Bazel: fix Rust deps patching for semver build metadata

Handle crate versions containing `+` build metadata (e.g., `0.9.11+spec-1.1.0`).
Bazel repo names use `-` instead of `+`, so the generated labels need patching
to reference the correct repo name.

Also adds documentation for both patching issues handled by patch_defs.py.

Author: github-actions[bot]

misc/bazel/3rdparty/patch_defs.py

@@ -2,15 +2,31 @@
 import re
 import pathlib
 
-label_re = re.compile(r'"@(vendor.*)//:(.+)-([\d.]+)"')
+# Problem number 1:
+# https://github.com/bazelbuild/rules_rust/issues/3255
+# `crates_vendor` generates broken labels in `defs.bzl`: instead of
+#     "anyhow": Label("@vendor__anyhow-1.0.44//:anyhow")
+# it produces
+#     "anyhow": Label("@vendor//:anyhow-1.0.44")
+# which results in: ERROR: no such package '@@[unknown repo 'vendor' requested from @@]//'
+#
+# Problem number 2:
+# Semver versions can contain `+` for build metadata (e.g., `0.9.11+spec-1.1.0`).
+# Bazel repo names use `-` instead of `+`, so `vendor_ts__toml-0.9.11+spec-1.1.0`
+# becomes `vendor_ts__toml-0.9.11-spec-1.1.0`. The generated labels reference the
+# `+` version which doesn't exist, causing:
+#     ERROR: no such package '@@[unknown repo 'vendor_ts__toml-0.9.11+spec-1.1.0'
+#     requested from @@ (did you mean 'vendor_ts__toml-0.9.11-spec-1.1.0'?)]//
+
+label_re = re.compile(r'"@(vendor.*)//:([^+]+)-([\d.]+(?:\+.*)?)"')
 
 file = pathlib.Path(sys.argv[1])
 temp = file.with_suffix(f'{file.suffix}.tmp')
 
 
 with open(file) as input, open(temp, "w") as output:
     for line in input:
-        line = label_re.sub(lambda m: f'"@{m[1]}__{m[2]}-{m[3]}//:{m[2].replace("-", "_")}"', line)
+        line = label_re.sub(lambda m: f'"@{m[1]}__{m[2]}-{m[3].replace("+", "-")}//:{m[2].replace("-", "_")}"', line)
         output.write(line)
 
 temp.rename(file)