allow artifact string macro to take an explicit path to the artifact file (#46755)

* allow artifact string macro to take an explicit path

can be used by JLLs to avoid scour throgh the file system for the Artifacts.toml when it already knows where it is

* address review comments

* Fix `@artifact_str` invocation

We must provide the `platform` argument here before we provide the
`artifacts_toml_path` argument.

* Catch quoted `nothing` values as well

Co-authored-by: Elliot Saba <[email protected]>

Author: KristofferC

stdlib/Artifacts/src/Artifacts.jl

@@ -652,13 +652,18 @@ access a single file/directory within an artifact.  Example:
 !!! compat "Julia 1.6"
     Slash-indexing requires at least Julia 1.6.
 """
-macro artifact_str(name, platform=nothing)
+macro artifact_str(name, platform=nothing, artifacts_toml_path=nothing)
     # Find Artifacts.toml file we're going to load from
     srcfile = string(__source__.file)
     if ((isinteractive() && startswith(srcfile, "REPL[")) || (!isinteractive() && srcfile == "none")) && !isfile(srcfile)
         srcfile = pwd()
     end
-    local artifacts_toml = find_artifacts_toml(srcfile)
+    # Sometimes we know the exact path to the Artifacts.toml file, so we can save some lookups
+    local artifacts_toml = if artifacts_toml_path === nothing || artifacts_toml_path == :(nothing)
+        find_artifacts_toml(srcfile)
+    else
+        eval(artifacts_toml_path)
+    end
     if artifacts_toml === nothing
         error(string(
             "Cannot locate '(Julia)Artifacts.toml' file when attempting to use artifact '",
@@ -688,7 +693,7 @@ macro artifact_str(name, platform=nothing)
 
     # If `name` is a constant, (and we're using the default `Platform`) we can actually load
     # and parse the `Artifacts.toml` file now, saving the work from runtime.
-    if isa(name, AbstractString) && platform === nothing
+    if isa(name, AbstractString) && (platform === nothing || platform == :(nothing))
         # To support slash-indexing, we need to split the artifact name from the path tail:
         platform = HostPlatform()
         artifact_name, artifact_path_tail, hash = artifact_slash_lookup(name, artifact_dict, artifacts_toml, platform)

stdlib/Artifacts/test/runtests.jl

@@ -91,6 +91,9 @@ end
         HelloWorldC_exe_path = joinpath(HelloWorldC_dir, "bin", "hello_world$(exeext)")
         @test isfile(HelloWorldC_exe_path)
 
+        HelloWorldC_dir_explicit_artifact = eval(:(@artifact_str "HelloWorldC" nothing joinpath(@__DIR__, "Artifacts.toml")))
+        @test isdir(HelloWorldC_dir_explicit_artifact)
+
         # Simple slash-indexed lookup
         HelloWorldC_bin_path = artifact"HelloWorldC/bin"
         @test isdir(HelloWorldC_bin_path)