fix(remap): Preserve type defs when assigning fields (#7118)

* fix(remap): Preserve type defs when assigning fields

Previously, remap would overwrite the type def of `.` whenever a new
field was assigned. That is:

```
.foo = 5
.bar = 6
```

Would result in the compiler only having type info for `.bar`.

This change causes it to merge the typedefs whenever a list of path
segments appears.

Signed-off-by: Jesse Szwedko <[email protected]>

docs/reference/remap.cue

@@ -104,7 +104,7 @@ remap: #Remap & {
 				.tid = to_int!(.tid)
 
 				# Extract structured data
-				message_parts = split(.message, ", ", limit: 2) ?? []
+				message_parts = split(.message, ", ", limit: 2)
 				structured = parse_key_value(message_parts[1], key_value_delimiter: ":", field_delimiter: ",") ?? {}
 				.message = message_parts[0]
 				. = merge(., structured)

lib/vrl/compiler/src/expression/assignment.rs

@@ -197,18 +197,12 @@ impl Target {
             new_type_def: TypeDef,
             path: &Option<Path>,
         ) -> TypeDef {
-            // If the assignment is into a specific index, we want to keep the
-            // existing type def, and only update the type def at the provided
-            // index.
-            let is_index_assignment = path
-                .as_ref()
-                .and_then(|p| p.segments().last().map(|s| s.is_index()))
-                .unwrap_or_default();
-
-            if is_index_assignment {
-                current_type_def.clone().merge_overwrite(new_type_def)
-            } else {
+            // If the assignment is onto root or has no path (root variable assignment), use the
+            // new type def, otherwise merge the type defs.
+            if path.as_ref().map(|path| path.is_root()).unwrap_or(true) {
                 new_type_def
+            } else {
+                current_type_def.clone().merge_overwrite(new_type_def)
             }
         }
 

lib/vrl/tests/tests/issues/6792_lost_type_defs.vrl

@@ -0,0 +1,7 @@
+# https://github.com/timberio/vector/issues/6792#issuecomment-817986771
+# result: {"field1": "2020-01-01T00:00:00Z", "field2": 1577836800, "timestamp": "2020-01-01T00:00:00+00:00"}
+
+.timestamp = "2020-01-01T00:00:00+00:00"
+.field1 = parse_timestamp!(.timestamp, format: "%+")
+.field2 = to_int(.field1)
+.