Auto merge of #28463 - mkg20001:nixos-mach, r=jdm

add NixOS support to mach and automatically re-launch mach in nix-shell

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This is a followup for #28454 which adds nixos support directly to mach, saving the user from typing `nix-shell` everytime

---
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- [ ] `./mach build -d` does not report any errors
- [ ] `./mach test-tidy` does not report any errors
- [ ] These changes fix #___ (GitHub issue number if applicable)

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- [ ] There are tests for these changes OR
- [x] These changes do not require tests because they just extend mach

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python/servo/bootstrap.py

@@ -383,6 +383,7 @@ def get_linux_distribution():
         'debian gnu/linux',
         'fedora',
         'void',
+        'nixos',
     ]:
         raise Exception('mach bootstrap does not support %s, please file a bug' % distrib)
 
@@ -398,6 +399,15 @@ def bootstrap(context, force=False, specific=None):
     elif "linux-gnu" in host_triple():
         distrib, version = get_linux_distribution()
 
+        if distrib.lower() == 'nixos':
+            print('NixOS does not need bootstrap, it will automatically enter a nix-shell')
+            print('Just run ./mach build')
+            print('')
+            print('You will need to run a nix-shell if you are trying to run any of the built binaries')
+            print('To enter the nix-shell manually use:')
+            print('  $ nix-shell etc/shell.nix')
+            return
+
         context.distro = distrib
         context.distro_version = version
         bootstrapper = LINUX_SPECIFIC_BOOTSTRAPPERS.get(specific, linux)