Auto merge of #29298 - tbu-:pr_doc_env_panic, r=alexcrichton

Author: bors

src/libstd/env.rs

@@ -260,6 +260,12 @@ impl Error for VarError {
 ///  - [Austin Group Bugzilla](http://austingroupbugs.net/view.php?id=188)
 ///  - [GNU C library Bugzilla](https://sourceware.org/bugzilla/show_bug.cgi?id=15607#c2)
 ///
+/// # Panics
+///
+/// This function may panic if `key` is empty, contains an ASCII equals sign
+/// `'='` or the NUL character `'\0'`, or when the value contains the NUL
+/// character.
+///
 /// # Examples
 ///
 /// ```
@@ -292,6 +298,12 @@ fn _set_var(k: &OsStr, v: &OsStr) {
 ///  - [Austin Group Bugzilla](http://austingroupbugs.net/view.php?id=188)
 ///  - [GNU C library Bugzilla](https://sourceware.org/bugzilla/show_bug.cgi?id=15607#c2)
 ///
+/// # Panics
+///
+/// This function may panic if `key` is empty, contains an ASCII equals sign
+/// `'='` or the NUL character `'\0'`, or when the value contains the NUL
+/// character.
+///
 /// # Examples
 ///
 /// ```