helper/resource: Added TF_LOG environment variable passthrough to T…

…erraform during acceptance testing on versions 0.15 and later

Reference: hashicorp/terraform-exec#291
Reference: #992

This allows the acceptance testing framework to appropriately set the `TF_LOG` environment variable via `terraform-exec`, if Terraform is version 0.15 or later. Otherwise, defaults to `TRACE` similar to before when `TF_ACC_LOG_PATH` or `TF_LOG_PATH_MASK` environment variables are set.

.changelog/pending.txt

@@ -0,0 +1,3 @@
+```release-note:enhancement
+helper/resource: Added `TF_LOG` environment variable passthrough to Terraform during acceptance testing on versions 0.15 and later
+```

internal/logging/keys.go

@@ -31,6 +31,9 @@ const (
 	// The TestStep number of the test being executed. Starts at 1.
 	KeyTestStepNumber = "test_step_number"
 
+	// The Terraform CLI logging level (TF_LOG) for used for an acceptance test.
+	KeyTestTerraformLogLevel = "test_terraform_log_level"
+
 	// The path to the Terraform CLI logging file used for an acceptance test.
 	//
 	// This should match where the rest of the acceptance test logs are going

internal/plugintest/environment_variables.go

@@ -18,6 +18,18 @@ const (
 	// If TF_LOG_PATH_MASK is set, it takes precedence over this value.
 	EnvTfAccLogPath = "TF_ACC_LOG_PATH"
 
+	// Environment variable with level to filter Terraform logs during
+	// acceptance testing. This value sets TF_LOG in a safe manner when
+	// executing Terraform CLI commands, which would otherwise be ignored
+	// since it could interfere with how the underlying execution is performed.
+	//
+	// If not set, but TF_ACC_LOG_PATH or TF_LOG_PATH_MASK is set, it defaults
+	// to TRACE. If Terraform CLI is version 0.14 or earlier, it will have no
+	// separate affect from the TF_ACC_LOG_PATH or TF_LOG_PATH_MASK behavior,
+	// as those earlier versions of Terraform are unreliable with the logging
+	// level being outside TRACE.
+	EnvTfLog = "TF_LOG"
+
 	// Environment variable with path containing the string %s, which is
 	// replaced with the test name, to save separate Terraform logs during
 	// acceptance testing. This value sets TF_LOG_PATH in a safe manner when

internal/plugintest/helper.go

@@ -139,6 +139,28 @@ func (h *Helper) NewWorkingDir(ctx context.Context, t TestControl) (*WorkingDir,
 		return nil, fmt.Errorf("unable to disable terraform-exec provider verification: %w", err)
 	}
 
+	if tfLog := os.Getenv(EnvTfLog); tfLog != "" {
+		logging.HelperResourceTrace(
+			ctx,
+			fmt.Sprintf("Setting terraform-exec log level via %s environment variable, if Terraform CLI is version 0.15 or later", EnvTfLog),
+			map[string]interface{}{logging.KeyTestTerraformLogLevel: tfLog},
+		)
+
+		err := tf.SetLog(tfLog)
+
+		if err != nil {
+			if !errors.As(err, new(*tfexec.ErrVersionMismatch)) {
+				return nil, fmt.Errorf("unable to set terraform-exec log level (%s): %w", tfLog, err)
+			}
+
+			logging.HelperResourceWarn(
+				ctx,
+				fmt.Sprintf("Unable to set terraform-exec log level via %s environment variable, as Terraform CLI is version 0.14 or earlier. It will default to TRACE.", EnvTfLog),
+				map[string]interface{}{logging.KeyTestTerraformLogLevel: "TRACE"},
+			)
+		}
+	}
+
 	var logPath, logPathEnvVar string
 
 	if tfAccLogPath := os.Getenv(EnvTfAccLogPath); tfAccLogPath != "" {