Limit Natvis namespace variants to two ABI tags (#5877)

The generator wrote a namespace entry for every combination of ABI tags,
so nlohmann_json.natvis doubled with each new tag. With the 12 tags on
develop it had reached 57.9 MB, and one more tag would push it past
GitHub's 100 MB file limit. It now covers the default namespace, every
single tag, and every pair of tags (versioned and unversioned), which is
158 entries / 1 MB with 12 tags.

Taken over from #5868. Refs #5863.

Signed-off-by: Kartikey <kg704925@gmail.com>
Signed-off-by: Niels Lohmann <mail@nlohmann.me>
Co-authored-by: Kartikey <kg704925@gmail.com>

docs/mkdocs/docs/home/debugging.md

@@ -10,6 +10,9 @@ at its root, a [Natvis](https://learn.microsoft.com/en-us/visualstudio/debugger/
 file that gives `json`/`ordered_json` values a friendly, key/value debugger view instead of showing raw internal
 fields, when debugging with the MSVC debug engine (`cppvsdbg`) in Visual Studio or VS Code.
 
+The checked-in visualizers cover namespace variants with zero, one, or two ABI tags. Configurations with three or more
+ABI tags are not covered and may show raw internal fields instead.
+
 Debug engines that wrap LLDB instead of the MSVC debug engine (for example, `codelldb` in VS Code) only have
 partial/experimental Natvis support, and commonly fall back to showing raw internal fields even with the
 `.natvis` file present. Switching to `cppvsdbg` where available, or checking your debug extension's own Natvis

tools/generate_natvis/README.md

@@ -1,6 +1,10 @@
 # generate_natvis.py
 
-Generate the Natvis debugger visualization file for all supported namespace combinations.
+Generate the Natvis debugger visualization file for namespace combinations with up to two ABI tags.
+
+The checked-in `nlohmann_json.natvis` covers the default namespace (no ABI tags), every single ABI tag, and every pair
+of ABI tags, with both versioned and unversioned namespace variants. Configurations that enable three or more ABI tags
+are not covered by this reduced file.
 
 The ABI tag list and the library version are parsed from
 `include/nlohmann/detail/abi_macros.hpp`, so this script must be re-run (via

tools/generate_natvis/generate_natvis.py

@@ -78,8 +78,8 @@ if __name__ == '__main__':
     version = '_v' + (args.version or derived_version).replace('.', '_')
     inline_namespaces = []
 
-    # generate all combinations of inline namespace names
-    for n in range(0, len(abi_tags) + 1):
+    # generate namespace names for up to two ABI tags
+    for n in range(0, min(len(abi_tags), 2) + 1):
         for tags in itertools.combinations(abi_tags, n):
             ns = abi_prefix + ''.join(tags)
             inline_namespaces += [ns, ns + version]