add upgrade guide

Author: adriangb

docs/source/library-user-guide/upgrading.md

@@ -451,6 +451,109 @@ Instead of silently succeeding.
 
 The remove API no longer requires a mutable instance
 
+### `SimplifyInfo` trait removed, `SimplifyContext` now uses builder-style API
+
+The `SimplifyInfo` trait has been removed and replaced with the concrete `SimplifyContext` struct. This simplifies the expression simplification API and removes the need for trait objects.
+
+**Who is affected:**
+
+- Users who implemented custom `SimplifyInfo` implementations
+- Users who implemented `ScalarUDFImpl::simplify()` for custom scalar functions
+- Users who directly use `SimplifyContext` or `ExprSimplifier`
+
+**Breaking changes:**
+
+1. The `SimplifyInfo` trait has been removed entirely
+2. `SimplifyContext` no longer takes `&ExecutionProps` - it now uses a builder-style API with direct fields
+3. `ScalarUDFImpl::simplify()` now takes `&SimplifyContext` instead of `&dyn SimplifyInfo`
+4. Time-dependent function simplification (e.g., `now()`) is now optional - if `query_execution_start_time` is `None`, these functions won't be simplified
+
+**Migration guide:**
+
+If you implemented a custom `SimplifyInfo`:
+
+**Before:**
+
+```rust,ignore
+impl SimplifyInfo for MySimplifyInfo {
+    fn is_boolean_type(&self, expr: &Expr) -> Result<bool> { ... }
+    fn nullable(&self, expr: &Expr) -> Result<bool> { ... }
+    fn execution_props(&self) -> &ExecutionProps { ... }
+    fn get_data_type(&self, expr: &Expr) -> Result<DataType> { ... }
+}
+```
+
+**After:**
+
+Use `SimplifyContext` directly with the builder-style API:
+
+```rust,ignore
+let context = SimplifyContext::default()
+    .with_schema(schema)
+    .with_config_options(config_options)
+    .with_query_execution_start_time(Some(Utc::now())); // or use .with_current_time()
+```
+
+If you implemented `ScalarUDFImpl::simplify()`:
+
+**Before:**
+
+```rust,ignore
+fn simplify(
+    &self,
+    args: Vec<Expr>,
+    info: &dyn SimplifyInfo,
+) -> Result<ExprSimplifyResult> {
+    let now_ts = info.execution_props().query_execution_start_time;
+    // ...
+}
+```
+
+**After:**
+
+```rust,ignore
+fn simplify(
+    &self,
+    args: Vec<Expr>,
+    info: &SimplifyContext,
+) -> Result<ExprSimplifyResult> {
+    // query_execution_start_time is now Option<DateTime<Utc>>
+    // Return Original if time is not set (simplification skipped)
+    let Some(now_ts) = info.query_execution_start_time() else {
+        return Ok(ExprSimplifyResult::Original(args));
+    };
+    // ...
+}
+```
+
+If you created `SimplifyContext` from `ExecutionProps`:
+
+**Before:**
+
+```rust,ignore
+let props = ExecutionProps::new();
+let context = SimplifyContext::new(&props).with_schema(schema);
+```
+
+**After:**
+
+```rust,ignore
+let context = SimplifyContext::default()
+    .with_schema(schema)
+    .with_config_options(config_options)
+    .with_current_time(); // Sets query_execution_start_time to Utc::now()
+```
+
+**Available `SimplifyContext` methods:**
+
+- `with_schema(DFSchemaRef)` - Set the schema for type resolution
+- `with_config_options(Arc<ConfigOptions>)` - Set configuration options
+- `with_query_execution_start_time(Option<DateTime<Utc>>)` - Set query start time for time-dependent simplification
+- `with_current_time()` - Convenience method to set query start time to `Utc::now()`
+- `schema()` - Get the schema
+- `query_execution_start_time()` - Get the query start time (returns `Option<DateTime<Utc>>`)
+- `config_options()` - Get the configuration options
+
 ### FFI crate updates
 
 Many of the structs in the `datafusion-ffi` crate have been updated to allow easier