Make tree hash mismatch fatal again and use

    JULIA_PKG_IGNORE_HASHES=1
to manually ignore them, fixes #2317.

src/Artifacts.jl

@@ -349,10 +349,22 @@ function download_artifact(
             msg  = "Tree Hash Mismatch!\n"
             msg *= "  Expected git-tree-sha1:   $(bytes2hex(tree_hash.bytes))\n"
             msg *= "  Calculated git-tree-sha1: $(bytes2hex(calc_hash.bytes))"
+            # Since tree hash calculation is still broken on some systems, e.g. Pkg.jl#1860,
+            # and Pkg.jl#2317 so we allow setting JULIA_PKG_IGNORE_HASHES=1 to ignore the
+            # error and move the artifact to the expected location and return true
+            ignore_hash = get(ENV, "JULIA_PKG_IGNORE_HASHES", nothing) == "1"
+            if ignore_hash
+                msg *= "\n\$JULIA_PKG_IGNORE_HASHES is set to 1: ignoring error and moving artifact to the expected location"
+            end
             @error(msg)
-            # Tree hash calculation is still broken on some systems, e.g. Pkg.jl#1860,
-            # so we return true here and only raise the warning on the lines above.
-            # return false
+            if ignore_hash
+                # Move it to the location we expected
+                src = artifact_path(calc_hash; honor_overrides=false)
+                dst = artifact_path(tree_hash; honor_overrides=false)
+                mv(src, dst; force=true)
+                return true
+            end
+            return false
         end
     end
 

test/artifacts.jl

@@ -268,17 +268,20 @@ end
 
     # Next, test incorrect download errors
     if !Sys.iswindows()
-        mktempdir() do dir
+        for ignore_hash in (false, true); withenv("JULIA_PKG_IGNORE_HASHES" => ignore_hash ? "1" : nothing) do; mktempdir() do dir
             with_artifacts_directory(dir) do
                 @test artifact_meta("broken_artifact", joinpath(badifact_dir, "incorrect_gitsha.toml")) != nothing
                 @test_logs (:error, r"Tree Hash Mismatch!") match_mode=:any begin
-                    # Only warn on wrong tree hash for now (see Pkg.jl#1885)
-                    # @test_throws ErrorException ensure_artifact_installed("broken_artifact", joinpath(badifact_dir, "incorrect_gitsha.toml"))
-                    path = ensure_artifact_installed("broken_artifact", joinpath(badifact_dir, "incorrect_gitsha.toml"))
-                    @test endswith(path, "0000000000000000000000000000000000000000")
+                    if !ignore_hash
+                        @test_throws ErrorException ensure_artifact_installed("broken_artifact", joinpath(badifact_dir, "incorrect_gitsha.toml"))
+                    else
+                        path = ensure_artifact_installed("broken_artifact", joinpath(badifact_dir, "incorrect_gitsha.toml"))
+                        @test endswith(path, "0000000000000000000000000000000000000000")
+                        @test isdir(path)
+                    end
                 end
             end
-        end
+        end end end
     end
 
     mktempdir() do dir