Auto merge of #16687 - aneeshusa:keep-stable-rustc-during-clean-nightlies, r=mbrubeck

Keep stable rustc versions in `clean-nightlies`

Check the `rust-stable-version` file to keep the last n
versions of both the nightly and the stable compiler.

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---
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- [ ] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [x] These changes fix #16675 (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 should be checked manually

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python/servo/bootstrap_commands.py

@@ -290,9 +290,13 @@ class MachCommands(CommandBase):
                      default='1',
                      help='Keep up to this many most recent nightlies')
     def clean_nightlies(self, force=False, keep=None):
-        rust_current = self.rust_version()
+        self.set_use_stable_rust(False)
+        rust_current_nightly = self.rust_version()
+        self.set_use_stable_rust(True)
+        rust_current_stable = self.rust_version()
         cargo_current = self.cargo_build_id()
-        print("Current Rust version: {}".format(rust_current))
+        print("Current Rust nightly version: {}".format(rust_current_nightly))
+        print("Current Rust stable version: {}".format(rust_current_stable))
         print("Current Cargo version: {}".format(cargo_current))
         to_keep = {
             'rust': set(),
@@ -300,13 +304,17 @@ class MachCommands(CommandBase):
         }
         if int(keep) == 1:
             # Optimize keep=1 case to not invoke git
-            to_keep['rust'].add(rust_current)
+            to_keep['rust'].add(rust_current_nightly)
+            to_keep['rust'].add(rust_current_stable)
             to_keep['cargo'].add(cargo_current)
         else:
-            for tool in ["rust", "cargo"]:
-                commit_file = '{}-commit-hash'.format(tool)
+            for tool, version_files in {
+                'rust': ['rust-commit-hash', 'rust-stable-version'],
+                'cargo': ['cargo-commit-hash'],
+            }.items():
+                for version_file in version_files:
                     cmd = subprocess.Popen(
-                    ['git', 'log', '--oneline', '--no-color', '-n', keep, '--patch', commit_file],
+                        ['git', 'log', '--oneline', '--no-color', '-n', keep, '--patch', version_file],
                         stdout=subprocess.PIPE,
                         universal_newlines=True
                     )