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docs: add stdlib env::var(_os) panic #63461

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Aug 12, 2019
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docs: add stdlib env::var(_os) panic #63461

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12 changes: 12 additions & 0 deletions src/libstd/env.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -182,6 +182,12 @@ impl fmt::Debug for VarsOs {
/// * Environment variable is not present
/// * Environment variable is not valid unicode
///
/// # Panics
///
/// This function may panic if `key` is empty, contains an ASCII equals sign
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Is it "may panic" or "panics" (definitive)?

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The function relies on std::sys::os, so the behaviour differs by operating system. We could update the docs to make this clearer.

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Hmm, I'm not sure what is the practice in this case. Maybe "may" is fine.

BTW, I do wonder why this behavior was chosen, that if key contains a nul then it panics. It makes sense for setting a var, but when getting, it makes more sense to me that it just return None. The code comment in the unix implementation seems to agree, I think..

rust/src/libstd/sys/unix/os.rs

Lines 469 to 471 in ad7c55e

// environment variables with a nul byte can't be set, so their value is
// always None as well
let k = CString::new(k.as_bytes())?;

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Another question: the function documentation says that when key is not present, an error is returned, not a panic. So is the "is empty" here correct?

/// `'='` or the NUL character `'\0'`, or when the value contains the NUL
/// character.
///
/// # Examples
///
/// ```
Expand Down Expand Up @@ -210,6 +216,12 @@ fn _var(key: &OsStr) -> Result<String, VarError> {
///
/// [`None`]: ../option/enum.Option.html#variant.None
///
/// # 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.
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NUL character is repeated twice in both of these?

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This is copied verbatim from the underlying functions called, which state they may crash when either the key or the value contain a null byte.

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Oh, I missed the key/value distinction.

///
/// # Examples
///
/// ```
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