Use core::error (#5973)

Fixes #5964 

The only remaining uses of `std` are:
* `DataError::Io` and `DataError::with_path`
* `with_path` can be replaced by `with_display_context(path.display())`,
but the `std::io::ErrorKind` is not in `core` (it could be, it's a
fieldless enum).
* `icu_provider::log` falling back to `println!` (negative `logging`
feature)
* `icu_capi` keeps its std feature, as that's required to build a static
library with panic=unwind. I'm not sure what the use case for this is,
but we use it as a baseline in the size benchmark.

components/calendar/Cargo.toml

@@ -50,7 +50,6 @@ criterion = { workspace = true }
 default = ["compiled_data", "ixdtf"]
 ixdtf = ["dep:ixdtf"]
 logging = ["calendrical_calculations/logging"]
-std = ["icu_provider/std", "icu_locale_core/std", "calendrical_calculations/std"]
 serde = ["dep:serde", "zerovec/serde", "tinystr/serde", "icu_provider/serde"]
 datagen = ["serde", "dep:databake", "zerovec/databake", "tinystr/databake"]
 bench = []

components/calendar/src/error.rs

@@ -29,6 +29,8 @@ pub enum DateError {
     UnknownMonthCode(MonthCode),
 }
 
+impl core::error::Error for DateError {}
+
 #[derive(Debug, Copy, Clone, PartialEq, Display)]
 /// An argument is out of range for its domain.
 #[displaydoc("The {field} = {value} argument is out of range {min}..={max}")]
@@ -44,6 +46,8 @@ pub struct RangeError {
     pub max: i32,
 }
 
+impl core::error::Error for RangeError {}
+
 impl From<RangeError> for DateError {
     fn from(value: RangeError) -> Self {
         let RangeError {

components/calendar/src/lib.rs

@@ -94,7 +94,7 @@
 //! [`ICU4X`]: ../icu/index.html
 
 // https://github.com/unicode-org/icu4x/blob/main/documents/process/boilerplate.md#library-annotations
-#![cfg_attr(not(any(test, feature = "std")), no_std)]
+#![cfg_attr(not(any(test, doc)), no_std)]
 #![cfg_attr(
     not(test),
     deny(

components/casemap/Cargo.toml

@@ -45,7 +45,6 @@ criterion = { workspace = true }
 
 [features]
 default = ["compiled_data"]
-std = ["icu_collections/std", "icu_provider/std"]
 bench = []
 serde = ["dep:serde", "zerovec/serde", "icu_collections/serde", "icu_provider/serde", "icu_properties/serde", "potential_utf/serde"]
 datagen = ["serde", "dep:databake", "zerovec/databake", "icu_collections/databake"]

components/casemap/src/lib.rs

@@ -28,7 +28,7 @@
 //! [`ICU4X`]: ../icu/index.html
 
 // https://github.com/unicode-org/icu4x/blob/main/documents/process/boilerplate.md#library-annotations
-#![cfg_attr(not(any(test, feature = "std")), no_std)]
+#![cfg_attr(not(any(test, doc)), no_std)]
 #![cfg_attr(
     not(test),
     deny(

components/collator/Cargo.toml

@@ -48,7 +48,6 @@ criterion = { workspace = true }
 
 [features]
 default = ["compiled_data"]
-std = ["icu_collections/std", "icu_locale_core/std", "icu_normalizer/std", "icu_properties/std", "icu_provider/std"]
 serde = ["dep:serde", "zerovec/serde", "icu_properties/serde", "icu_normalizer/serde", "icu_collections/serde", "icu_provider/serde"]
 datagen = ["serde", "dep:databake", "zerovec/databake", "icu_properties/datagen", "icu_normalizer/datagen", "icu_collections/databake"]
 compiled_data = ["dep:icu_collator_data", "icu_normalizer/compiled_data"]

components/collator/src/lib.rs

@@ -7,7 +7,7 @@
 // described in LICENSE.
 
 // https://github.com/unicode-org/icu4x/blob/main/documents/process/boilerplate.md#library-annotations
-#![cfg_attr(not(any(test, feature = "std")), no_std)]
+#![cfg_attr(not(any(test, doc)), no_std)]
 #![cfg_attr(
     not(test),
     deny(

components/collections/Cargo.toml

@@ -44,7 +44,6 @@ toml = { workspace = true }
 criterion = { workspace = true }
 
 [features]
-std = []
 serde = ["dep:serde", "zerovec/serde", "potential_utf/serde"]
 databake = ["dep:databake", "zerovec/databake"]
 bench = []

components/collections/src/codepointtrie/error.rs

@@ -20,3 +20,5 @@ pub enum Error {
     #[displaydoc("CodePointTrie must be constructed from data vector with at least one element")]
     EmptyDataVector,
 }
+
+impl core::error::Error for Error {}

components/collections/src/lib.rs

@@ -21,7 +21,7 @@
 //! / [ICU4J CharsTrie](https://unicode-org.github.io/icu-docs/apidoc/released/icu4j/com/ibm/icu/util/CharsTrie.html) API.
 
