Add trace log message when failing to find Env Var

src/Bicep.Core.IntegrationTests/ParameterFileTests.cs

@@ -94,9 +94,37 @@ public void Parameters_file_cannot_reference_non_existing_env_variable()
 
         result.ExcludingLinterDiagnostics().Should().HaveDiagnostics(new[]{
                 ("BCP338", DiagnosticLevel.Error,
-                "Failed to evaluate parameter \"stringEnvVariable\": Environment variable does not exist, and no default value set")});
+                "Failed to evaluate parameter \"fromEnv\": Environment variable \"stringEnvVariable\" does not exist, and no default value set.")});
     }
 
+    [TestMethod]
+    public void Parameters_file_cannot_reference_non_existing_env_variable_verbose()
+    {
+        var result = CompilationHelper.CompileParams(
+("bicepconfig.json", """
+{
+  "analyzers": {
+    "core": {
+      "rules": {
+      },
+      "verbose": true
+    }
+  }
+}
+"""),
+("parameters.bicepparam", @"
+using 'foo.bicep'
+param fromEnv=readEnvironmentVariable('stringEnvVariable')
+"),
+("foo.bicep", @"param fromEnv string"));
+
+        result.ExcludingLinterDiagnostics().Should().HaveDiagnostics(new[]{
+                ("BCP338", DiagnosticLevel.Error,
+                "Failed to evaluate parameter \"fromEnv\": Environment variable \"stringEnvVariable\" does not exist, and no default value set."),
+                ("Bicepparam ReadEnvironmentVariable function", DiagnosticLevel.Info,
+                "Available environment variables are: "
+                )});
+    }
     [TestMethod]
     public void Parameters_file_can_use_variables()
     {

src/Bicep.Core.UnitTests/Utils/TestEnvironment.cs

@@ -19,4 +19,7 @@ public static IEnvironment Create(params (string key, string? value)[] variables
 
     public string? GetVariable(string variable)
         => variables.TryGetValue(variable, out var value) ? value : null;
+
+    public IEnumerable<string> GetVariableNames()
+        => variables.Keys;
 }

src/Bicep.Core/Semantics/Namespaces/SystemNamespaceType.cs

@@ -10,6 +10,7 @@
 using Bicep.Core.Features;
 using Bicep.Core.FileSystem;
 using Bicep.Core.Intermediate;
+using Bicep.Core.Analyzers.Linter;
 using Bicep.Core.Modules;
 using Bicep.Core.Navigation;
 using Bicep.Core.Parsing;
@@ -1155,9 +1156,26 @@ private static FunctionResult ReadEnvironmentVariableResultBuilder(SemanticModel
                 }
                 else
                 {
+                    //log available environment variables if verbose logging is enabled
+                    if(model.Configuration.Analyzers.GetValue(LinterAnalyzer.LinterEnabledSetting, false) && model.Configuration.Analyzers.GetValue(LinterAnalyzer.LinterVerboseSetting, false)) {
+                        var availableEnvironmentVariables = model.Environment.GetVariableNames();
+                        diagnostics.Write(
+                            new Diagnostic(
+                                arguments[0].Span,
+                                DiagnosticLevel.Info,
+                                "Bicepparam ReadEnvironmentVariable function",
+                                "Available environment variables are: " + string.Join(", ", model.Environment.GetVariableNames()),
+                                null)
+                        );                     
+                    }
+
                     //error to fail the build-param with clear message of the missing env var name
-                    return new(ErrorType.Create(DiagnosticBuilder.ForPosition(arguments[0]).FailedToEvaluateParameter(envVariableName,
-                    "Environment variable does not exist, and no default value set")));
+                    var paramAssignmentDefinition = model.Root.ParameterAssignments.Where(
+                        p => p.DeclaringParameterAssignment.Value.Span.Position == functionCall.Span.Position
+                    ).FirstOrDefault();
+                    var paramName = paramAssignmentDefinition?.Name ?? "";
+                    return new(ErrorType.Create(DiagnosticBuilder.ForPosition(arguments[0]).FailedToEvaluateParameter(paramName,
+                    $"Environment variable \"{envVariableName}\" does not exist, and no default value set.")));
                 }
             }
             return new(TypeFactory.CreateStringLiteralType(envVariableValue),

src/Bicep.Core/Utils/Environment.cs

@@ -6,4 +6,7 @@ public class Environment : IEnvironment
 {
     public string? GetVariable(string variable)
         => System.Environment.GetEnvironmentVariable(variable);
+
+    public IEnumerable<string> GetVariableNames()
+        => System.Environment.GetEnvironmentVariables().Keys.Cast<string>();
 }

src/Bicep.Core/Utils/IEnvironment.cs

@@ -5,4 +5,6 @@ namespace Bicep.Core.Utils;
 public interface IEnvironment
 {
     string? GetVariable(string variable);
+
+    IEnumerable<string> GetVariableNames();
 }