Fix R CMD check failures: suppress GLib and libfluidsynth non-critical log messages

[Copilot]

In restricted build environments (e.g. r-universe) where HOME is inaccessible, the message "Home directory not accessible: Permission denied" appears on stderr during R CMD check. This message comes from GLib (via g_warning()), which libfluidsynth depends on as its OS abstraction layer. When GLib lazily initializes user directory paths (triggered by the first libfluidsynth API call), it attempts g_get_home_dir() and logs the warning directly to stderr, bypassing R's suppressMessages() entirely. R CMD check treats this uncapturable stderr output as a broken startup message and cascades failures across multiple check steps.

Changes in src/init.c

• logging_callback: only emits output for FLUID_PANIC and FLUID_ERR; FLUID_WARN, FLUID_INFO, and FLUID_DBG are silently dropped. Critical errors still surface; operational/informational chatter does not.
• Register FLUID_DBG: added fluid_set_log_function(FLUID_DBG, logging_callback, NULL) so all libfluidsynth log levels are intercepted by our handler rather than falling through to libfluidsynth's default stderr handler.
• GLib log handler: added glib_log_suppress() installed via g_log_set_handler() for the default GLib log domain at WARNING | MESSAGE | INFO | DEBUG levels. This intercepts GLib's "Home directory not accessible" warning before it reaches stderr. G_LOG_LEVEL_CRITICAL and G_LOG_LEVEL_ERROR are deliberately not suppressed. Guarded by #ifdef HAVE_GLIB.

// Suppress non-critical libfluidsynth messages
static void logging_callback(int level, const char *message, void *data){
  if(level <= FLUID_ERR){
    REprintf("[FluidSynth] %s\n", message);
  }
}

// Suppress non-critical GLib messages (e.g. "Home directory not accessible")
#ifdef HAVE_GLIB
static void glib_log_suppress(const gchar *log_domain, GLogLevelFlags log_level,
                               const gchar *message, gpointer user_data){
  (void)log_domain; (void)log_level; (void)message; (void)user_data;
}
#endif

Changes in configure

• Added a check that tests whether glib.h is accessible using the fluidsynth pkg-config cflags (which already include GLib include paths on Linux/Mac, since fluidsynth depends on GLib). Sets -DHAVE_GLIB when GLib headers are found.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>R CMD check problems</issue_title>
<issue_description>:wave: @jeroen! https://ropensci.r-universe.dev/builds indicates

* checking whether startup messages can be suppressed ... NOTE
Home directory not accessible: Permission denied

It looks like this package (or a package it requires) has a startup
message which cannot be suppressed: see ?packageStartupMessage.
* checking dependencies in R code ... NOTE
Home directory not accessible: Permission denied
* checking S3 generic/method consistency ... WARNING
Home directory not accessible: Permission denied
See section ‘Generic functions and methods’ in the ‘Writing R
Extensions’ manual.
* checking replacement functions ... WARNING
Home directory not accessible: Permission denied
The argument of a replacement function which corresponds to the right
hand side must be named ‘value’.
* checking foreign function calls ... NOTE
Home directory not accessible: Permission denied
See chapter ‘System and foreign language interfaces’ in the ‘Writing R
Extensions’ manual.
* checking R code for possible problems ... NOTE
Home directory not accessible: Permission denied
* checking Rd files ... OK
* checking Rd metadata ... OK
* checking Rd cross-references ... OK
* checking for missing documentation entries ... WARNING
Home directory not accessible: Permission denied
All user-level objects in a package should have documentation entries.
See chapter ‘Writing R documentation files’ in the ‘Writing R
Extensions’ manual.
* checking for code/documentation mismatches ... WARNING
Home directory not accessible: Permission denied
Home directory not accessible: Permission denied
Home directory not accessible: Permission denied
* checking Rd \usage sections ... NOTE
Home directory not accessible: Permission denied
The \usage entries for S3 methods should use the \method markup and not
their full name.
See chapter ‘Writing R documentation files’ in the ‘Writing R
Extensions’ manual.

```</issue_description>

<agent_instructions>Does this package try to write to the home directory?</agent_instructions>

## Comments on the Issue (you are @copilot in this section)

<comments>
</comments>

• Fixes R CMD check problems #4

---

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[jeroen]

@copilot why does new_fluid_settings write in the home directory? What is it writing? Can we set it to write elsewhere?

[Copilot]

@copilot why does new_fluid_settings write in the home directory? What is it writing? Can we set it to write elsewhere?

The message doesn't come from libfluidsynth itself — it comes from GLib (which fluidsynth depends on). When any GLib function is first called (e.g. triggered by new_fluid_settings()), GLib lazily initializes user directory paths by calling g_get_home_dir(). When the home directory is inaccessible (as on the r-universe build server), GLib emits g_warning("Home directory not accessible: ...") which goes directly to stderr, bypassing R's message routing and suppressMessages() entirely.

It reads (not writes) the home directory — it's looking for GLib's standard user config/data directories.

There's no fluidsynth API to prevent this; fluidsynth doesn't expose control over GLib's own directory lookups.

Fixed in commit 3331970 by installing a GLib log handler at R_init_fluidsynth() startup that silently drops GLib WARNING/MESSAGE/INFO/DEBUG messages from the default domain. The configure script now checks for GLib header availability (which is guaranteed on Linux/Mac since fluidsynth depends on GLib) and sets -DHAVE_GLIB. CRITICAL and FATAL GLib messages are deliberately not suppressed.

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