From 6543a6c0cf7fa55d813dcd39457bb3a190f03b7d Mon Sep 17 00:00:00 2001
From: Alex Arslan <ararslan@comcast.net>
Date: Tue, 22 May 2018 16:59:25 -0700
Subject: [PATCH] Add Sys.which and Sys.isexecutable

---
 README.md        |  3 +++
 src/Compat.jl    | 39 +++++++++++++++++++++++++++++++++++++++
 test/runtests.jl | 10 ++++++++++
 3 files changed, 52 insertions(+)

diff --git a/README.md b/README.md
index 33341cc95..4ca2297b9 100644
--- a/README.md
+++ b/README.md
@@ -295,6 +295,8 @@ Currently, the `@compat` macro supports the following syntaxes:
 
 * `squeeze` with `dims` as keyword argument ([#26660]).
 
+* `Compat.Sys.which` and `Compat.Sys.isexecutable` ([#26559]).
+
 * `Compat.qr` takes `pivot` as a `Val` _instance_ and keyword argument `full` ([#22475], [#24279]).
 
 * `Compat.rmul!` provides a subset of the functionality of `LinearAlgebra.rmul!` for
@@ -630,6 +632,7 @@ includes this fix. Find the minimum version from there.
 [#26369]: https://github.com/JuliaLang/julia/issues/26369
 [#26436]: https://github.com/JuliaLang/julia/issues/26436
 [#26442]: https://github.com/JuliaLang/julia/issues/26442
+[#26559]: https://github.com/JuliaLang/julia/issues/26559
 [#26660]: https://github.com/JuliaLang/julia/issues/26660
 [#26670]: https://github.com/JuliaLang/julia/issues/26670
 [#27077]: https://github.com/JuliaLang/julia/issues/27077
diff --git a/src/Compat.jl b/src/Compat.jl
index 99dea1564..a35c89baf 100644
--- a/src/Compat.jl
+++ b/src/Compat.jl
@@ -461,6 +461,45 @@ module Sys
         import Base.Sys: isapple, isbsd, islinux, isunix, iswindows
     end
 
+    @static if VERSION < v"0.7.0-DEV.5171"
+        function isexecutable(path::AbstractString)
+            if iswindows()
+                isfile(path)
+            else
+                ccall(:access, Cint, (Ptr{UInt8}, Cint), path, 0x01) == 0
+            end
+        end
+
+        function which(program::AbstractString)
+            progs = String[]
+            base = basename(program)
+            if iswindows()
+                isempty(last(splitext(base))) || push!(progs, base)
+                for p = [".exe", ".com"]
+                    push!(progs, base * p)
+                end
+            else
+                push!(progs, base)
+            end
+            dirs = String[]
+            dir = dirname(program)
+            if isempty(dir)
+                pathsep = iswindows() ? ';' : ':'
+                append!(dirs, map(abspath, split(get(ENV, "PATH", ""), pathsep)))
+                iswindows() && pushfirst!(dirs, pwd())
+            else
+                push!(dirs, abspath(dir))
+            end
+            for d in dirs, p in progs
+                path = joinpath(d, p)
+                isexecutable(path) && return realpath(path)
+            end
+            error("$program not found")
+        end
+    else
+        import Base.Sys: which, isexecutable
+    end
+
     # https://github.com/JuliaLang/julia/pull/25102
     # NOTE: This needs to be in an __init__ because JULIA_HOME is not
     # defined when building system images.
diff --git a/test/runtests.jl b/test/runtests.jl
index bf8394b17..629353e36 100644
--- a/test/runtests.jl
+++ b/test/runtests.jl
@@ -1707,4 +1707,14 @@ end
 @test isletter('β')
 @test !isletter('3')
 
+# 0.7.0-DEV.5171
+let sep = Compat.Sys.iswindows() ? ';' : ':'
+    withenv("PATH" => string(Compat.Sys.BINDIR, sep, get(ENV, "PATH", ""))) do
+        jl = joinpath(Compat.Sys.BINDIR, "julia") * (Compat.Sys.iswindows() ? ".exe" : "")
+        @test Compat.Sys.which("julia") == realpath(jl)
+        @test Compat.Sys.isexecutable(jl)
+        @test_throws ErrorException Compat.Sys.which("reallyseriouslynotathingyoushouldhave")
+    end
+end
+
 nothing