Add imports functionality

CHANGELOG.md

@@ -1,3 +1,7 @@
+# Unreleased
+
+* Replaced the deprecated `WithFile` trait with `WithContent` and `WithSource` to cleanly separate single-file execution from multi-file environments. Additionally, replaced the `file()` method on `RichError` with `source()`. [#266](https://github.com/BlockstreamResearch/SimplicityHL/pull/266)
+
 # 0.5.0-rc.0 - 2026-03-14
 
 * Migrate from the `pest` parser to a new `chumsky`-based parser, improving parser recovery and enabling multiple parse errors to be reported in one pass [#185](https://github.com/BlockstreamResearch/SimplicityHL/pull/185)

doc/architecture.md

@@ -0,0 +1,7 @@
+# Architecture Note: Omitted Keywords
+The `crate` and `super` keywords were not added to the compiler because they
+are unnecessary at this stage. Typically, they are used to resolve relative
+paths during import parsing. However, in our architecture, the prefix before
+the first `::` in a `use` statement is always an dependency root path. Since all
+dependency root paths are unique and strictly bound to specific paths, the resolver
+can always unambiguously resolve the path without needing relative pointers.

fuzz/fuzz_targets/compile_parse_tree.rs

@@ -4,7 +4,7 @@
 fn do_test(data: &[u8]) {
     use arbitrary::Arbitrary;
 
-    use simplicityhl::error::WithFile;
+    use simplicityhl::error::WithContent;
     use simplicityhl::{ast, named, parse, ArbitraryOfType, Arguments};
 
     let mut u = arbitrary::Unstructured::new(data);
@@ -22,7 +22,7 @@ fn do_test(data: &[u8]) {
     };
     let simplicity_named_construct = ast_program
         .compile(arguments, false)
-        .with_file("")
+        .with_content("")
         .expect("AST should compile with given arguments");
     let _simplicity_commit = named::forget_names(&simplicity_named_construct);
 }

src/ast.rs

@@ -762,6 +762,10 @@ impl AbstractSyntaxTree for Item {
             parse::Item::Function(function) => {
                 Function::analyze(function, ty, scope).map(Self::Function)
             }
+            parse::Item::Use(use_decl) => Err(RichError::new(
+                Error::CannotCompile("The `use` keyword is not supported yet.".to_string()),
+                *use_decl.span(),
+            )),
             parse::Item::Module => Ok(Self::Module),
         }
     }