fix(formatter): preserve by and semicolon for bare genai ability declarations

docs/docs/community/release_notes/unreleased/jaclang/5607.bugfix.md

@@ -0,0 +1 @@
+- **Formatter: Bare GenAI Ability `by` and Semicolon Preservation**: The Jac formatter no longer strips the `by` keyword and trailing semicolon from bare genai ability declarations (e.g. `def classify(s: str) -> str by llm;`). Previously, formatting such a declaration would silently drop `by <model>;`, producing invalid output. The fix inspects child tokens of the `Name` node in `DocIRGenPass.exit_name` and correctly renders the full `by <name>;` fragment when present. Formatting is also idempotent.

jac/jaclang/compiler/passes/tool/impl/doc_ir_gen_pass.impl.jac

@@ -284,10 +284,37 @@ impl DocIRGenPass.exit_int(nd: uni.Int) -> None {
 
 """Generate DocIR for names."""
 impl DocIRGenPass.exit_name(nd: uni.Name) -> None {
-    if nd.is_kwesc {
-        nd.gen.doc_ir = self.text(f"`{nd.value}", source_token=nd);
+    name_text = f"`{nd.value}" if nd.is_kwesc else nd.value;
+    by_kid = next(
+        (
+            k
+            for k in nd.kid
+            if isinstance(k, uni.Token) and k.name == Tok.KW_BY
+        ),
+        None
+    );
+    if by_kid is not None {
+        # Bare genai body (`by <name>;`): the parser attaches `by` and `;`
+        # as kids of this Name node. Render them so they are not lost.
+        semi_kid = next(
+            (
+                k
+                for k in nd.kid
+                if isinstance(k, uni.Semi)
+            ),
+            None
+        );
+        parts: list[doc.DocType] = [
+            by_kid.gen.doc_ir,
+            self.space(),
+            self.text(name_text, source_token=nd)
+        ];
+        if semi_kid is not None {
+            parts.append(semi_kid.gen.doc_ir);
+        }
+        nd.gen.doc_ir = self.concat(parts, ast_node=nd);
     } else {
-        nd.gen.doc_ir = self.text(nd.value, source_token=nd);
+        nd.gen.doc_ir = self.text(name_text, source_token=nd);
     }
 }
 

jac/tests/compiler/passes/tool/test_jac_format_pass.jac

@@ -518,6 +518,27 @@ test "jsx attributes and children group independently" {
     );
 }
 
+"""Regression: formatter must preserve `by <name>;` (bare genai ability
+without parentheses) — previously both `by` and `;` were stripped."""
+test "genai ability bare name preserves by and semicolon" {
+    source = "def classify(s: str) -> str by llm;\n";
+    prog = JacProgram.jac_str_formatter(source_str=source, file_path="<test>.jac");
+    assert not prog.errors_had , f"formatter errors: {prog.errors_had}";
+    formatted = prog.mod.main.gen.jac;
+    assert "by" in formatted , (
+        f"`by` keyword was stripped from genai ability:\n{repr(formatted)}"
+    );
+    assert formatted.rstrip().endswith(";") , (
+        f"semicolon was stripped from genai ability:\n{repr(formatted)}"
+    );
+    assert "by llm;" in formatted , (
+        f"expected `by llm;` in formatted output, got:\n{repr(formatted)}"
+    );
+    # Idempotency
+    prog2 = JacProgram.jac_str_formatter(source_str=formatted, file_path="<test>.jac");
+    assert formatted == prog2.mod.main.gen.jac , "genai bare-name formatting is not idempotent";
+}
+
 """Regression: jac_str_formatter must populate errors_had on syntax error
 so that the LSP returns the original source instead of an empty string."""
 test "syntax error preserves original source" {
@@ -533,7 +554,6 @@ test "syntax error preserves original source" {
     # return formatted if no errors, else return original source
     result = gen_output if not prog.errors_had else bad_source;
     assert result == bad_source , (
-        "Formatter must return original source on syntax error, "
-        f"got: {repr(result)}"
+        "Formatter must return original source on syntax error, " f"got: {repr(result)}"
     );
 }