From e6c789ab80821bd855ef6cff690ed48cf78c0e2f Mon Sep 17 00:00:00 2001
From: "Steven G. Johnson" <stevenj@mit.edu>
Date: Tue, 31 Jul 2018 11:51:49 -0400
Subject: [PATCH] add pathof(::Module) (#28310)

---
 NEWS.md               |  2 ++
 base/exports.jl       |  1 +
 base/loading.jl       | 12 ++++++++++++
 doc/src/base/base.md  |  1 +
 stdlib/Pkg/src/API.jl | 10 +++++-----
 test/loading.jl       |  8 ++++++++
 6 files changed, 29 insertions(+), 5 deletions(-)

diff --git a/NEWS.md b/NEWS.md
index 3a753e812ca37..ae8aae50a88d9 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -549,6 +549,8 @@ Library improvements
   * `Char` is now a subtype of `AbstractChar`, and most of the functions that
     take character arguments now accept any `AbstractChar` ([#26286]).
 
+  * `pathof(module)` returns the path a module was imported from ([#28310]).
+
   * `bytes2hex` now accepts an optional `io` argument to output to a hexadecimal stream
     without allocating a `String` first ([#27121]).
 
diff --git a/base/exports.jl b/base/exports.jl
index 73e11eb65ddec..d979ec2080be2 100644
--- a/base/exports.jl
+++ b/base/exports.jl
@@ -739,6 +739,7 @@ export
     methods,
     nameof,
     parentmodule,
+    pathof,
     names,
     which,
     @isdefined,
diff --git a/base/loading.jl b/base/loading.jl
index 1bca9ee0b1049..00c6c4e02fbae 100644
--- a/base/loading.jl
+++ b/base/loading.jl
@@ -249,6 +249,18 @@ function locate_package(pkg::PkgId)::Union{Nothing,String}
 end
 locate_package(::Nothing) = nothing
 
+"""
+    pathof(m::Module)
+
+Return the path of `m.jl` file that was used to `import` module `m`,
+or `nothing` if `m` was not imported from a package.
+"""
+function pathof(m::Module)
+    pkgid = get(Base.module_keys, m, nothing)
+    pkgid === nothing && return nothing
+    return Base.locate_package(pkgid)
+end
+
 ## generic project & manifest API ##
 
 const project_names = ("JuliaProject.toml", "Project.toml")
diff --git a/doc/src/base/base.md b/doc/src/base/base.md
index d2a6dd168c875..33554927d5a4a 100644
--- a/doc/src/base/base.md
+++ b/doc/src/base/base.md
@@ -332,6 +332,7 @@ Base.AsyncCondition(::Function)
 ```@docs
 Base.nameof(::Module)
 Base.parentmodule
+Base.pathof(::Module)
 Base.moduleroot
 Base.@__MODULE__
 Base.fullname
diff --git a/stdlib/Pkg/src/API.jl b/stdlib/Pkg/src/API.jl
index af6e35729cb52..afdc7e9c4e2bc 100644
--- a/stdlib/Pkg/src/API.jl
+++ b/stdlib/Pkg/src/API.jl
@@ -432,13 +432,13 @@ function clone(url::String, name::String = "")
     develop(ctx, [Pkg.REPLMode.parse_package(url; add_or_develop=true)])
 end
 
-function dir(pkg::String, paths::String...)
-    @warn "Pkg.dir is only kept for legacy CI script reasons" maxlog=1
+function dir(pkg::String, paths::AbstractString...)
+    @warn "`Pkg.dir(pkgname, paths...)` is deprecated; instead, do `import $pkg; joinpath(dirname(pathof($pkg)), \"..\", paths...)`." maxlog=1
     pkgid = Base.identify_package(pkg)
-    pkgid == nothing && return nothing
+    pkgid === nothing && return nothing
     path = Base.locate_package(pkgid)
-    pkgid == nothing && return nothing
-    return joinpath(abspath(path, "..", "..", paths...))
+    path === nothing && return nothing
+    return abspath(path, "..", "..", paths...)
 end
 
 precompile() = precompile(Context())
diff --git a/test/loading.jl b/test/loading.jl
index 0517511d66e18..289c25e582b0a 100644
--- a/test/loading.jl
+++ b/test/loading.jl
@@ -218,6 +218,8 @@ Base.ACTIVE_PROJECT[] = nothing
     end
 end
 
+module NotPkgModule; end
+
 @testset "project & manifest import" begin
     @test !@isdefined Foo
     @test !@isdefined Bar
@@ -254,6 +256,12 @@ end
         end
     end
     @test Foo.which == "path"
+
+    @testset "pathof" begin
+        @test pathof(Foo) == normpath(abspath(@__DIR__, "project/deps/Foo1/src/Foo.jl"))
+        @test pathof(NotPkgModule) === nothing
+    end
+
 end
 
 ## systematic generation of test environments ##