Use `root.std_options` to override log behaviour (#99)

ziglang/zig#14181 changed the interface for overriding the log function.
Previously, you would define a public `root.log` function. Now, you
define a `root.std_options` namespace that has a `logFn` decl.

Signed-off-by: Aidan Oldershaw <aidan.oldershaw@gmail.com>

src/core/microzig.zig

@@ -48,35 +48,17 @@ pub const debug = @import("debug.zig");
 
 pub const mmio = @import("mmio.zig");
 
-// Allow app to override the os API layer
-pub const os = if (@hasDecl(app, "os"))
-    app.os
-else
-    struct {};
-
-// Allow app to override the panic handler
-pub const panic = if (@hasDecl(app, "panic"))
-    app.panic
-else
-    microzig_panic;
-
-// Conditionally export log_level if the app has it defined.
-usingnamespace if (@hasDecl(app, "log_level"))
+const options_override = if (@hasDecl(app, "std_options")) app.std_options else struct {};
+pub const std_options = struct {
+    pub usingnamespace options_override;
+
+    // Conditionally provide a default no-op logFn if app does not have one
+    // defined. Parts of microzig use the stdlib logging facility and
+    // compilations will now fail on freestanding systems that use it but do
+    // not explicitly set `root.std_options.logFn`
+    pub usingnamespace if (!@hasDecl(options_override, "logFn"))
         struct {
-        pub const log_level = app.log_level;
-    }
-else
-    struct {};
-
-// Conditionally export log() if the app has it defined.
-pub const log = if (@hasDecl(app, "log"))
-    app.log
-else
-    // log is a no-op by default. Parts of microzig use the stdlib logging
-    // facility and compilations will now fail on freestanding systems that
-    // use it but do not explicitly set `root.log`
-    struct {
-        fn log(
+            pub fn logFn(
                 comptime message_level: std.log.Level,
                 comptime scope: @Type(.EnumLiteral),
                 comptime format: []const u8,
@@ -87,7 +69,22 @@ else
                 _ = format;
                 _ = args;
             }
-    }.log;
+        }
+    else
+        struct {};
+};
+
+// Allow app to override the os API layer
+pub const os = if (@hasDecl(app, "os"))
+    app.os
+else
+    struct {};
+
+// Allow app to override the panic handler
+pub const panic = if (@hasDecl(app, "panic"))
+    app.panic
+else
+    microzig_panic;
 
 /// The microzig default panic handler. Will disable interrupts and loop endlessly.
 pub fn microzig_panic(message: []const u8, _: ?*std.builtin.StackTrace, _: ?usize) noreturn {