docs: update READMEs with new APIs and usage examples

packages/plpgsql-deparser/README.md

@@ -175,6 +175,50 @@ interface PLpgSQLDeparserOptions {
 }
 ```
 
+## Return Context
+
+For correct `RETURN` statement handling, you can pass return type information:
+
+```typescript
+import { deparseSync, ReturnInfo } from 'plpgsql-deparser';
+
+// Without return info, the deparser uses conservative defaults
+const body1 = deparseSync(parseResult);
+
+// With return info, the deparser emits correct RETURN vs RETURN NULL
+const returnInfo: ReturnInfo = { kind: 'setof' };
+const body2 = deparseSync(parseResult, {}, returnInfo);
+```
+
+Supported return kinds: `'void'`, `'scalar'`, `'setof'`, `'trigger'`, `'out_params'`
+
+## Hydration Utilities
+
+The deparser includes utilities for working with "hydrated" PL/pgSQL ASTs, where embedded SQL expressions are parsed into SQL AST nodes for transformation.
+
+```typescript
+import { 
+  hydratePlpgsqlAst, 
+  dehydratePlpgsqlAst,
+  isHydratedExpr,
+  getOriginalQuery 
+} from 'plpgsql-deparser';
+
+// Hydrate: convert PLpgSQL_expr.query strings into SQL AST nodes
+const hydrated = hydratePlpgsqlAst(plpgsqlFunction);
+
+// Now you can traverse and modify embedded SQL expressions as AST nodes
+// (e.g., rename schemas, rewrite table references)
+
+// Dehydrate: convert SQL AST nodes back to query strings
+const dehydrated = dehydratePlpgsqlAst(hydrated);
+
+// Then deparse to get the final function body
+const body = deparseFunctionSync(dehydrated);
+```
+
+The `isHydratedExpr()` helper checks if an expression has been hydrated, and `getOriginalQuery()` retrieves the original query string from a hydrated expression.
+
 ## Note on AST Structure
 
 The PL/pgSQL AST returned by `parsePlPgSQL` represents the internal structure of function bodies, not the `CREATE FUNCTION` statement itself. To get a complete function definition, you would need to:

packages/plpgsql-parser/README.md

@@ -191,6 +191,78 @@ class PLpgSQLNodePath<TTag extends string = string> {
 }
 ```
 
+## Return Type Helpers
+
+Extract return type information from `CreateFunctionStmt` for correct RETURN statement handling:
+
+```typescript
+import { parse, getReturnInfoFromParsedFunction, loadModule } from 'plpgsql-parser';
+
+await loadModule();
+
+const parsed = parse(`
+  CREATE FUNCTION get_users() RETURNS SETOF users LANGUAGE plpgsql AS $$
+  BEGIN
+    RETURN QUERY SELECT * FROM users;
+    RETURN;
+  END;
+  $$;
+`);
+
+const returnInfo = getReturnInfoFromParsedFunction(parsed.functions[0]);
+console.log(returnInfo.kind); // 'setof'
+```
+
+The helper detects: `'void'`, `'scalar'`, `'setof'`, `'trigger'`, `'out_params'`
+
+## Schema Rename Example
+
+Transform schema names across both SQL and embedded PL/pgSQL expressions:
+
+```typescript
+import { parse, walk, walkParsedScript, deparseSync, loadModule } from 'plpgsql-parser';
+import { walk as walkSql } from '@pgsql/traverse';
+
+await loadModule();
+
+const schemaMap = { app_public: 'myapp_v2', app_private: 'myapp_internal' };
+
+function renameSchema(node: any) {
+  if (node.schemaname && schemaMap[node.schemaname]) {
+    node.schemaname = schemaMap[node.schemaname];
+  }
+}
+
+const parsed = parse(`
+  CREATE FUNCTION app_public.get_user(p_id int)
+  RETURNS app_public.users
+  LANGUAGE plpgsql AS $$
+  BEGIN
+    RETURN (SELECT * FROM app_public.users WHERE id = p_id);
+  END;
+  $$;
+`);
+
+// Rename schemas in outer SQL AST (function name, return type)
+walkSql(parsed.sql, {
+  RangeVar: (path) => renameSchema(path.node),
+  TypeName: (path) => {
+    const names = path.node.names;
+    if (names?.[0]?.String?.sval && schemaMap[names[0].String.sval]) {
+      names[0].String.sval = schemaMap[names[0].String.sval];
+    }
+  },
+});
+
+// Rename schemas in PL/pgSQL embedded SQL (SELECT, INSERT, etc.)
+walkParsedScript(parsed, {}, {
+  RangeVar: (path) => renameSchema(path.node),
+});
+
+const output = deparseSync(parsed);
+// All app_public references are now myapp_v2
+```
+
 ## Re-exports
 
 For power users, the package re-exports underlying primitives:
@@ -201,6 +273,8 @@ For power users, the package re-exports underlying primitives:
 - `deparsePlpgsqlBody` - PL/pgSQL deparser from `plpgsql-deparser`
 - `hydratePlpgsqlAst` - Hydration utility from `plpgsql-deparser`
 - `dehydratePlpgsqlAst` - Dehydration utility from `plpgsql-deparser`
+- `getReturnInfo` - Extract return type from `CreateFunctionStmt`
+- `ReturnInfo`, `ReturnInfoKind` - Return type info types
 
 ## License