Rename Red Knot (#17820)

crates/ty_python_semantic/resources/mdtest/sys_platform.md

@@ -0,0 +1,58 @@
+# `sys.platform`
+
+## Explicit selection of `all` platforms
+
+When `python-platform="all"` is specified, we fall back to the type of `sys.platform` declared in
+typeshed:
+
+```toml
+[environment]
+python-platform = "all"
+```
+
+```py
+import sys
+
+reveal_type(sys.platform)  # revealed: LiteralString
+```
+
+## Explicit selection of a specific platform
+
+```toml
+[environment]
+python-platform = "linux"
+```
+
+```py
+import sys
+
+reveal_type(sys.platform)  # revealed: Literal["linux"]
+```
+
+## Testing for a specific platform
+
+```toml
+[environment]
+python-platform = "freebsd8"
+```
+
+### Exact comparison
+
+```py
+import sys
+
+reveal_type(sys.platform == "freebsd8")  # revealed: Literal[True]
+reveal_type(sys.platform == "linux")  # revealed: Literal[False]
+```
+
+### Substring comparison
+
+It is [recommended](https://docs.python.org/3/library/sys.html#sys.platform) to use
+`sys.platform.startswith(...)` for platform checks:
+
+```py
+import sys
+
+reveal_type(sys.platform.startswith("freebsd"))  # revealed: Literal[True]
+reveal_type(sys.platform.startswith("linux"))  # revealed: Literal[False]
+```