Your PrestaShop hook renders nothing, and nothing is logged
A module hook that returns an empty string looks exactly like a module hook that was never called. PrestaShop gives you nothing to tell them apart: no error, no log entry, no stack trace, no fallback text. The page renders fine. Your block is just absent. We spent three releases of one module chasing this, and the cause turned out to be three different mechanisms stacked on top of each other.…
When a module hook returns an empty string, it appears identical to a hook that was never called. PrestaShop provides no indication of this discrepancy, leaving users with no error messages, log entries, stack traces, or fallback text. The page renders correctly, but the block remains absent. This issue plagued one module over three releases until a root cause analysis revealed three mechanisms stacked on top of each other, each capable of silently rendering output.
The setup involved registering the displayHeader hook and rendering a small template containing a script block for a public site key and a style block to hide a third-party badge. The code assigned variables and attempted to display the template. However, the module hook was swallowed by core, which caught exceptions and returned an empty string without logging or tracing the error. This design choice, while sensible, lacks debugging value.
To debug the issue, the code was modified to catch Throwable exceptions, log the error message, file, and line number, and provide a detailed HTML comment. This allowed the log entry to persist even after the page was gone, making it easier to identify the problem. The HTML comment remained visible in view-source mode, even when filters removed script and style tags.
The first mechanism that rendered the output invisible was core swallowing the exception. The second mechanism was a syntax error in the template's CSS. With the try/catch block in place, the log revealed the issue as a failed template compilation. The offending line contained a CSS property with an invalid structure, causing Smarty to choke on the syntax error and fail to compile the entire file.
The third mechanism was using a deprecated nofilter directive in inline JavaScript, which conflicted with PrestaShop's integration checklist requirements and resulted in a non-compilable template.
The solution involved wrapping every module hook that renders a template in a try/catch block that catches Throwable exceptions, logs the error, and provides a detailed HTML comment. This change ensures that all failures, regardless of the cause, are logged and visible in the comment. Additionally, it is recommended to use the documented escaper function for values used in inline JavaScript and follow the platform's template compilation policies to avoid silent failures on managed hosts.
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