BuildCommandAutoRule: expose more information

We expose the list of candidate script paths and the chosen script path
so that we can inspect them for diagnostics purposes.

csharp/autobuilder/Semmle.Autobuild.Shared/BuildCommandAutoRule.cs

@@ -10,23 +10,51 @@ namespace Semmle.Autobuild.Shared
     public class BuildCommandAutoRule : IBuildRule<AutobuildOptionsShared>
     {
         private readonly WithDotNet<AutobuildOptionsShared> withDotNet;
+        private IEnumerable<string> candidatePaths;
+        private string? scriptPath;
+
+        /// <summary>
+        /// A list of paths to files in the project directory which we classified as scripts.
+        /// </summary>
+        public IEnumerable<string> CandidatePaths
+        {
+            get { return this.candidatePaths; }
+        }
+
+        /// <summary>
+        /// The path of the script we decided to run, if any.
+        /// </summary>
+        public string? ScriptPath
+        {
+            get { return this.scriptPath; }
+        }
 
         public BuildCommandAutoRule(WithDotNet<AutobuildOptionsShared> withDotNet)
         {
             this.withDotNet = withDotNet;
+            this.candidatePaths = new List<string>();
         }
 
+        /// <summary>
+        /// A list of extensions that we consider to be for scripts on Windows.
+        /// </summary>
         private readonly IEnumerable<string> winExtensions = new List<string> {
             ".bat",
             ".cmd",
             ".exe"
         };
 
+        /// <summary>
+        /// A list of extensions that we consider to be for scripts on Linux.
+        /// </summary>
         private readonly IEnumerable<string> linuxExtensions = new List<string> {
             "",
             ".sh"
         };
 
+        /// <summary>
+        /// A list of filenames without extensions that we think might be build scripts.
+        /// </summary>
         private readonly IEnumerable<string> buildScripts = new List<string> {
             "build"
         };
@@ -35,9 +63,16 @@ namespace Semmle.Autobuild.Shared
         {
             builder.Log(Severity.Info, "Attempting to locate build script");
 
+            // a list of extensions for files that we consider to be scripts on the current platform
             var extensions = builder.Actions.IsWindows() ? winExtensions : linuxExtensions;
+            // a list of combined base script names with the current platform's script extensions
+            // e.g. for Linux: build, build.sh
             var scripts = buildScripts.SelectMany(s => extensions.Select(e => s + e));
-            var scriptPath = builder.Paths.Where(p => scripts.Any(p.Item1.ToLower().EndsWith)).OrderBy(p => p.Item2).Select(p => p.Item1).FirstOrDefault();
+            // search through the files in the project directory for paths which end in one of
+            // the names given by `scripts`, then order them by their distance from the root
+            this.candidatePaths = builder.Paths.Where(p => scripts.Any(p.Item1.ToLower().EndsWith)).OrderBy(p => p.Item2).Select(p => p.Item1);
+            // pick the first matching path, if there is one
+            this.scriptPath = candidatePaths.FirstOrDefault();
 
             if (scriptPath is null)
                 return BuildScript.Failure;