Rollup merge of rust-lang#93885 - Badel2:error-download-ci-llvm, r=Ma…

…rk-Simulacrum

bootstrap.py: Suggest disabling download-ci-llvm option if url fails to download

I got an error when trying to build the compiler using an old commit, and it turns out it was because the option `download-ci-llvm` was implicitly set to true. So this pull request tries to add a help message for other people that may run into the same problem.

To reproduce my error:

```
git checkout 8d7707f
./x.py test
[...]
spurious failure, trying again
downloading https://ci-artifacts.rust-lang.org/rustc-builds/db002a06ae9154a35d410550bc5132df883d7baa/rust-dev-nightly-x86_64-unknown-linux-gnu.tar.xz
curl: (22) The requested URL returned error: 404

failed to run: curl -# -y 30 -Y 10 --connect-timeout 30 --retry 3 -Sf -o /tmp/tmp8g13rb4n https://ci-artifacts.rust-lang.org/rustc-builds/db002a06ae9154a35d410550bc5132df883d7baa/rust-dev-nightly-x86_64-unknown-linux-gnu.tar.xz
Build completed unsuccessfully in 0:00:46
```

This is my `config.toml`:

```
# Includes one of the default files in src/bootstrap/defaults
profile = "compiler"
changelog-seen = 2

[rust]
debug = true
```

To reproduce an error with this branch:

Change line 618 of bootstrap.py to
```
        url = "rustc-builds-error404/{}".format(llvm_sha)
```

Delete llvm and cached tarball, and set `llvm.download-ci-llvm=true` in config.toml.

```
./x.py test
[...]
spurious failure, trying again
downloading https://ci-artifacts.rust-lang.org/rustc-builds-error404/719b04ca99be0c78e09a8ec5e2eda082a5d8ccae/rust-dev-nightly-x86_64-unknown-linux-gnu.tar.xz
curl: (22) The requested URL returned error: 404

failed to run: curl -# -y 30 -Y 10 --connect-timeout 30 --retry 3 -Sf -o /tmp/tmpesl1ydvo https://ci-artifacts.rust-lang.org/rustc-builds-error404/719b04ca99be0c78e09a8ec5e2eda082a5d8ccae/rust-dev-nightly-x86_64-unknown-linux-gnu.tar.xz
error: failed to download llvm from ci
help: old builds get deleted after a certain time
help: if trying to compile an old commit of rustc, disable `download-ci-llvm` in config.toml:

[llvm]
download-ci-llvm = false

Build completed unsuccessfully in 0:00:01
```

Regarding the implementation, I expected to be able to use a try/catch block in `_download_ci_llvm`, but the `run` function calls `sys.exit` instead of raising an exception so that's not possible. Also, suggestions for better wording of the help message are welcome.

src/bootstrap/bootstrap.py

@@ -63,7 +63,7 @@ def support_xz():
     except tarfile.CompressionError:
         return False
 
-def get(base, url, path, checksums, verbose=False, do_verify=True):
+def get(base, url, path, checksums, verbose=False, do_verify=True, help_on_error=None):
     with tempfile.NamedTemporaryFile(delete=False) as temp_file:
         temp_path = temp_file.name
 
@@ -82,7 +82,7 @@ def get(base, url, path, checksums, verbose=False, do_verify=True):
                         print("ignoring already-download file",
                             path, "due to failed verification")
                     os.unlink(path)
-        download(temp_path, "{}/{}".format(base, url), True, verbose)
+        download(temp_path, "{}/{}".format(base, url), True, verbose, help_on_error=help_on_error)
         if do_verify and not verify(temp_path, sha256, verbose):
             raise RuntimeError("failed verification")
         if verbose:
@@ -95,17 +95,17 @@ def get(base, url, path, checksums, verbose=False, do_verify=True):
             os.unlink(temp_path)
 
 
-def download(path, url, probably_big, verbose):
+def download(path, url, probably_big, verbose, help_on_error=None):
     for _ in range(0, 4):
         try:
-            _download(path, url, probably_big, verbose, True)
+            _download(path, url, probably_big, verbose, True, help_on_error=help_on_error)
             return
         except RuntimeError:
             print("\nspurious failure, trying again")
-    _download(path, url, probably_big, verbose, False)
+    _download(path, url, probably_big, verbose, False, help_on_error=help_on_error)
 
 
-def _download(path, url, probably_big, verbose, exception):
+def _download(path, url, probably_big, verbose, exception, help_on_error=None):
     if probably_big or verbose:
         print("downloading {}".format(url))
     # see https://serverfault.com/questions/301128/how-to-download
@@ -126,7 +126,8 @@ def _download(path, url, probably_big, verbose, exception):
              "--connect-timeout", "30",  # timeout if cannot connect within 30 seconds
              "--retry", "3", "-Sf", "-o", path, url],
             verbose=verbose,
-            exception=exception)
+            exception=exception,
+            help_on_error=help_on_error)
 
 
 def verify(path, expected, verbose):
@@ -167,7 +168,7 @@ def unpack(tarball, tarball_suffix, dst, verbose=False, match=None):
     shutil.rmtree(os.path.join(dst, fname))
 
 
-def run(args, verbose=False, exception=False, is_bootstrap=False, **kwargs):
+def run(args, verbose=False, exception=False, is_bootstrap=False, help_on_error=None, **kwargs):
     """Run a child program in a new process"""
     if verbose:
         print("running: " + ' '.join(args))
@@ -178,6 +179,8 @@ def run(args, verbose=False, exception=False, is_bootstrap=False, **kwargs):
     code = ret.wait()
     if code != 0:
         err = "failed to run: " + ' '.join(args)
+        if help_on_error is not None:
+            err = f"{err}\n{help_on_error}"
         if verbose or exception:
             raise RuntimeError(err)
         # For most failures, we definitely do want to print this error, or the user will have no
@@ -624,13 +627,22 @@ def _download_ci_llvm(self, llvm_sha, llvm_assertions):
         filename = "rust-dev-nightly-" + self.build + tarball_suffix
         tarball = os.path.join(rustc_cache, filename)
         if not os.path.exists(tarball):
+            help_on_error = "error: failed to download llvm from ci"
+            help_on_error += "\nhelp: old builds get deleted after a certain time"
+            help_on_error += "\nhelp: if trying to compile an old commit of rustc,"
+            help_on_error += " disable `download-ci-llvm` in config.toml:"
+            help_on_error += "\n"
+            help_on_error += "\n[llvm]"
+            help_on_error += "\ndownload-ci-llvm = false"
+            help_on_error += "\n"
             get(
                 base,
                 "{}/{}".format(url, filename),
                 tarball,
                 self.checksums_sha256,
                 verbose=self.verbose,
                 do_verify=False,
+                help_on_error=help_on_error,
             )
         unpack(tarball, tarball_suffix, self.llvm_root(),
                 match="rust-dev",