Add Sys.which and Sys.isexecutable (#552)

README.md

@@ -295,6 +295,8 @@ Currently, the `@compat` macro supports the following syntaxes:
 
 * `Compat.qr` takes `pivot` as a `Val` _instance_ ([#22475]).
 
+* `Compat.Sys.which` and `Compat.Sys.isexecutable` ([#26559], [#27298]).
+
 * `Compat.rmul!` provides a subset of the functionality of `LinearAlgebra.rmul!` for
   use with Julia 0.6 ([#25701], [#25812]).
 
@@ -633,8 +635,10 @@ includes this fix. Find the minimum version from there.
 [#26436]: https://github.com/JuliaLang/julia/issues/26436
 [#26442]: https://github.com/JuliaLang/julia/issues/26442
 [#26486]: https://github.com/JuliaLang/julia/issues/26486
+[#26559]: https://github.com/JuliaLang/julia/issues/26559
 [#26660]: https://github.com/JuliaLang/julia/issues/26660
 [#26670]: https://github.com/JuliaLang/julia/issues/26670
 [#26850]: https://github.com/JuliaLang/julia/issues/26850
 [#27077]: https://github.com/JuliaLang/julia/issues/27077
-[#27258]: https://github.com/JuliaLang/julia/issues/27258
+[#27258]: https://github.com/JuliaLang/julia/issues/27258
+[#27298]: https://github.com/JuliaLang/julia/issues/27298

src/Compat.jl

@@ -442,6 +442,13 @@ end
 # https://github.com/JuliaLang/julia/pull/21746
 const macros_have_sourceloc = VERSION >= v"0.7-" && length(:(@test).args) == 2
 
+# 0.7.0-DEV.3155
+@static if !isdefined(Base, :pushfirst!)
+    const pushfirst! = unshift!
+    const popfirst! = shift!
+    export pushfirst!, popfirst!
+end
+
 # https://github.com/JuliaLang/julia/pull/22182
 module Sys
     const KERNEL = Base.Sys.KERNEL
@@ -455,6 +462,56 @@ module Sys
         import Base.Sys: isapple, isbsd, islinux, isunix, iswindows
     end
 
+    @static if VERSION < v"0.7.0-DEV.5171"
+        using ..Compat: pushfirst!
+
+        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
+            nothing
+        end
+    elseif VERSION < v"0.7.0-alpha.6"
+        import Base.Sys: isexecutable
+
+        which(program::AbstractString) = try
+            Base.Sys.which(program)
+        catch err
+            err isa ErrorException || rethrow(err)
+            nothing
+        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.
@@ -1130,13 +1187,6 @@ else
     import Base: notnothing
 end
 
-# 0.7.0-DEV.3155
-@static if !isdefined(Base, :pushfirst!)
-    const pushfirst! = unshift!
-    const popfirst! = shift!
-    export pushfirst!, popfirst!
-end
-
 # 0.7.0-DEV.3309
 @static if VERSION < v"0.7.0-DEV.3309"
     const IteratorSize = Base.iteratorsize

test/runtests.jl

@@ -1756,4 +1756,14 @@ end
 @test something(Some(2), 1) === 2
 @test something(nothing, Some(1)) === 1
 
+# 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 Compat.Sys.which("reallyseriouslynotathingyoushouldhave") === nothing
+    end
+end
+
 nothing