Started reintegrating what used to be called user bugs; they're now called programmer errors. We'll create a much more systematic approach to them. Implemented on macOS.

common/meson.build

@@ -2,4 +2,5 @@
 
 libui_sources += [
 	'common/init.c',
+	'common/programmererror.c',
 ]

common/programmererror.c

@@ -0,0 +1,41 @@
+// 12 may 2019
+#include <stdarg.h>
+#include <stdio.h>
+#include "ui.h"
+#include "uipriv.h"
+
+static const char *messages[] = {
+	[uiprivProgrammerErrorWrongStructSize] = "wrong size %zu for %s",
+	[uiprivProgrammerErrorIndexOutOfRange] = "index %d out of range in %s()",
+};
+
+static void prepareProgrammerError(char *buf, int size, unsigned int which, va_list ap)
+{
+	int n;
+
+	if (which >= uiprivNumProgrammerErrors) {
+		// TODO
+	}
+	n = vsnprintf(buf, size, messages[which], ap);
+	if (n < 0) {
+		// TODO
+	}
+	if (n >= size) {
+		// TODO
+		buf[size - 4] = '.';
+		buf[size - 3] = '.';
+		buf[size - 2] = '.';
+		buf[size - 1] = '\0';
+	}
+}
+
+void uiprivProgrammerError(unsigned int which, ...)
+{
+	va_list ap;
+	char buf[256];
+
+	va_start(ap, which);
+	prepareProgrammerError(buf, 256, which, ap);
+	va_end(ap);
+	uiprivSysProgrammerError(buf);
+}

common/uipriv.h

@@ -10,6 +10,18 @@ extern int uiprivSysInit(void *options, uiInitError *err);
 extern int uiprivInitReturnError(uiInitError *err, const char *msg);
 extern int uiprivInitReturnErrorf(uiInitError *err, const char *msg, ...);
 
+// programmererror.c
+enum {
+	uiprivProgrammerErrorWrongStructSize,		// arguments: size_t badSize, const char *structName
+	uiprivProgrammerErrorIndexOutOfRange,	// arguments: int badIndex, __func__
+	uiprivNumProgrammerErrors,
+};
+extern void uiprivProgrammerError(unsigned int which, ...);
+extern void uiprivSysProgrammerError(const char *msg);
+#define uiprivProgrammerErrorPrefix "libui programmer error"
+// TODO add debugging advice?
+#define uiprivProgrammerErrorAdvice "This likely means you are using libui incorrectly. Check your source code and try again. If you have received this warning in error, contact the libui authors."
+
 #ifdef __cplusplus
 }
 #endif

darwin/main.m

@@ -1,4 +1,5 @@
 // 20 april 2019
+#import <stdlib.h>
 #import "uipriv_darwin.h"
 
 @interface uiprivApplication : NSApplication
@@ -97,3 +98,13 @@ void uiQueueMain(void (*f)(void *data), void *data)
 	// the signature of f matches dispatch_function_t
 	dispatch_async_f(dispatch_get_main_queue(), data, f);
 }
+
+void uiprivSysProgrammerError(const char *msg)
+{
+	NSLog(@"*** %s: %s. %s", uiprivProgrammerErrorPrefix, msg, uiprivProgrammerErrorAdvice);
+	// TODO either find an appropriate exception for each message or use a custom exception name
+	[NSException raise:NSInvalidArgumentException
+		format:@"%s: %s", uiprivProgrammerErrorPrefix, msg];
+	// TODO break into the debugger?
+	abort();		// we shouldn't reach here
+}