal (this file is the first found).
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Also blocks Directory.Build.targets import. -->
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<PropertyGroup>
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<ImportDirectoryBuildTargets>false</ImportDirectoryBuildTargets>
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<BaseOutputPath>$(MSBuildThisFileDirectory)../../../../.tools/fsharp-diag/bin/</BaseOutputPath>
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<BaseIntermediateOutputPath>$(MSBuildThisFileDirectory)../../../../.tools/fsharp-diag/obj/</BaseIntermediateOutputPath>
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</PropertyGroup>
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</Project>

‎.github/skills/fsharp-diagnostics/server/FSharpDiagServer.fsproj‎

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<Project Sdk="Microsoft.NET.Sdk">
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<PropertyGroup>
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<OutputType>Exe</OutputType>
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<TargetFramework>net10.0</TargetFramework>
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</PropertyGroup>
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<ItemGroup>
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<PackageReference Include="FSharp.Compiler.Service" Version="43.*" />
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<PackageReference Update="FSharp.Core" Version="10.*" />
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</ItemGroup>
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<ItemGroup>
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<Compile Include="DesignTimeBuild.fs" />
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<Compile Include="ProjectManager.fs" />
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<Compile Include="DiagnosticsFormatter.fs" />
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<Compile Include="Server.fs" />
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<Compile Include="Program.fs" />
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</ItemGroup>
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</Project>

‎.github/skills/fsharp-diagnostics/server/Program.fs‎

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module FSharpDiagServer.Program
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open System
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[<EntryPoint>]
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let main argv =
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let mutable repoRoot = Environment.CurrentDirectory
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let mutable i = 0
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while i < argv.Length do
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match argv.[i] with
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| "--repo-root" when i + 1 < argv.Length ->
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repoRoot <- argv.[i + 1]
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i <- i + 2
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| other ->
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eprintfn $"Unknown argument: {other}"
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i <- i + 1
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// Resolve to absolute path
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repoRoot <- IO.Path.GetFullPath(repoRoot)
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let config: Server.ServerConfig =
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{ RepoRoot = repoRoot
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IdleTimeoutMinutes = 240.0 }
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eprintfn $"[fsharp-diag] Starting server for {repoRoot}"
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eprintfn $"[fsharp-diag] Socket: {Server.deriveSocketPath repoRoot}"
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Server.startServer config |> Async.RunSynchronously
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0

‎.github/skills/fsharp-diagnostics/server/ProjectManager.fs‎

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module FSharpDiagServer.ProjectManager
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open System.IO
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open FSharp.Compiler.CodeAnalysis
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type ProjectManager(checker: FSharpChecker) =
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let mutable cached: (System.DateTime * FSharpProjectOptions) option = None
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let gate = obj ()
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let isSourceFile (s: string) =
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not (s.StartsWith("-"))
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&& (s.EndsWith(".fs", System.StringComparison.OrdinalIgnoreCase)
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|| s.EndsWith(".fsi", System.StringComparison.OrdinalIgnoreCase))
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member _.ResolveProjectOptions(fsprojPath: string) =
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async {
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let fsprojMtime = File.GetLastWriteTimeUtc(fsprojPath)
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let current =
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lock gate (fun () ->
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match cached with
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| Some(mtime, opts) when mtime = fsprojMtime -> Some opts
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| Some _ -> cached <- None; None
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| None -> None)
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match current with
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| Some opts -> return Ok opts
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| None ->
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let! dtbResult = DesignTimeBuild.run fsprojPath DesignTimeBuild.defaultConfig
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match dtbResult with
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| Error msg -> return Error msg
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| Ok dtb ->
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let projDir = Path.GetDirectoryName(fsprojPath)
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let resolve (s: string) =
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if Path.IsPathRooted(s) then s else Path.GetFullPath(Path.Combine(projDir, s))
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let resolvedArgs =
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dtb.CompilerArgs
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|> Array.map (fun a -> if isSourceFile a then resolve a else a)
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let sourceFiles = resolvedArgs |> Array.filter isSourceFile
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let flagsOnly = resolvedArgs |> Array.filter (not << isSourceFile)
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let opts = checker.GetProjectOptionsFromCommandLineArgs(fsprojPath, flagsOnly)
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let options = { opts with SourceFiles = sourceFiles }
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lock gate (fun () -> cached <- Some(fsprojMtime, options))
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return Ok options
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}
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member _.Invalidate() = lock gate (fun () -> cached <- None)

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