 // https://github.com/unicode-org/icu4x/blob/main/documents/process/boilerplate.md#library-annotations
-#![cfg_attr(not(any(test, feature = "std")), no_std)]
+#![cfg_attr(not(any(test, doc)), no_std)]
 #![cfg_attr(
     not(test),
     deny(

components/datetime/Cargo.toml

@@ -63,14 +63,6 @@ criterion = { workspace = true }
 
 [features]
 default = ["compiled_data"]
-std = [
-    "icu_calendar/std",
-    "icu_decimal/std",
-    "icu_locale_core/std",
-    "icu_plurals/std",
-    "icu_provider/std",
-    "icu_timezone/std",
-]
 serde = [
     "dep:serde",
     "icu_calendar/serde",
@@ -93,7 +85,6 @@ datagen = [
     "icu_plurals/datagen",
     "icu_timezone/datagen",
     "serde",
-    "std",
 ]
 logging = ["icu_calendar/logging"]
 experimental = ["dep:litemap"]

components/datetime/src/builder.rs

@@ -163,6 +163,8 @@ pub enum BuilderError {
     InvalidOptions,
 }
 
+impl core::error::Error for BuilderError {}
+
 /// A builder for [dynamic field sets](crate::fieldsets::enums).
 ///
 /// This builder is useful if you do not know the field set at code compilation time. If you do,

components/datetime/src/error.rs

@@ -30,6 +30,8 @@ pub enum DateTimeFormatterLoadError {
     Data(DataError),
 }
 
+impl core::error::Error for DateTimeFormatterLoadError {}
+
 impl From<DataError> for DateTimeFormatterLoadError {
     fn from(error: DataError) -> Self {
         Self::Data(error)
@@ -52,6 +54,8 @@ pub struct MismatchedCalendarError {
     pub date_kind: Option<AnyCalendarKind>,
 }
 
+impl core::error::Error for MismatchedCalendarError {}
+
 #[non_exhaustive]
 #[derive(Debug, PartialEq, Copy, Clone, displaydoc::Display)]
 /// Error for `TryWriteable` implementations
@@ -129,3 +133,5 @@ pub enum DateTimeWriteError {
     #[displaydoc("Unsupported field {0:?}")]
     UnsupportedField(ErrorField),
 }
+
+impl core::error::Error for DateTimeWriteError {}

components/datetime/src/lib.rs

@@ -70,7 +70,7 @@
 //! ```
 
 // https://github.com/unicode-org/icu4x/blob/main/documents/process/boilerplate.md#library-annotations
-#![cfg_attr(not(any(test, feature = "std")), no_std)]
+#![cfg_attr(not(any(test, doc)), no_std)]
 #![cfg_attr(
     not(test),
     deny(

components/datetime/src/neo_serde.rs

@@ -34,6 +34,8 @@ pub enum CompositeFieldSetSerdeError {
     InvalidFields,
 }
 
+impl core::error::Error for CompositeFieldSetSerdeError {}
+
 /// 🚧 \[Experimental\] A type corresponding to [`CompositeFieldSet`] that implements
 /// [`serde::Serialize`] and [`serde::Deserialize`].
 ///

components/datetime/src/options/mod.rs

@@ -521,6 +521,8 @@ pub enum FractionalSecondError {
     OutOfRange,
 }
 
+impl core::error::Error for FractionalSecondError {}
+
 impl From<FractionalSecondDigits> for u8 {
     fn from(value: FractionalSecondDigits) -> u8 {
         use FractionalSecondDigits::*;

components/datetime/src/pattern/mod.rs

@@ -89,3 +89,5 @@ pub enum PatternLoadError {
     #[displaydoc("Problem loading data for field {1:?}: {0}")]
     Data(icu_provider::DataError, ErrorField),
 }
+
+impl core::error::Error for PatternLoadError {}

components/datetime/src/provider/fields/length.rs

@@ -17,8 +17,7 @@ pub enum LengthError {
     InvalidLength,
 }
 
-#[cfg(feature = "std")]
-impl std::error::Error for LengthError {}
+impl core::error::Error for LengthError {}
 
 /// An enum representing the length of a field within a date or time formatting pattern string.
 ///

components/datetime/src/provider/fields/mod.rs

@@ -36,8 +36,7 @@ pub enum Error {
     InvalidLength(FieldSymbol),
 }
 
-#[cfg(feature = "std")]
-impl std::error::Error for Error {}
+impl core::error::Error for Error {}
 
