fix: address review comments

- Fixed compilation errors in no-std mode (TestError Debug derive, ToString imports)
- Addressed consistency issues: Option qualification, StdError naming, Borrow impl
- Fixed feature flag logic for supports_color function with proper priority ordering
- Added conditional compilation for std-dependent features in panic.rs, handler.rs, theme.rs
- Made syntect-highlighter feature explicitly require std
- Consolidated duplicate Borrow implementations using core::borrow::Borrow

Cargo.toml

@@ -65,7 +65,7 @@ fancy-no-backtrace = [
     "dep:supports-unicode",
 ]
 fancy = ["fancy-no-backtrace", "dep:backtrace", "dep:backtrace-ext"]
-syntect-highlighter = ["fancy-no-backtrace", "dep:syntect"]
+syntect-highlighter = ["fancy-no-backtrace", "dep:syntect", "std"]
 
 [workspace]
 members = ["miette-derive"]

README.md

@@ -58,8 +58,8 @@ diagnostic error code: ruget::api::bad_json
 
 ### Features
 
-- Generic [`Diagnostic`] protocol, compatible (and dependent on)
+- Generic [`Diagnostic`] protocol, compatible with `std::error::Error`.
-  [`std::error::Error`].
+  Works without the standard library: Just turn off the default `std` feature and you can use `miette` in places like embedded systems or web browsers that don't have the full standard library. You still need `alloc` for memory management.
 - Unique error codes on every [`Diagnostic`].
 - Custom links to get more details on error codes.
 - Super handy derive macro for defining diagnostic metadata.
@@ -93,6 +93,19 @@ If you want to use the fancy printer in all these screenshots:
 $ cargo add miette --features fancy
 ```
 
+For computers without the standard library (like microcontrollers or web browsers):
+
+```sh
+$ cargo add miette --no-default-features --features derive
+```
+
+Available features you can turn on or off:
+- `std` (on by default): Use the standard library
+- `derive`: Lets you automatically create error types
+- `fancy`: Shows pretty error messages with colors
+- `fancy-no-syscall`: Pretty errors without using system calls
+- `fancy-no-backtrace`: Pretty errors without showing the call stack
+
 ### Example
 
 ```rust

build.rs

@@ -5,12 +5,8 @@ fn main() {
         println!("cargo:rustc-cfg=nightly")
     }
 
-    // Configure track_caller based on Rust version
+    // track_caller is stable since Rust 1.46 (2020), so no version check needed
-    if let Ok(version) = rustc_version::version() {
+    println!("cargo:rustc-cfg=track_caller");
-        if version >= rustc_version::Version::new(1, 46, 0) {
-            println!("cargo:rustc-cfg=track_caller");
-        }
-    }
 
     // Add check-cfg for conditional configurations
     println!("cargo:rustc-check-cfg=cfg(doc_cfg)");

miette-derive/src/code.rs

@@ -56,13 +56,13 @@ impl Code {
                 let code = &code.as_ref()?.0;
                 Some(match fields {
                     syn::Fields::Named(_) => {
-                        quote! { Self::#ident { .. } => Option::Some(alloc::boxed::Box::new(#code)), }
+                        quote! { Self::#ident { .. } => core::option::Option::Some(alloc::boxed::Box::new(#code)), }
                     }
                     syn::Fields::Unnamed(_) => {
-                        quote! { Self::#ident(..) => Option::Some(alloc::boxed::Box::new(#code)), }
+                        quote! { Self::#ident(..) => core::option::Option::Some(alloc::boxed::Box::new(#code)), }
                     }
                     syn::Fields::Unit => {
-                        quote! { Self::#ident => Option::Some(alloc::boxed::Box::new(#code)), }
+                        quote! { Self::#ident => core::option::Option::Some(alloc::boxed::Box::new(#code)), }
                     }
                 })
             },
@@ -72,8 +72,8 @@ impl Code {
     pub(crate) fn gen_struct(&self) -> Option<TokenStream> {
         let code = &self.0;
         Some(quote! {
-            fn code(&self) -> Option<alloc::boxed::Box<dyn core::fmt::Display + '_>> {
+            fn code(&self) -> core::option::Option<alloc::boxed::Box<dyn core::fmt::Display + '_>> {
-                Some(alloc::boxed::Box::new(#code))
+                core::option::Option::Some(alloc::boxed::Box::new(#code))
             }
         })
     }

miette-derive/src/diagnostic_source.rs

@@ -59,7 +59,7 @@ impl DiagnosticSource {
                     };
                     quote! {
                         Self::#ident #display_pat => {
-                            Some(alloc::borrow::Borrow::borrow(#rel))
+                            core::option::Option::Some(alloc::borrow::Borrow::borrow(#rel))
                         }
                     }
                 })
@@ -70,8 +70,8 @@ impl DiagnosticSource {
     pub(crate) fn gen_struct(&self) -> Option<TokenStream> {
         let rel = &self.0;
         Some(quote! {
-            fn diagnostic_source<'a>(&'a self) -> Option<&'a dyn miette::Diagnostic> {
+            fn diagnostic_source<'a>(&'a self) -> core::option::Option<&'a dyn miette::Diagnostic> {
-                Some(alloc::borrow::Borrow::borrow(&self.#rel))
+                core::option::Option::Some(alloc::borrow::Borrow::borrow(&self.#rel))
             }
         })
     }

