fsharp-diagnostics - SKILL.md Agent Skill

name: fsharp-diagnostics description: Always invoke after editing `.fs` files under `src/Compiler/`. Fast parse/typecheck without `dotnet build`, plus symbol references and inferred type hints. Use whenever the user asks about F# errors, compile errors, type inference, finding usages, or renaming a symbol in the compiler tree.

F# Diagnostics

Scope: src/Compiler/ files only.

Setup (once per session)

Requires pwsh 7+ (brew install powershell / winget install Microsoft.PowerShell / apt install powershell).

function GetErrors { & "$(git rev-parse --show-toplevel)/.github/skills/fsharp-diagnostics/scripts/get-fsharp-errors.ps1" @args }

From bash/zsh without a function: pwsh -File <repo>/.github/skills/fsharp-diagnostics/scripts/get-fsharp-errors.ps1 <args>.

Parse first, typecheck second

GetErrors -ParseOnly src/Compiler/Checking/CheckBasics.fs   # syntax only
GetErrors            src/Compiler/Checking/CheckBasics.fs   # full typecheck

Fix all parse errors before typechecking; type errors on top of bad syntax are noise.

Symbol references (line 1-based, col 0-based)

GetErrors -FindRefs src/Compiler/Checking/CheckBasics.fs 30 5

Use before any rename.

Type hints (line range, 1-based)

Returns the range with inferred types as inline // (name: Type) comments:

GetErrors -TypeHints src/Compiler/TypedTree/TypedTreeOps.Transforms.fs 100 120

Other

GetErrors -CheckProject   # typecheck entire project
GetErrors -Ping           # liveness check, no side effects
GetErrors -Shutdown

Timing

First real call after a fresh clone: server build + in-memory warmup, 5–15 min → initial_wait=1200.
After warmup: real commands answer in seconds → initial_wait=180.
-Ping / -Shutdown: sub-second; never trigger build or warmup.

Auto-shuts down after 4h idle; ~3 GB RAM while running.