 /// A field within a date pattern string, also referred to as a date field.
 ///

components/datetime/src/provider/fields/symbols.rs

@@ -26,8 +26,7 @@ pub enum SymbolError {
     Invalid(u8),
 }
 
-#[cfg(feature = "std")]
-impl std::error::Error for SymbolError {}
+impl core::error::Error for SymbolError {}
 
 /// A field symbol for a date formatting pattern.
 ///

components/datetime/src/provider/pattern/error.rs

@@ -30,8 +30,7 @@ pub enum PatternError {
     UnsupportedPluralPivot,
 }
 
-#[cfg(feature = "std")]
-impl std::error::Error for PatternError {}
+impl core::error::Error for PatternError {}
 
 impl From<fields::Error> for PatternError {
     fn from(input: fields::Error) -> Self {

components/datetime/src/provider/skeleton/error.rs

@@ -32,8 +32,7 @@ pub enum SkeletonError {
     Fields(fields::Error),
 }
 
-#[cfg(feature = "std")]
-impl std::error::Error for SkeletonError {}
+impl core::error::Error for SkeletonError {}
 
 impl From<fields::Error> for SkeletonError {
     fn from(e: fields::Error) -> Self {

components/datetime/src/provider/skeleton/serde.rs

@@ -3,6 +3,8 @@
 // (online at: https://github.com/unicode-org/icu4x/blob/main/LICENSE ).
 
 use alloc::format;
+#[cfg(feature = "datagen")]
+use alloc::string::ToString;
 use core::convert::TryFrom;
 use smallvec::SmallVec;
 
@@ -75,11 +77,12 @@ pub mod reference {
 
 pub mod runtime {
     use super::super::runtime::Skeleton;
-    use zerovec::ZeroVec;
+    use super::*;
 
     #[cfg(feature = "datagen")]
     use ::serde::{ser, Serialize};
     use serde::{de, Deserialize, Deserializer};
+    use zerovec::ZeroVec;
     /// This is an implementation of the serde deserialization visitor pattern.
     #[allow(clippy::upper_case_acronyms)]
     struct DeserializeSkeletonUTS35String;

components/datetime/src/scaffold/names_storage.rs

@@ -76,13 +76,17 @@ impl_holder_trait!(tz::MzPeriodV1Marker);
 
 /// An error returned by [`MaybePayload`].
 #[allow(missing_docs)]
-#[derive(Debug)]
+#[derive(Debug, displaydoc::Display)]
 #[non_exhaustive]
 pub enum MaybePayloadError {
+    /// TODO
     TypeTooSpecific,
+    /// TODO
     ConflictingField,
 }
 
+impl core::error::Error for MaybePayloadError {}
+
 impl MaybePayloadError {
     pub(crate) fn into_load_error(self, error_field: ErrorField) -> PatternLoadError {
         match self {

components/decimal/Cargo.toml

@@ -46,7 +46,6 @@ criterion = { workspace = true }
 
 [features]
 default = ["compiled_data"]
-std = ["fixed_decimal/std", "icu_locale_core/std", "icu_provider/std"]
 serde = ["dep:serde", "icu_provider/serde", "zerovec/serde", "tinystr/serde"]
 datagen = ["serde", "dep:databake", "zerovec/databake", "tinystr/databake"]
 bench = ["serde"]

components/decimal/src/lib.rs

@@ -76,7 +76,7 @@
 //! [`FixedDecimalFormatter`]: FixedDecimalFormatter
 
 // https://github.com/unicode-org/icu4x/blob/main/documents/process/boilerplate.md#library-annotations
-#![cfg_attr(not(any(test, feature = "std")), no_std)]
+#![cfg_attr(not(any(test, doc)), no_std)]
 #![cfg_attr(
     not(test),
     deny(

components/experimental/Cargo.toml

@@ -71,10 +71,9 @@ icu_normalizer_data = { workspace = true }
 [features]
 default = ["compiled_data"]
 compiled_data = ["dep:icu_experimental_data", "icu_decimal/compiled_data", "icu_list/compiled_data", "icu_plurals/compiled_data", "icu_properties/compiled_data", "icu_normalizer/compiled_data"]
-datagen = ["serde", "std", "dep:databake", "zerovec/databake", "zerotrie/databake", "tinystr/databake", "icu_collections/databake", "std", "log", "icu_pattern/databake", "icu_plurals/datagen", "icu_pattern/alloc"]
+datagen = ["serde", "dep:databake", "zerovec/databake", "zerotrie/databake", "tinystr/databake", "icu_collections/databake", "log", "icu_pattern/databake", "icu_plurals/datagen", "icu_pattern/alloc"]
 ryu = ["fixed_decimal/ryu"]
 serde = ["dep:serde", "zerovec/serde", "potential_utf/serde", "tinystr/serde", "icu_collections/serde", "icu_decimal/serde", "icu_list/serde", "icu_pattern/serde", "icu_plurals/serde", "icu_provider/serde", "zerotrie/serde", "icu_normalizer/serde"]
-std = ["fixed_decimal/std", "icu_decimal/std", "icu_pattern/std", "icu_plurals/std", "icu_provider/std", "icu_locale_core/std"]
 
