explain TF local exec error detection/parsing

automation/terraformActions.go

@@ -410,12 +410,24 @@ func monitorTerraformApplyProgress(
 			} else {
 				//fmt.Printf("NOT PARSE %s\n", lineWithoutAnsiEscapes)
 
+				// Check if there is a line which contains an exec error.
+				// If there is such a line, it won't contain the module that failed, just the command that failed.
+				// so we have to look back in the log to find the last time that command was mentioned, which should hit the
+				// line which has the module / resource name on it.
+				// So for example we could find a line:
+				//
+				// Error: Error running command './ansible-playbook-wrapper --private-key '/usr/lib/rootsystem/ssh/severgarden_builtin_ed22519' -i '167.71.175.207,' -u root -e 'domain=greenhouseusers.com arch=amd64' playbook.yml': exit status 4. Output:
+				//
+				// Then we look back in the log for any line which contains that command, and we find:
+				//
+				// module.ansible-threshold-server.null_resource.ansible_playbook[0] (local-exec): Executing: ["/bin/sh" "-c" "./ansible-playbook-wrapper --private-key '/usr/lib/rootsystem/ssh/severgarden_builtin_ed22519' -i '167.71.175.207,' -u root -e 'domain=greenhouseusers.com arch=amd64' playbook.yml"]
+				//
 				matches := terraformExecErrorRegex.FindStringSubmatch(lineWithoutAnsiEscapes)
 				if matches != nil {
 					commandThatFailed := matches[1]
 					previousLineContainingCommandThatFailed := ""
 					for i, previousLine := range logLinesWithoutAnsiEscapes {
-						if i < len(logLinesWithoutAnsiEscapes.length-2) && strings.Contains(previousLine, commandThatFailed) {
+						if i < len(logLinesWithoutAnsiEscapes)-2 && strings.Contains(previousLine, commandThatFailed) {
 							previousLineContainingCommandThatFailed = previousLine
 						}
 					}