feat(filter): Add support for no_std environments

Co-authored-by: Çağatay Yiğit Şahin <cyigitsahin@outlook.com>

Author: WolverinDEV

crates/env_filter/Cargo.toml

@@ -26,11 +26,12 @@ pre-release-replacements = [
 ]
 
 [features]
-default = ["regex"]
-regex = ["dep:regex"]
+default = ["std", "regex"]
+regex = ["std", "dep:regex"]
+std = []
 
 [dependencies]
-log = { version = "0.4.29", features = ["std"] }
+log = { version = "0.4.29", default-features = false }
 regex = { version = "1.12.3", optional = true, default-features=false, features=["std", "perf"] }
 
 [dev-dependencies]

crates/env_filter/src/directive.rs

@@ -1,3 +1,5 @@
+use alloc::string::String;
+
 use log::Level;
 use log::LevelFilter;
 

crates/env_filter/src/filter.rs

@@ -1,12 +1,10 @@
-use std::env;
-use std::fmt;
-use std::mem;
+use alloc::{borrow::ToOwned, string::ToString, vec::Vec};
+use core::{fmt, mem};
 
 use log::{LevelFilter, Metadata, Record};
 
 use crate::enabled;
 use crate::parse_spec;
-use crate::parser::ParseResult;
 use crate::Directive;
 use crate::FilterOp;
 use crate::ParseError;
@@ -48,10 +46,11 @@ impl Builder {
     }
 
     /// Initializes the filter builder from an environment.
+    #[cfg(feature = "std")]
     pub fn from_env(env: &str) -> Builder {
         let mut builder = Builder::new();
 
-        if let Ok(s) = env::var(env) {
+        if let Ok(s) = std::env::var(env) {
             builder.parse(&s);
         }
 
@@ -98,10 +97,11 @@ impl Builder {
     /// See the [Enabling Logging] section for more details.
     ///
     /// [Enabling Logging]: ../index.html#enabling-logging
+    #[cfg(feature = "std")]
     pub fn parse(&mut self, filters: &str) -> &mut Self {
         #![allow(clippy::print_stderr)] // compatibility
 
-        let ParseResult {
+        let crate::parser::ParseResult {
             directives,
             filter,
             errors,

crates/env_filter/src/lib.rs

@@ -38,10 +38,13 @@
 //! ```
 
 #![cfg_attr(docsrs, feature(doc_cfg))]
+#![cfg_attr(not(feature = "std"), no_std)]
 #![warn(missing_docs)]
 #![warn(clippy::print_stderr)]
 #![warn(clippy::print_stdout)]
 
+extern crate alloc;
+
 mod directive;
 mod filter;
 mod filtered_log;

crates/env_filter/src/op.rs

@@ -1,4 +1,5 @@
-use std::fmt;
+use alloc::string::{String, ToString};
+use core::fmt;
 
 #[derive(Debug, Clone)]
 pub(crate) struct FilterOp {

crates/env_filter/src/parser.rs

@@ -1,6 +1,7 @@
+use alloc::{borrow::ToOwned, format, string::String, vec::Vec};
+use core::fmt::{Display, Formatter};
+
 use log::LevelFilter;
-use std::error::Error;
-use std::fmt::{Display, Formatter};
 
 use crate::Directive;
 use crate::FilterOp;
@@ -46,12 +47,16 @@ pub struct ParseError {
 }
 
 impl Display for ParseError {
-    fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
+    fn fmt(&self, f: &mut Formatter<'_>) -> core::fmt::Result {
         write!(f, "error parsing logger filter: {}", self.details)
     }
 }
 
-impl Error for ParseError {}
+#[cfg(feature = "std")]
+impl std::error::Error for ParseError {}
+
+#[cfg(not(feature = "std"))]
+impl core::error::Error for ParseError {}
 
 /// Parse a logging specification string (e.g: `crate1,crate2::mod3,crate3::x=error/foo`)
 /// and return a vector with log directives.