bjoernager/rust
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Explain compile-time vs run-time difference in env!() error message

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This commit is contained in:
Kornel 2023-02-28 16:20:43 +00:00
parent 31f858d9a5
commit 2407b0c578
5 changed files with 43 additions and 20 deletions
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40
compiler/rustc_builtin_macros/src/env.rs
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@ -53,7 +53,7 @@ pub fn expand_env<'cx>(
tts: TokenStream,
) -> Box<dyn base::MacResult + 'cx> {
let mut exprs = match get_exprs_from_tts(cx, tts) {
Some(exprs) if exprs.is_empty() => {
Some(exprs) if exprs.is_empty() || exprs.len() > 2 => {
cx.span_err(sp, "env! takes 1 or 2 arguments");
return DummyResult::any(sp);
}
@ -64,28 +64,48 @@ pub fn expand_env<'cx>(
let Some((var, _style)) = expr_to_string(cx, exprs.next().unwrap(), "expected string literal") else {
return DummyResult::any(sp);
};
let msg = match exprs.next() {
None => Symbol::intern(&format!("environment variable `{}` not defined", var)),
let custom_msg = match exprs.next() {
None => None,
Some(second) => match expr_to_string(cx, second, "expected string literal") {
None => return DummyResult::any(sp),
Some((s, _style)) => s,
Some((s, _style)) => Some(s),
},
};
if exprs.next().is_some() {
cx.span_err(sp, "env! takes 1 or 2 arguments");
return DummyResult::any(sp);
}
let sp = cx.with_def_site_ctxt(sp);
let value = env::var(var.as_str()).ok().as_deref().map(Symbol::intern);
cx.sess.parse_sess.env_depinfo.borrow_mut().insert((var, value));
let e = match value {
None => {
cx.span_err(sp, msg.as_str());
let (msg, help) = match custom_msg {
None => (
format!("environment variable `{var}` not defined at compile time"),
Some(help_for_missing_env_var(var.as_str())),
),
Some(s) => (s.to_string(), None),
};
let mut diag = cx.struct_span_err(sp, &msg);
if let Some(help) = help {
diag.help(help);
}
diag.emit();
return DummyResult::any(sp);
}
Some(value) => cx.expr_str(sp, value),
};
MacEager::expr(e)
}
fn help_for_missing_env_var(var: &str) -> String {
if var.starts_with("CARGO_")
|| var.starts_with("DEP_")
|| matches!(var, "OUT_DIR" | "OPT_LEVEL" | "PROFILE" | "HOST" | "TARGET")
{
format!(
"Cargo sets build script variables at run time. Use `std::env::var(\"{var}\")` instead"
)
} else {
format!("Use `std::env::var(\"{var}\")` to read the variable at run time")
}
}