bootstrap: don't call support_xz in hot-path

src/bootstrap/bootstrap.py

@@ -331,17 +331,6 @@ def __init__(self):
         self.use_vendored_sources = ''
         self.verbose = False
 
-        def support_xz():
-            try:
-                with tempfile.NamedTemporaryFile(delete=False) as temp_file:
-                    temp_path = temp_file.name
-                with tarfile.open(temp_path, "w:xz") as tar:
-                    pass
-                return True
-            except tarfile.CompressionError:
-                return False
-
-        self.tarball_suffix = '.tar.xz' if support_xz() else '.tar.gz'
 
     def download_stage0(self):
         """Fetch the build system for Rust, written in Rust
@@ -356,19 +345,30 @@ def download_stage0(self):
         rustc_channel = self.rustc_channel
         cargo_channel = self.cargo_channel
 
+        def support_xz():
+            try:
+                with tempfile.NamedTemporaryFile(delete=False) as temp_file:
+                    temp_path = temp_file.name
+                with tarfile.open(temp_path, "w:xz") as tar:
+                    pass
+                return True
+            except tarfile.CompressionError:
+                return False
+
         if self.rustc().startswith(self.bin_root()) and \
                 (not os.path.exists(self.rustc()) or
                  self.program_out_of_date(self.rustc_stamp())):
             if os.path.exists(self.bin_root()):
                 shutil.rmtree(self.bin_root())
+            tarball_suffix = '.tar.xz' if support_xz() else '.tar.gz'
             filename = "rust-std-{}-{}{}".format(
-                rustc_channel, self.build, self.tarball_suffix)
+                rustc_channel, self.build, tarball_suffix)
             pattern = "rust-std-{}".format(self.build)
-            self._download_stage0_helper(filename, pattern)
+            self._download_stage0_helper(filename, pattern, tarball_suffix)
 
             filename = "rustc-{}-{}{}".format(rustc_channel, self.build,
-                                              self.tarball_suffix)
-            self._download_stage0_helper(filename, "rustc")
+                                              tarball_suffix)
+            self._download_stage0_helper(filename, "rustc", tarball_suffix)
             self.fix_executable("{}/bin/rustc".format(self.bin_root()))
             self.fix_executable("{}/bin/rustdoc".format(self.bin_root()))
             with output(self.rustc_stamp()) as rust_stamp:
@@ -379,20 +379,21 @@ def download_stage0(self):
             # the system MinGW ones.
             if "pc-windows-gnu" in self.build:
                 filename = "rust-mingw-{}-{}{}".format(
-                    rustc_channel, self.build, self.tarball_suffix)
-                self._download_stage0_helper(filename, "rust-mingw")
+                    rustc_channel, self.build, tarball_suffix)
+                self._download_stage0_helper(filename, "rust-mingw", tarball_suffix)
 
         if self.cargo().startswith(self.bin_root()) and \
                 (not os.path.exists(self.cargo()) or
                  self.program_out_of_date(self.cargo_stamp())):
+            tarball_suffix = '.tar.xz' if support_xz() else '.tar.gz'
             filename = "cargo-{}-{}{}".format(cargo_channel, self.build,
-                                              self.tarball_suffix)
-            self._download_stage0_helper(filename, "cargo")
+                                              tarball_suffix)
+            self._download_stage0_helper(filename, "cargo", tarball_suffix)
             self.fix_executable("{}/bin/cargo".format(self.bin_root()))
             with output(self.cargo_stamp()) as cargo_stamp:
                 cargo_stamp.write(self.date)
 
-    def _download_stage0_helper(self, filename, pattern):
+    def _download_stage0_helper(self, filename, pattern, tarball_suffix):
         cache_dst = os.path.join(self.build_dir, "cache")
         rustc_cache = os.path.join(cache_dst, self.date)
         if not os.path.exists(rustc_cache):
@@ -402,7 +403,7 @@ def _download_stage0_helper(self, filename, pattern):
         tarball = os.path.join(rustc_cache, filename)
         if not os.path.exists(tarball):
             get("{}/{}".format(url, filename), tarball, verbose=self.verbose)
-        unpack(tarball, self.tarball_suffix, self.bin_root(), match=pattern, verbose=self.verbose)
+        unpack(tarball, tarball_suffix, self.bin_root(), match=pattern, verbose=self.verbose)
 
     @staticmethod
     def fix_executable(fname):