feat(ILO-399): modules — conditional imports via use ?<pred>

examples/conditional-imports-wasm.ilo

@@ -0,0 +1,19 @@
+-- Conditional imports example (ILO-399).
+-- Syntax: use ?<pred> "true-path" : "false-path"
+--
+-- Pick different modules at compile time based on the build target.
+-- Predicates: wasm (wasm32 target), native (host binary), test (ilo test run).
+--
+-- Example (not runnable inline — requires companion files):
+--   use ?wasm "platform/wasm-io.ilo" : "platform/native-io.ilo"
+--   use ?test "stubs/db-stub.ilo"    : "db/real-db.ilo"
+--
+-- The resolver evaluates the predicate against the current build target
+-- and imports exactly one of the two modules; the other is never read.
+-- Both branches follow the same import rules as unconditional `use`:
+-- flat import (all public declarations), selective import ([name1 name2]),
+-- or named-module alias (use alias: form) are NOT combined with ?<pred> —
+-- conditional imports always import all declarations from the chosen file.
+
+-- Standalone demonstration: a function that shows the active platform.
+platform>t;"native"

src/ast/mod.rs

@@ -92,6 +92,29 @@ pub struct Param {
     pub ty: Type,
 }
 
+/// Compile-time predicate for conditional `use` — `use ?wasm "a.ilo" : "b.ilo"`.
+///
+/// `wasm`   — true when building for wasm32 (`--target wasm`).
+/// `native` — true when building for a native host (`--target native`, default).
+/// `test`   — true when running under `ilo test` (`--target test`).
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize)]
+pub enum UsePredicate {
+    Wasm,
+    Native,
+    Test,
+}
+
+impl UsePredicate {
+    pub fn from_str(s: &str) -> Option<Self> {
+        match s {
+            "wasm" => Some(Self::Wasm),
+            "native" => Some(Self::Native),
+            "test" => Some(Self::Test),
+            _ => None,
+        }
+    }
+}
+
 /// Top-level declarations
 #[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
 pub enum Decl {
@@ -138,6 +161,9 @@ pub enum Decl {
     /// `use alias:"path/to/file.ilo"` — import all public declarations, prefixed
     ///   with `alias-` (e.g. `math-dbl`, `math-half`). Private (`_`-prefixed)
     ///   symbols are always excluded from named-module imports.
+    /// `use ?wasm "wasm-mod.ilo" : "native-mod.ilo"` — conditional import:
+    ///   import `path` when the predicate is true for the current build target,
+    ///   otherwise import `alt_path`. Resolved before verification.
     /// Resolved before verification; replaced by the imported declarations in
     /// the merged program. Stripped by the verifier/codegen as a safety net.
     Use {
@@ -147,6 +173,12 @@ pub enum Decl {
         /// Named module alias: `use alias:"path"` sets this to `Some("alias")`.
         /// When set, imported public symbols are renamed `alias-<name>`.
         alias: Option<String>,
+        /// Conditional form: `use ?<pred> "true-path" : "false-path"`.
+        /// When `Some`, `path` is the true-branch and `alt_path` is the
+        /// false-branch. `only` and `alias` are disallowed in this form.
+        predicate: Option<UsePredicate>,
+        /// The false-branch path for conditional imports. `None` for unconditional.
+        alt_path: Option<String>,
         #[serde(skip)]
         span: Span,
     },

src/codegen/explain.rs

@@ -551,6 +551,8 @@ mod tests {
             path: "x.ilo".into(),
             only: None,
             alias: None,
+            predicate: None,
+            alt_path: None,
             span: Span::UNKNOWN,
         });
         prog.declarations.push(Decl::Error {

src/codegen/fmt.rs

@@ -1298,6 +1298,8 @@ mod tests {
             path: "x.ilo".into(),
             only: None,
             alias: None,
+            predicate: None,
+            alt_path: None,
             span: Span::UNKNOWN,
         };
         let s = format_decl(&use_decl, FmtMode::Dense);

src/codegen/python.rs

@@ -2278,6 +2278,8 @@ mod tests {
             path: "x.ilo".into(),
             only: None,
             alias: None,
+            predicate: None,
+            alt_path: None,
             span: Span::UNKNOWN,
         });
         let py = emit(&prog);

src/interpreter/mod.rs

@@ -14370,6 +14370,8 @@ mod tests {
                 path: "x.ilo".to_string(),
                 only: None,
                 alias: None,
+                predicate: None,
+                alt_path: None,
                 span: Span { start: 0, end: 0 },
             },
         );