feat: add namespace support to Writer

[ianprime0509]

TODO: I need to take another look over this before merging it to make sure I didn't miss anything (and possibly add more tests aside from just the doctests added here).

---

Closes #40

In addition to the new namespace-aware functions, this commit brings several other enhancements:

• The element name has been removed as an argument of elementEnd. The writer now keeps track of the current open element automatically.
• Doctests have been added for all public writer functions.
• Doc comments have been added for all public writer functions.

[MFAshby]

Thanks! I'm trying it out.

I saw some odd behaviour in my app with elementEnd() where the namespace appears to be missing, notice the closing tag </:href>, which should be </D:href>:

<?xml version="1.0" encoding="UTF-8"?>
<D:multistatus xmlns:D="DAV:" xmlns:c="urn:ietf:params:xml:ns:carddav">
  <D:response>
    <D:href>/</:href>
    <D:propstat>
      <D:prop xmlns:z="DAV:">
        <z:current-user-principal><href>/principal/0192c59f-4894-7ecf-bb00-c2348efa927d/</href></:current-user-principal>
...

I wrote a quick test to try to narrow it down:

test "namespaceBug" {
    var raw = std.ArrayList(u8).init(std.testing.allocator);
    defer raw.deinit();
    const out = streamingOutput(raw.writer());
    var writer = out.writer(std.testing.allocator, .{ .indent = "  " });
    defer writer.deinit();

    try writer.bindNs("d", "foospace");
    try writer.elementStartNs("foospace", "root");
    try writer.elementStartNs("foospace", "child");
    try writer.text("Hello, Bug");
    try writer.elementEnd();
    try writer.elementEnd();

    try expectEqualStrings(
        \\<d:root xmlns:d="foospace">
        \\  <d:child>
        \\    Hello, Bug
        \\  </d:child>
        \\</d:root>
    , raw.items);
}

unfortunately the test crashes with a segfault

martin@martin-pinebook ~/d/zig-xml (bug) [1]> zig build test
test
└─ run test failure
Segmentation fault at address 0xffff84c90001
/home/martin/.zigvm/zig-linux-aarch64-0.14.0-dev.1550+4fba7336a/lib/compiler_rt/memcpy.zig:19:21: 0x117e648 in memcpy (compiler_rt)
            d[0] = s[0];
                    ^
/home/martin/.zigvm/zig-linux-aarch64-0.14.0-dev.1550+4fba7336a/lib/std/array_list.zig:926:42: 0x1075ee3 in appendSliceAssumeCapacity (test)
            @memcpy(self.items[old_len..][0..items.len], items);
                                         ^
/home/martin/dev/zig-xml/src/Writer.zig:792:45: 0x111d82b in addPrefixedString (test)
    writer.strings.appendSliceAssumeCapacity(prefix);
                                            ^
???:?:?: 0xffffc0320127 in ??? (???)
Unwind information for `???:0xffffc0320127` was not available, trace may be incomplete


error: while executing test 'Writer.test.namespaceBug', the following command terminated with signal 6 (expected exited with code 0):
/home/martin/dev/zig-xml/.zig-cache/o/92af64094809fc156d3b34b4e7253c6e/test --seed=0x5a53cded --cache-dir=/home/martin/dev/zig-xml/.zig-cache --listen=-
Build Summary: 1/3 steps succeeded; 1 failed; 56/56 tests passed
test transitive failure
└─ run test failure
error: the following build command failed with exit code 1:
/home/martin/dev/zig-xml/.zig-cache/o/15f27f5a52566fe6a27a9eef16e4586b/build /home/martin/.zigvm/zig-linux-aarch64-0.14.0-dev.1550+4fba7336a/zig /home/martin/.zigvm/zig-linux

[ianprime0509]

Thanks! That bug is an unfortunate consequence of my trying to be a bit too clever with memory management 😄 I pushed up a fix in e00a4a8, and added your example as a test case.