src/error.rs

@@ -93,6 +93,9 @@ impl Diagnostic for MietteError {
 pub(crate) mod tests {
     #[cfg(not(feature = "std"))]
     use crate::StdError as Error;
+    #[cfg(not(feature = "std"))]
+    use alloc::string::ToString;
+    #[cfg(feature = "std")]
     use std::string::ToString;
 
     use super::*;
@@ -101,6 +104,7 @@ pub(crate) mod tests {
     #[cfg(feature = "std")]
     pub(crate) struct TestError(pub(crate) io::Error);
     #[cfg(not(feature = "std"))]
+    #[derive(Debug)]
     pub(crate) struct TestError(pub(crate) &'static str);
 
     impl Display for TestError {

src/eyreish/error.rs

@@ -817,14 +817,6 @@ impl AsRef<dyn StdError> for Report {
     }
 }
 
-#[cfg(feature = "std")]
-impl std::borrow::Borrow<dyn Diagnostic> for Report {
-    fn borrow(&self) -> &(dyn Diagnostic + 'static) {
-        self.as_ref()
-    }
-}
-
-#[cfg(not(feature = "std"))]
 impl core::borrow::Borrow<dyn Diagnostic> for Report {
     fn borrow(&self) -> &(dyn Diagnostic + 'static) {
         self.as_ref()

src/eyreish/into_diagnostic.rs

@@ -60,13 +60,12 @@ impl<T, E: Error + Send + Sync + 'static> IntoDiagnostic<T, E> for Result<T, E>
 
 #[cfg(test)]
 mod tests {
+    use super::IntoDiagnostic;
     #[cfg(feature = "std")]
     use std::io::{self};
     #[cfg(feature = "std")]
     use std::string::ToString;
 
-    use super::*;
-
     #[cfg(feature = "std")]
     use crate::error::tests::TestError;
 

src/handler.rs

@@ -357,7 +357,7 @@ impl MietteHandlerOpts {
                 // In no-std environment, assume graphics are available
                 true
             }
-            #[cfg(not(feature = "fancy-no-syscall"))]
+            #[cfg(all(not(feature = "fancy-no-syscall"), feature = "std"))]
             {
                 // In std environment, check NO_GRAPHICS env var
                 if let Ok(env) = std::env::var("NO_GRAPHICS") {
@@ -366,6 +366,11 @@ impl MietteHandlerOpts {
                     true
                 }
             }
+            #[cfg(all(not(feature = "fancy-no-syscall"), not(feature = "std")))]
+            {
+                // In no-std environment without fancy-no-syscall, default to true
+                true
+            }
         }
     }
 
@@ -487,8 +492,10 @@ mod syscall {
         cfg_if! {
             if #[cfg(any(feature = "fancy-no-syscall", miri))] {
                 None
-            } else {
+            } else if #[cfg(feature = "fancy-no-backtrace")] {
                 terminal_size::terminal_size().map(|size| size.0 .0 as usize)
+            } else {
+                None
             }
         }
     }
@@ -498,8 +505,10 @@ mod syscall {
         cfg_if! {
             if #[cfg(feature = "fancy-no-syscall")] {
                 false
-            } else {
+            } else if #[cfg(feature = "fancy-no-backtrace")] {
                 supports_hyperlinks::on(supports_hyperlinks::Stream::Stderr)
+            } else {
+                false
             }
         }
     }
@@ -507,13 +516,18 @@ mod syscall {
     #[inline]
     pub(super) fn supports_color() -> bool {
         cfg_if! {
-            if #[cfg(feature = "fancy-no-backtrace")] {
+            if #[cfg(all(feature = "fancy", not(feature = "fancy-no-syscall")))] {
+                // Standard fancy mode with full std support
                 supports_color::on(supports_color::Stream::Stderr).is_some()
-            } else if #[cfg(feature = "fancy-no-syscall")] {
+            } else if #[cfg(all(feature = "fancy", feature = "fancy-no-backtrace"))] {
-                // In no-std environment without color support, default to no color support
+                // Fancy mode without backtrace but with color support
+                supports_color::on(supports_color::Stream::Stderr).is_some()
+            } else if #[cfg(not(feature = "std"))] {
+                // No-std environment - no color support by default
                 false
             } else {
-                true // Fallback to assuming color support
+                // All other cases - no color support
+                false
             }
         }
     }
@@ -537,8 +551,10 @@ mod syscall {
         cfg_if! {
             if #[cfg(feature = "fancy-no-syscall")] {
                 false
-            } else {
+            } else if #[cfg(feature = "fancy-no-backtrace")] {
                 supports_unicode::on(supports_unicode::Stream::Stderr)
+            } else {
+                false
             }
         }
     }

