support digger planfile (#1977)

* support digger planfile

Author: motatoes

docs/ce/howto/custom-commands.mdx

@@ -26,6 +26,7 @@ Digger makes the following environment variables available to custom commands:
 - `$DIGGER_OUT`
 - `$PR_BRANCH`
 - `$PROJECT_NAME`
+- `$DIGGER_PLANFILE` (the path where terraform plan file should be written)
 
 These can be used to achieve workflows like [infracost diff](/ce/howto/using-infracost)
 

libs/execution/execution.go

@@ -285,6 +285,12 @@ func (d DiggerExecutor) Plan() (*iac_utils.IacSummary, bool, bool, string, strin
 			slog.Info("Running command",
 				"command", step.Value,
 				"project", d.ProjectNamespace+"#"+d.ProjectName)
+			// setting additional env vars for run step
+			if d.RunEnvVars == nil {
+				d.RunEnvVars = make(map[string]string)
+			}
+			slog.Debug("adding plan file path to environment", "DIGGER_PLANFILE", d.PlanPathProvider.LocalPlanFilePath())
+			d.RunEnvVars["DIGGER_PLANFILE"] = d.PlanPathProvider.LocalPlanFilePath()
 			_, _, err := d.CommandRunner.Run(d.ProjectPath, step.Shell, commands, d.RunEnvVars)
 			if err != nil {
 				return nil, false, false, "", "", fmt.Errorf("error running command: %v", err)