Add projection v1.2.0 to the list of schema URIs in projection.py (#1590)

* Add projection v1.2.0 to the list schema URIs in projection.py

The migration of projection to latest version systematically pops the field epsg. If extension URI is pointing to versions 1.0.0 or 1.1.0, it is also changed to point to version 2.0.0. 
However, if schema URI is v1.2.0 the extension schema URI is not changed. I propose to change it as well in that case so that the change is explicit for all versions < 2.0.0. That would help finding out that a change occurred.

* Add test, migration for proj v1.2.0

---------

Co-authored-by: Julia Signell <[email protected]>

Author: floriandeboissieu

pystac/extensions/projection.py

@@ -30,6 +30,7 @@
 SCHEMA_URIS: list[str] = [
     "https://stac-extensions.github.io/projection/v1.0.0/schema.json",
     "https://stac-extensions.github.io/projection/v1.1.0/schema.json",
+    "https://stac-extensions.github.io/projection/v1.2.0/schema.json",
     SCHEMA_URI,
 ]
 PREFIX: str = "proj:"
@@ -467,6 +468,7 @@ class ProjectionExtensionHooks(ExtensionHooks):
         "projection",
         "https://stac-extensions.github.io/projection/v1.0.0/schema.json",
         "https://stac-extensions.github.io/projection/v1.1.0/schema.json",
+        "https://stac-extensions.github.io/projection/v1.2.0/schema.json",
     }
     stac_object_types = {pystac.STACObjectType.ITEM}
 
@@ -478,12 +480,27 @@ def migrate(
 
         # proj:epsg moved to proj:code
         if epsg := obj["properties"].pop("proj:epsg", None):
-            obj["properties"]["proj:code"] = f"EPSG:{epsg}"
+            if obj["properties"].get("proj:code", None) is None:
+                obj["properties"]["proj:code"] = f"EPSG:{epsg}"
+            elif not obj["properties"]["proj:code"] == f"EPSG:{epsg}":
+                warnings.warn(
+                    "Both proj:code and proj:epsg are specified and they have "
+                    "conflicting values. This might lead to surprising behavior.",
+                    UserWarning,
+                )
 
         for key in ["assets", "item_assets"]:
             for asset in obj.get(key, {}).values():
                 if epsg := asset.pop("proj:epsg", None):
-                    asset["proj:code"] = f"EPSG:{epsg}"
+                    if asset.get("proj:code", None) is None:
+                        asset["proj:code"] = f"EPSG:{epsg}"
+                    elif not asset["proj:code"] == f"EPSG:{epsg}":
+                        warnings.warn(
+                            "Both proj:code and proj:epsg are specified and they "
+                            "have conflicting values. This might lead to surprising "
+                            "behavior.",
+                            UserWarning,
+                        )
 
         super().migrate(obj, version, info)