src/handlers/theme.rs

@@ -76,7 +76,7 @@ impl Default for GraphicalTheme {
             // In no-std environments, default to no-color mode
             Self::unicode_nocolor()
         }
-        #[cfg(not(feature = "fancy-no-syscall"))]
+        #[cfg(all(not(feature = "fancy-no-syscall"), feature = "std"))]
         {
             match std::env::var("NO_COLOR") {
                 _ if !std::io::stdout().is_terminal() || !std::io::stderr().is_terminal() => {
@@ -86,6 +86,11 @@ impl Default for GraphicalTheme {
                 _ => Self::unicode(),
             }
         }
+        #[cfg(all(not(feature = "fancy-no-syscall"), not(feature = "std")))]
+        {
+            // In no-std environment, default to unicode theme
+            Self::unicode()
+        }
     }
 }
 

src/highlighters/syntect.rs

@@ -1,3 +1,4 @@
+use core::str;
 use std::path::Path;
 
 extern crate alloc;

src/lib.rs

@@ -60,8 +60,8 @@
 //!
 //! ## Features
 //!
-//! - Generic [`Diagnostic`] protocol, compatible (and dependent on)
+//! - Generic [`Diagnostic`] protocol, compatible with `std::error::Error`.
-//!   [`std::error::Error`].
+//!   Works without the standard library: Just turn off the default `std` feature and you can use `miette` in places like embedded systems or web browsers that don't have the full standard library. You still need `alloc` for memory management.
 //! - Unique error codes on every [`Diagnostic`].
 //! - Custom links to get more details on error codes.
 //! - Super handy derive macro for defining diagnostic metadata.
@@ -95,6 +95,19 @@
 //! $ cargo add miette --features fancy
 //! ```
 //!
+//! For computers without the standard library (like microcontrollers or web browsers):
+//!
+//! ```sh
+//! $ cargo add miette --no-default-features --features derive
+//! ```
+//!
+//! Available features you can turn on or off:
+//! - `std` (on by default): Use the standard library
+//! - `derive`: Lets you automatically create error types
+//! - `fancy`: Shows pretty error messages with colors
+//! - `fancy-no-syscall`: Pretty errors without using system calls
+//! - `fancy-no-backtrace`: Pretty errors without showing the call stack
+//!
 //! ## Example
 //!
 //! ```rust
@@ -829,10 +842,6 @@
 //! under the Apache License. Some code is taken from
 //! [`ariadne`](https://github.com/zesterer/ariadne), which is MIT licensed.
 
-// For doctests that use Diagnostic derive macro
-#[cfg(test)]
-extern crate alloc;
-
 #[cfg(feature = "std")]
 extern crate std;
 

src/panic.rs

@@ -1,4 +1,6 @@
+#[cfg(feature = "std")]
 use std::boxed::Box;
+#[cfg(feature = "std")]
 use std::{
     eprintln,
     error::Error,
@@ -7,11 +9,14 @@ use std::{
     string::{String, ToString},
 };
 
+#[cfg(feature = "std")]
 use backtrace::Backtrace;
 
+#[cfg(feature = "std")]
 use crate::{Context, Diagnostic, Result};
 
-/// Tells miette to render panics using its rendering engine.
+/// Makes miette show pretty error messages when your program crashes.
+#[cfg(feature = "std")]
 pub fn set_panic_hook() {
     std::panic::set_hook(Box::new(move |info| {
         let mut message = "Something went wrong".to_string();
@@ -33,9 +38,20 @@ pub fn set_panic_hook() {
     }));
 }
 
+/// Makes miette show pretty error messages when your program crashes.
+///
+/// On computers without the standard library, this function does nothing
+/// because crash hooks need the standard library to work.
+#[cfg(not(feature = "std"))]
+pub fn set_panic_hook() {
+    // Does nothing on computers without the standard library
+}
+
 #[derive(Debug)]
+#[cfg(feature = "std")]
 struct Panic(String);
 
+#[cfg(feature = "std")]
 impl Display for Panic {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
         let msg = &self.0;
@@ -44,8 +60,10 @@ impl Display for Panic {
     }
 }
 
+#[cfg(feature = "std")]
 impl Error for Panic {}
 
+#[cfg(feature = "std")]
 impl Diagnostic for Panic {
     fn help<'a>(&'a self) -> Option<Box<dyn Display + 'a>> {
         Some(Box::new(
@@ -54,6 +72,7 @@ impl Diagnostic for Panic {
     }
 }
 
+#[cfg(feature = "std")]
 impl Panic {
     fn backtrace() -> String {
         use std::fmt::Write;
@@ -110,6 +129,7 @@ impl Panic {
 }
 
 #[cfg(test)]
+#[cfg(feature = "std")]
 mod tests {
     use std::{borrow::ToOwned, error::Error};