Import Resolution

This section specifies how an import path given to @import is resolved to a source file on disk, and how the set of loaded files is computed. The @import intrinsic's argument form and its error conditions are rules 4.13:79–4.13:89 in the intrinsics section.

Resolution Order

[10.2:1]

An import path P is resolved by trying the following interpretations in order; the first that matches is used:

If P is exactly "std", the import resolves to the standard library (see 10.2:6).
If P ends with the .rue extension, the import resolves to the file at exactly that relative path.
Otherwise, the import resolves to the file module {P}.rue, or, when no such file exists, to the directory-module facade {P}/_{basename}.rue (where basename is the final path component of P). If both exist, the import is ambiguous and rejected (rule 4.13:89).

[10.2:2]

Relative candidate paths are searched against base directories in order: first the directory containing the importing file, then the directory containing the root file (the first source file given to the compiler). A module found relative to the importing file takes precedence over a module at the same relative path found relative to the root file.

Transitive Loading

[10.2:3]

Importing a module loads it transitively: imports appearing in an imported file are themselves resolved and loaded, and so on, as if every reachable module had been listed on the command line. The importer of a transitively loaded file — not the root file — is the base for that file's own relative imports (per 10.2:2).

[10.2:4]

Each source file is loaded at most once per compilation. An import that resolves to an already-loaded file refers to that same module. Import cycles are therefore legal: two modules may import each other, and a chain of imports may return to its starting file.

[10.2:5]

Mutually importing modules:

// a.rue
const b = @import("b");
pub fn from_a() -> i32 { 1 }
pub fn a_uses_b() -> i32 { b.from_b() }

// b.rue
const a = @import("a");
pub fn from_b() -> i32 { 42 }

// main.rue
fn main() -> i32 {
    let a = @import("a");
    a.a_uses_b()  // 42
}

Standard Library Resolution

[10.2:6]

@import("std") resolves to the standard library facade _std.rue. It is searched for at $RUE_STD_PATH/_std.rue when the RUE_STD_PATH environment variable is set, and otherwise as an ordinary directory module std/_std.rue per 10.2:2. When both exist, $RUE_STD_PATH takes precedence. If no standard library is found, the import is a compile-time error (E0705).