Raise Zig unsupported expression diagnostics

Author: code5717

CHANGELOG.md

@@ -44,6 +44,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   - Local file-based imports now load dependencies during semantic analysis and fail closed on missing or broken modules.
   - Built-in stdlib imports such as `std/io` and `std/math` remain virtual so existing examples do not require on-disk stdlib `.a7` files.
 
+- **Zig backend diagnostics**
+  - Unsupported expression nodes now raise compiler-side `CodegenError` instead of emitting Zig `@compileError` fallback expressions.
+
 - **Semantic and preprocessing correctness**
   - `defer` now traverses its parsed `statement` payload in both type checking and semantic validation.
   - `ret` semantic validation now traverses the parser's `value` payload.

MISSING_FEATURES.md

@@ -29,6 +29,7 @@
 15. Debug/release example artifact verification is available through `scripts/build_examples.py`.
 16. `run_all_tests.sh` includes C backend verification, both example E2E verifiers, debug/release artifact builds, the error-stage matrix, docs style checks, and full pytest.
 17. Local file-based imports now fail closed during semantic analysis instead of swallowing module loading failures.
+18. Zig unsupported expression fallbacks now fail as compiler-side codegen errors instead of generated `@compileError` expressions.
 
 ---
 

RELEASE_READINESS_REVIEW.md

@@ -60,9 +60,8 @@ not factually provable from local tests alone.
 
 ## Recommended Next Pass
 
-1. Replace Zig backend `@compileError("unsupported")` fallbacks with compiler
-   codegen errors.
-2. Add tag-based release workflow after choosing the package publishing target.
-3. Add secret scanning to CI.
-4. Expand differential backend tests beyond examples.
-5. Unify virtual stdlib imports with file-based module semantics.
+1. Add tag-based release workflow after choosing the package publishing target.
+2. Add secret scanning to CI.
+3. Expand differential backend tests beyond examples.
+4. Unify virtual stdlib imports with file-based module semantics.
+5. Implement `fall` semantic validation and backend lowering.

TODO.md

@@ -21,9 +21,9 @@ These are bugs and schema mismatches in already-implemented features.
   Files: `src/passes/semantic_validator.py`, `src/backends/zig.py`, `src/backends/c.py`
   Notes: `NodeKind.FALL` is parsed and documented, but semantic validation and backend lowering are still pending.
 
-- [ ] Replace Zig backend `@compileError("unsupported: ...")` fallbacks with compiler-side codegen errors.
+- [x] Replace Zig backend `@compileError("unsupported: ...")` fallbacks with compiler-side codegen errors.
   Files: `src/backends/zig.py`
-  Notes: unsupported AST nodes should fail during compilation, not after emitting Zig source.
+  Notes: unsupported expression nodes now raise `CodegenError` during A7 compilation.
 
 - [ ] Stop C slice/iteration lowering from re-evaluating side-effectful expressions.
   Files: `src/backends/c.py`

src/backends/zig.py

@@ -1015,7 +1015,7 @@ def _emit_expr(self, node: ASTNode) -> str:
                       NodeKind.TYPE_GENERIC):
             return self._emit_type_node(node)
         else:
-            return f"@compileError(\"unsupported: {kind.name}\")"
+            raise CodegenError(f"Zig backend: unsupported expression node '{kind.name}'", node.span)
 
     def _emit_literal(self, node: ASTNode) -> str:
         """Emit a literal value."""

test/test_codegen_zig.py

@@ -21,7 +21,9 @@
 from src.compile import A7Compiler
 from src.tokens import Tokenizer
 from src.parser import Parser
+from src.ast_nodes import ASTNode, NodeKind
 from src.backends.zig import ZigCodeGenerator
+from src.errors import CodegenError
 from src.passes import NameResolutionPass, TypeCheckingPass, SemanticValidationPass
 
 EXAMPLES_DIR = PROJECT_ROOT / "examples"
@@ -178,6 +180,12 @@ def test_ast_check(self, example, tmp_path):
 class TestCodePatterns:
     """Test that specific A7 constructs produce expected Zig patterns."""
 
+    def test_unsupported_expression_raises_codegen_error(self):
+        codegen = ZigCodeGenerator()
+
+        with pytest.raises(CodegenError, match="unsupported expression node 'FALL'"):
+            codegen._emit_expr(ASTNode(NodeKind.FALL))
+
     def test_hello_world(self):
         source = '''
 io :: import "std/io"