 bench = []
 

components/experimental/src/compactdecimal/error.rs

@@ -17,3 +17,5 @@ pub struct ExponentError {
     /// The magnitude of the number being formatted.
     pub(crate) log10_type: i16,
 }
+
+impl core::error::Error for ExponentError {}

components/experimental/src/duration/validated_options.rs

@@ -83,6 +83,8 @@ pub enum DurationFormatterOptionsError {
     FractionalDigitsOutOfRange,
 }
 
+impl core::error::Error for DurationFormatterOptionsError {}
+
 impl ValidatedDurationFormatterOptions {
     pub fn validate(
         value: DurationFormatterOptions,

components/experimental/src/lib.rs

@@ -11,7 +11,7 @@
 //! crate will eventually stabilize and move to their own top-level components.
 
 // https://github.com/unicode-org/icu4x/blob/main/documents/process/boilerplate.md#library-annotations
-#![cfg_attr(not(any(test, feature = "std")), no_std)]
+#![cfg_attr(not(any(test, doc)), no_std)]
 // No boilerplate, each module has their own
 #![allow(clippy::module_inception)]
 

components/experimental/src/personnames/api.rs

@@ -49,6 +49,8 @@ pub enum PersonNamesFormatterError {
     Pattern(icu_pattern::Error),
 }
 
+impl core::error::Error for PersonNamesFormatterError {}
+
 impl From<DataError> for PersonNamesFormatterError {
     fn from(e: DataError) -> Self {
         PersonNamesFormatterError::Data(e)

components/experimental/src/transliterate/compile/mod.rs

@@ -491,7 +491,7 @@ where
         + DataProvider<XidStartV1Marker>,
     NP: ?Sized,
 {
-    fn iter_ids(&self) -> Result<std::collections::BTreeSet<DataIdentifierCow>, DataError> {
+    fn iter_ids(&self) -> Result<alloc::collections::BTreeSet<DataIdentifierCow>, DataError> {
         let exclusive_data = self.collection.data.borrow();
         Ok(exclusive_data
             .0

components/experimental/src/transliterate/transliterator/mod.rs

@@ -194,7 +194,7 @@ type Env = LiteMap<String, InternalTransliterator>;
 /// #[derive(Debug)]
 /// struct AsciiUpperTransliterator;
 /// impl CustomTransliterator for AsciiUpperTransliterator {
-///     fn transliterate(&self, input: &str, range: std::ops::Range<usize>) -> String {
+///     fn transliterate(&self, input: &str, range: core::ops::Range<usize>) -> String {
 ///         input.to_ascii_uppercase()
 ///     }
 /// }

components/experimental/src/units/ratio.rs

@@ -61,6 +61,8 @@ pub enum RatioFromStrError {
     ParsingBigIntError(num_bigint::ParseBigIntError),
 }
 
+impl core::error::Error for RatioFromStrError {}
+
 impl IcuRatio {
     /// Creates a new `IcuRatio` from the given numerator and denominator.
     pub fn from_big_ints(numerator: BigInt, denominator: BigInt) -> Self {

components/icu/Cargo.toml

@@ -66,23 +66,6 @@ default = [
     "icu_experimental?/default",
     "icu_pattern?/default",
 ]
-std = [
-    "icu_calendar/std",
-    "icu_casemap/std",
-    "icu_collator/std",
-    "icu_collections/std",
-    "icu_datetime/std",
-    "icu_decimal/std",
-    "icu_list/std",
-    "icu_locale/std",
-    "icu_normalizer/std",
-    "icu_plurals/std",
-    "icu_properties/std",
-    "icu_segmenter/std",
-    "icu_timezone/std",
-    "icu_experimental?/std",
-    "icu_pattern?/std",
-]
 serde = [
     "icu_calendar/serde",
     "icu_casemap/serde",
@@ -116,7 +99,6 @@ compiled_data = [
     "icu_experimental?/compiled_data",
 ]
 datagen = [
-    "std",
     "dep:icu_provider_registry",
     "dep:memchr",
     "icu_calendar/datagen",