Resolve custom steps from external assemblies (#976)

* Resolve custom steps from external assemblies

* Preserve order of custom steps.
Add `--custom-assembly` command line option.
Updater src\linker readme.

* Remove GetCustomStepParams.

* Address fedback

* Remove --custom-assembly option

* Address Marek's feedback

* Fix the usage message to use single comma for assembly path separator

* Use single comma for assembly path separator

* Update test/Mono.Linker.Tests.Cases/CommandLine/AddCustomStep.cs

Co-Authored-By: Marek Safar <marek.safar@gmail.com>

Co-authored-by: Vitek Karas <vitek.karas@microsoft.com>
Co-authored-by: Marek Safar <marek.safar@gmail.com>

1 files changed, 10 insertions, 0 deletions

diff --git a/test/Mono.Linker.Tests/TestCasesRunner/TestCaseMetadaProvider.cs b/test/Mono.Linker.Tests/TestCasesRunner/TestCaseMetadaProvider.cs
index cb0d855c8..32244f654 100644
--- a/test/Mono.Linker.Tests/TestCasesRunner/TestCaseMetadaProvider.cs
+++ b/test/Mono.Linker.Tests/TestCasesRunner/TestCaseMetadaProvider.cs
@@ -55,6 +55,16 @@ namespace Mono.Linker.Tests.TestCasesRunner {
 			{
 				var ca = additionalArgumentAttr.ConstructorArguments;
 				var values = ((CustomAttributeArgument [])ca [1].Value)?.Select (arg => arg.Value.ToString ()).ToArray ();
+				// Since custom attribute arguments need to be constant expressions, we need to add
+				// the path to the temp directory (where the custom assembly is located) here.
+				if ((string)ca [0].Value == "--custom-step") {
+					int pos = values [0].IndexOf (",");
+					if (pos != -1) {
+						string custom_assembly_path = values [0].Substring (pos + 1);
+						if (!Path.IsPathRooted (custom_assembly_path))
+							values [0] = values [0].Substring (0, pos + 1) + Path.Combine (inputPath, custom_assembly_path);
+					}
+				}
 				tclo.AdditionalArguments.Add (new KeyValuePair<string, string []> ((string)ca [0].Value, values));
 			}