184c5ab180
delay expand macro bang when there has indeterminate path Related #98291 I will attempt to clarify the root problem through several examples: Firstly, ```rs // rustc code.rs --edition=2018 macro_rules! wrap { () => { macro_rules! _a { () => { "Hello world" }; } }; } wrap!(); use _a as a; fn main() { format_args!(_a!()); } ``` The above case will compile successfully because `_a` is defined after the `wrap` expaned, ensuring `_a` can be resolved without any issues. And, ```rs // rustc code.rs --edition=2018 macro_rules! wrap { () => { macro_rules! _a { () => { "Hello world" }; } }; } wrap!(); use _a as a; fn main() { format_args!("{}", a!()); } ``` The above example will also compile successfully because the `parse_args` in `expand_format_args_impl` will return a value `MacroInput { fmtstr: Expr::Lit::Str, args: [Expr::MacroCall]}`. Since the graph for `args` will be build lately, `a` will eventually be resolved. However, in the case of: ```rs // rustc code.rs --edition=2018 macro_rules! wrap { () => { macro_rules! _a { () => { "Hello world" }; } }; } wrap!(); use _a as a; fn main() { format_args!(a!()); } ``` The result of `parse_args` is `MacroInput {fmtstr: Expr::Lit::Macro, args: [] }`, we attempt to expand `fmtstr` **eagerly** within `expr_to_spanned_string`. Although we have recorded `(root, _a)` into resolutions, `use _a as a` is an indeterminate import, which will not try to resolve under the conditions of `expander.monotonic = false`. Therefore, I've altered the strategy for resolving indeterminate imports, ensuring it will also resolve during eager expansion. This could be a significant change to the resolution infra. However, I think it's acceptable if the goal of avoiding resolution under eager expansion is to save time. r? `@petrochenkov` |
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The Rust Programming Language
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