Revert "remove variable and build arg paths"

This reverts commit 793e54d.

src/Microsoft.ComponentDetection.Common/ComponentDetectionConfigFileService.cs

@@ -10,19 +10,23 @@ namespace Microsoft.ComponentDetection.Common;
 /// <inheritdoc />
 public class ComponentDetectionConfigFileService : IComponentDetectionConfigFileService
 {
+    private const string ComponentDetectionConfigFileEnvVar = "ComponentDetection.ComponentDetectionConfigFile";
     private readonly IFileUtilityService fileUtilityService;
+    private readonly IEnvironmentVariableService environmentVariableService;
     private readonly IPathUtilityService pathUtilityService;
     private readonly ComponentDetectionConfigFile componentDetectionConfig;
     private readonly ILogger<FastDirectoryWalkerFactory> logger;
     private bool serviceInitComplete;
 
     public ComponentDetectionConfigFileService(
         IFileUtilityService fileUtilityService,
+        IEnvironmentVariableService environmentVariableService,
         IPathUtilityService pathUtilityService,
         ILogger<FastDirectoryWalkerFactory> logger)
     {
         this.fileUtilityService = fileUtilityService;
         this.pathUtilityService = pathUtilityService;
+        this.environmentVariableService = environmentVariableService;
         this.logger = logger;
         this.componentDetectionConfig = new ComponentDetectionConfigFile();
         this.serviceInitComplete = false;
@@ -36,6 +40,12 @@ public ComponentDetectionConfigFile GetComponentDetectionConfig()
 
     public async Task InitAsync(string explicitConfigPath, string rootDirectoryPath = null)
     {
+        await this.LoadFromEnvironmentVariableAsync();
+        if (!string.IsNullOrEmpty(explicitConfigPath))
+        {
+            await this.LoadComponentDetectionConfigAsync(explicitConfigPath);
+        }
+
         if (!string.IsNullOrEmpty(rootDirectoryPath))
         {
             await this.LoadComponentDetectionConfigFilesFromRootDirectoryAsync(rootDirectoryPath);
@@ -55,6 +65,18 @@ private async Task LoadComponentDetectionConfigFilesFromRootDirectoryAsync(strin
         }
     }
 
+    private async Task LoadFromEnvironmentVariableAsync()
+    {
+        if (this.environmentVariableService.DoesEnvironmentVariableExist(ComponentDetectionConfigFileEnvVar))
+        {
+            var possibleConfigFilePath = this.environmentVariableService.GetEnvironmentVariable(ComponentDetectionConfigFileEnvVar);
+            if (this.fileUtilityService.Exists(possibleConfigFilePath))
+            {
+                await this.LoadComponentDetectionConfigAsync(possibleConfigFilePath);
+            }
+        }
+    }
+
     private async Task LoadComponentDetectionConfigAsync(string configFile)
     {
         if (!this.fileUtilityService.Exists(configFile))
@@ -65,9 +87,25 @@ private async Task LoadComponentDetectionConfigAsync(string configFile)
         var configFileInfo = new FileInfo(configFile);
         var fileContents = await this.fileUtilityService.ReadAllTextAsync(configFileInfo);
         var newConfig = this.ParseComponentDetectionConfig(fileContents);
+        this.MergeComponentDetectionConfig(newConfig);
         this.logger.LogInformation("Loaded component detection config file from {ConfigFile}", configFile);
     }
 
+    /// <summary>
+    /// Merges two component detection configs, giving precedence to values already set in the first file.
+    /// </summary>
+    /// <param name="newConfig">The new config file to be merged into the existing config set.</param>
+    private void MergeComponentDetectionConfig(ComponentDetectionConfigFile newConfig)
+    {
+        foreach ((var name, var value) in newConfig.Variables)
+        {
+            if (!this.componentDetectionConfig.Variables.ContainsKey(name))
+            {
+                this.componentDetectionConfig.Variables[name] = value;
+            }
+        }
+    }
+
     /// <summary>
     /// Reads the component detection config from a file path.
     /// </summary>

src/Microsoft.ComponentDetection.Orchestrator/Commands/BaseSettings.cs

@@ -37,6 +37,10 @@ public abstract class BaseSettings : CommandSettings
     [CommandOption("--Output")]
     public string Output { get; set; }
 
+    [Description("File path for a ComponentDetection.yml config file with more instructions for detection")]
+    [CommandOption("--ComponentDetectionConfigFile")]
+    public string ComponentDetectionConfigFile { get; set; }
+
     /// <inheritdoc />
     public override ValidationResult Validate()
     {

src/Microsoft.ComponentDetection.Orchestrator/Commands/ScanCommand.cs

@@ -44,7 +44,7 @@ public ScanCommand(
     public override async Task<int> ExecuteAsync(CommandContext context, ScanSettings settings)
     {
         this.fileWritingService.Init(settings.Output);
-        await this.componentDetectionConfigFileService.InitAsync(settings.SourceDirectory.FullName);
+        await this.componentDetectionConfigFileService.InitAsync(settings.ComponentDetectionConfigFile, settings.SourceDirectory.FullName);
         var result = await this.scanExecutionService.ExecuteScanAsync(settings);
         this.WriteComponentManifest(settings, result);
         return 0;