Recast the PYDANTIC_ERRORS_INCLUDE_URL environment variable and doc…

…ument it

Refs pydantic#1118 (comment)

python/pydantic_core/_pydantic_core.pyi

@@ -787,6 +787,18 @@ class ValidationError(ValueError):
             a JSON string.
         """
 
+    def __repr__(self) -> str:
+        """
+        A string representation of the validation error.
+
+        Whether or not documentation URLs are included in the repr is controlled by the
+        environment variable `PYDANTIC_ERRORS_INCLUDE_URL` being set to `1` or
+        `true`; by default, URLs are shown.
+
+        Due to implementation details, this environment variable can only be set once,
+        before the first validation error is created.
+        """
+
 @final
 class PydanticCustomError(ValueError):
     def __new__(

src/errors/validation_exception.rs

@@ -194,8 +194,8 @@ impl ValidationError {
 static URL_ENV_VAR: GILOnceCell<bool> = GILOnceCell::new();
 
 fn _get_include_url_env() -> bool {
-    match std::env::var("PYDANTIC_ERRORS_OMIT_URL") {
-        Ok(val) => val.is_empty(),
+    match std::env::var("PYDANTIC_ERRORS_INCLUDE_URL") {
+        Ok(val) => val == "1" || val.to_lowercase() == "true",
         Err(_) => true,
     }
 }