Add a logging allocator that uses std.log (#8511)

test/compare_output.zig

@@ -599,4 +599,50 @@ pub fn addCases(cases: *tests.CompareOutputContext) void {
         \\emergency(c): 
         \\
     );
+
+    // It is required to override the log function in order to print to stdout instead of stderr
+    cases.add("std.heap.LoggingAllocator logs to std.log",
+        \\const std = @import("std");
+        \\
+        \\pub const log_level: std.log.Level = .debug;
+        \\
+        \\pub fn main() !void {
+        \\    var allocator_buf: [10]u8 = undefined;
+        \\    var fixedBufferAllocator = std.mem.validationWrap(std.heap.FixedBufferAllocator.init(&allocator_buf));
+        \\    const allocator = &std.heap.loggingAllocator(&fixedBufferAllocator.allocator).allocator;
+        \\
+        \\    var a = try allocator.alloc(u8, 10);
+        \\    a = allocator.shrink(a, 5);
+        \\    try std.testing.expect(a.len == 5);
+        \\    try std.testing.expectError(error.OutOfMemory, allocator.resize(a, 20));
+        \\    allocator.free(a);
+        \\}
+        \\
+        \\pub fn log(
+        \\    comptime level: std.log.Level,
+        \\    comptime scope: @TypeOf(.EnumLiteral),
+        \\    comptime format: []const u8,
+        \\    args: anytype,
+        \\) void {
+        \\    const level_txt = switch (level) {
+        \\        .emerg => "emergency",
+        \\        .alert => "alert",
+        \\        .crit => "critical",
+        \\        .err => "error",
+        \\        .warn => "warning",
+        \\        .notice => "notice",
+        \\        .info => "info",
+        \\        .debug => "debug",
+        \\    };
+        \\    const prefix2 = if (scope == .default) ": " else "(" ++ @tagName(scope) ++ "): ";
+        \\    const stdout = std.io.getStdOut().writer();
+        \\    nosuspend stdout.print(level_txt ++ prefix2 ++ format ++ "\n", args) catch return;
+        \\}
+    ,
+        \\debug: alloc - success - len: 10, ptr_align: 1, len_align: 0
+        \\debug: shrink - success - 10 to 5, len_align: 0, buf_align: 1
+        \\critical: expand - failure: OutOfMemory - 5 to 20, len_align: 0, buf_align: 1
+        \\debug: free - success - len: 5
+        \\
+    );
 }