F# inline MSBuild tasks via FSharp.Compiler.CodeDom

FindExecutable.fs

namespace Example

open System
open System.IO
open System.Runtime.InteropServices
open System.Text
open Microsoft.Build.Framework
open Microsoft.Build.Utilities

module internal Externs =
  [<DllImport("shlwapi.dll",
              EntryPoint = "AssocQueryString",
              CharSet = CharSet.Auto)>]
  extern int AssocQueryString(int flags,
                              int str,
                              string pszAssoc,
                              string pszExtra,
                              [<Out>] StringBuilder pszOut,
                              [<In; Out>] int& pcchOut)

type FindExecutable() =
  inherit Task()

  [<Literal>]
  static let ASSOCF_INIT_BYEXENAME = 0x00000002
  [<Literal>]
  static let ASSOCF_NOTRUNCATE = 0x00000020
  [<Literal>]
  static let ASSOCSTR_EXECUTABLE = 2
  static let windir =
    System.Environment.GetFolderPath(System.Environment.SpecialFolder.Windows)
  static let sysdir = System.Environment.SystemDirectory

  static let find_in_paths name paths =
    let f p =
      let full_path = Path.Combine(p, name)
      File.Exists(full_path)
    match Array.tryFind f paths with
    | None -> failwith "file not found"
    | Some x -> x

  static let find_executable name paths =
    if File.Exists(name) then Path.GetFullPath(name) else
    let path = Path.Combine(windir, name)
    if File.Exists(path) then Path.GetFullPath(path) else
    let path = Path.Combine(sysdir, name)
    if File.Exists(path) then Path.GetFullPath(path) else
    let res =
      try
        let envpaths =
          let ep = System.Environment.GetEnvironmentVariable("PATH")
          if ep <> null then ep else ""
        if String.Empty <> envpaths
        then find_in_paths name (envpaths.Split(';'))
        else ""
      with
      | _ -> ""
    if String.Empty <> res then res else
    let extrapaths = if paths <> null
                     then paths
                     else [| TaskItem() :> ITaskItem |]
    if 0 <> extrapaths.Length then
      let strpaths = extrapaths |> Array.map (fun l -> l.ItemSpec)
      find_in_paths name strpaths
    else failwith "file not found"

  let mutable _name : string = null
  let mutable _additional_paths : ITaskItem [] = null
  let mutable _location : string = null

  [<Required>]
  member x.Name with get() = _name and set v = _name <- v

  member x.AdditionalPaths with get () = _additional_paths
                           and set v = _additional_paths <- v

  [<Output>]
  member x.Location with get () = _location and private set v = _location <- v

  override this.Execute() =
    let res =
      try
        this.Location <- find_executable this.Name this.AdditionalPaths
        Some true
      with
      | _ -> None
    match res with
    | Some x -> x
    | None ->
        let mutable sz = 0
        let hr =
          Externs.AssocQueryString(
            ASSOCF_INIT_BYEXENAME ||| ASSOCF_NOTRUNCATE,
            ASSOCSTR_EXECUTABLE,
            this.Name,
            null,
            null,
            &sz)
        if 0 > hr then
          this.Location <- ""
          false
        else
        let sb = StringBuilder(sz + 1)
        Externs.AssocQueryString(
          ASSOCF_INIT_BYEXENAME ||| ASSOCF_NOTRUNCATE,
          ASSOCSTR_EXECUTABLE,
          this.Name,
          null,
          sb,
          &sz) |> ignore
        this.Location <- sb.ToString()
        true

output.txt

C:\Users\msjp_000\Documents\Visual Studio 2013\Projects\tmp>msbuild Test.proj
Microsoft (R) Build Engine version 12.0.31101.0
[Microsoft .NET Framework, version 4.0.30319.34209]
Copyright (C) Microsoft Corporation. All rights reserved.

Build started 2015/04/21 1:49:09.
Project "C:\Users\msjp_000\Documents\Visual Studio 2013\Projects\tmp\Test.proj" on node 1 (default targets).
Build:
  C:\Windows\notepad.exe
Done Building Project "C:\Users\msjp_000\Documents\Visual Studio 2013\Projects\tmp\Test.proj" (default targets) .


Build succeeded.
    0 Warning(s)
    0 Error(s)

Time Elapsed 00:00:00.68

Test.proj

<?xml version="1.0" encoding="utf-8"?>
<Project ToolsVersion="12.0" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
  <UsingTask TaskName="Example.FindExecutable"
             TaskFactory="CodeTaskFactory"
             AssemblyFile="$(MSBuildToolsPath)\Microsoft.Build.Tasks.v12.0.dll">
    <ParameterGroup>
      <Name ParameterType="System.String" Required="true" />
      <AdditionalPaths ParameterType="Microsoft.Build.Framework.ITaskItem[]" />
      <Location ParameterType="System.String" Output="true" />
    </ParameterGroup>
    <Task>
      <Code Type="Class" Language="f#" Source="$(MSBuildThisFileDirectory)FindExecutable.fs" />
    </Task>
  </UsingTask>
  <Target Name="Build">
    <Example.FindExecutable Name="notepad.exe" ContinueOnError="WarnAndContinue">
      <Output PropertyName="NotepadPath" TaskParameter="Location" />
    </Example.FindExecutable>
    <Message Text="$(NotepadPath)" Importance="High" />
  </Target>
</Project>