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new 78433a7927 fix: document and fix macro hygiene for `config_field!`
(#16473)
78433a7927 is described below
commit 78433a7927b531996057ad2a9224d115b637cd6f
Author: Marco Neumann <ma...@crepererum.net>
AuthorDate: Mon Jun 23 12:36:27 2025 +0200
fix: document and fix macro hygiene for `config_field!` (#16473)
---
datafusion/common/src/config.rs | 41 +++++++++++++++++++++++++-----
datafusion/core/tests/macro_hygiene/mod.rs | 37 +++++++++++++++++++++++++++
2 files changed, 72 insertions(+), 6 deletions(-)
diff --git a/datafusion/common/src/config.rs b/datafusion/common/src/config.rs
index f16e30969b..ac3f908e37 100644
--- a/datafusion/common/src/config.rs
+++ b/datafusion/common/src/config.rs
@@ -1248,7 +1248,10 @@ impl<F: ConfigField + Default> ConfigField for Option<F>
{
}
}
-fn default_transform<T>(input: &str) -> Result<T>
+/// Default transformation to parse a [`ConfigField`] for a string.
+///
+/// This uses [`FromStr`] to parse the data.
+pub fn default_config_transform<T>(input: &str) -> Result<T>
where
T: FromStr,
<T as FromStr>::Err: Sync + Send + Error + 'static,
@@ -1265,19 +1268,45 @@ where
})
}
+/// Macro that generates [`ConfigField`] for a given type.
+///
+/// # Usage
+/// This always requires [`Display`] to be implemented for the given type.
+///
+/// There are two ways to invoke this macro. The first one uses
+/// [`default_config_transform`]/[`FromStr`] to parse the data:
+///
+/// ```ignore
+/// config_field(MyType);
+/// ```
+///
+/// Note that the parsing error MUST implement [`std::error::Error`]!
+///
+/// Or you can specify how you want to parse an [`str`] into the type:
+///
+/// ```ignore
+/// fn parse_it(s: &str) -> Result<MyType> {
+/// ...
+/// }
+///
+/// config_field(
+/// MyType,
+/// value => parse_it(value)
+/// );
+/// ```
#[macro_export]
macro_rules! config_field {
($t:ty) => {
- config_field!($t, value => default_transform(value)?);
+ config_field!($t, value =>
$crate::config::default_config_transform(value)?);
};
($t:ty, $arg:ident => $transform:expr) => {
- impl ConfigField for $t {
- fn visit<V: Visit>(&self, v: &mut V, key: &str, description:
&'static str) {
+ impl $crate::config::ConfigField for $t {
+ fn visit<V: $crate::config::Visit>(&self, v: &mut V, key: &str,
description: &'static str) {
v.some(key, self, description)
}
- fn set(&mut self, _: &str, $arg: &str) -> Result<()> {
+ fn set(&mut self, _: &str, $arg: &str) ->
$crate::error::Result<()> {
*self = $transform;
Ok(())
}
@@ -1286,7 +1315,7 @@ macro_rules! config_field {
}
config_field!(String);
-config_field!(bool, value =>
default_transform(value.to_lowercase().as_str())?);
+config_field!(bool, value =>
default_config_transform(value.to_lowercase().as_str())?);
config_field!(usize);
config_field!(f64);
config_field!(u64);
diff --git a/datafusion/core/tests/macro_hygiene/mod.rs
b/datafusion/core/tests/macro_hygiene/mod.rs
index 9196efec97..e5396ce219 100644
--- a/datafusion/core/tests/macro_hygiene/mod.rs
+++ b/datafusion/core/tests/macro_hygiene/mod.rs
@@ -65,3 +65,40 @@ mod config_namespace {
}
}
}
+
+mod config_field {
+ // NO other imports!
+ use datafusion_common::config_field;
+
+ #[test]
+ fn test_macro() {
+ #[derive(Debug)]
+ struct E;
+
+ impl std::fmt::Display for E {
+ fn fmt(&self, _f: &mut std::fmt::Formatter<'_>) ->
std::fmt::Result {
+ unimplemented!()
+ }
+ }
+
+ impl std::error::Error for E {}
+
+ struct S;
+
+ impl std::str::FromStr for S {
+ type Err = E;
+
+ fn from_str(_s: &str) -> Result<Self, Self::Err> {
+ unimplemented!()
+ }
+ }
+
+ impl std::fmt::Display for S {
+ fn fmt(&self, _f: &mut std::fmt::Formatter<'_>) ->
std::fmt::Result {
+ unimplemented!()
+ }
+ }
+
+ config_field!(S);
+ }
+}
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