Add a special rule for string literals that omits the unwrap call.

Using `avr_progmem_string::string_as_bytes` macro, string literals can be
converted into fixed-sized byte arrays allowing to use the
`PmString::from_array` constructor, thus removing the `unwrap`, and
consequently the necessity for the `const_option` Compiler feature.

Cargo.toml

@@ -43,6 +43,12 @@ cfg-if = "1.0"
 version = "0.1.0"
 optional = true
 
+[dependencies.avr-progmem-string]
+# TODO: upgrade to a crates.io version
+git = "https://github.com/mutantbob/avr-progmem-string.git"
+rev = "2dc98b809a99098f70d38a8d1653d9cc6664e16e"
+
+
 
 [dev-dependencies]
 panic-halt = "0.2.0"

examples/uno-arrays.rs

@@ -7,11 +7,6 @@
 // Define no_std only for AVR
 #![cfg_attr(target_arch = "avr", no_std)]
 #![cfg_attr(target_arch = "avr", no_main)]
-//
-// To unwrap the Option in const context
-#![feature(const_option)]
-//
-#![feature(extended_key_value_attributes)]
 
 
 use avr_progmem::progmem; // The macro

src/string.rs

@@ -85,8 +85,6 @@
 //! Using [`PmString`] directly via the [`progmem`] macro:
 //!
 //! ```rust
-//! #![feature(const_option)]
-//!
 //! # use std::iter::FromIterator;
 //! use avr_progmem::progmem;
 //! use avr_progmem::string::LoadedString;
@@ -95,8 +93,6 @@
 //!     // A simple Unicode string in progmem, internally stored as fix-sized
 //!     // byte array, i.e. a `PmString<18>`.
 //!     static progmem string TEXT = "Hello 大賢者";
-//!     // text too large to fit in the RAM of a microcontroller
-//!     static progmem string LOVECRAFT = include_str!("../examples/test_text.txt");
 //! }
 //!
 //! // You can load it all at once (like a `ProgMem`)
@@ -132,8 +128,6 @@
 //! [`progmem_display`]:
 //!
 //! ```rust
-//! #![feature(const_option)]
-//!
 //! use avr_progmem::progmem_str as F;
 //! use avr_progmem::progmem_display as D;
 //!
@@ -159,6 +153,38 @@
 //! ufmt::uwrite!(&mut writer, "{}", D!("Hello 大賢者"));
 //! ```
 //!
+//! You can also use arbitrary `&str`-yielding expression, however,
+//! then you need Rust's `const_option` feature, because the string size
+//! can no longer be determined statically.
+//!
+//! ```rust
+//! #![feature(const_option)]
+//!
+//! use avr_progmem::progmem;
+//! use avr_progmem::progmem_display as D;
+//! #
+//! # use ufmt::uWrite;
+//! # struct MyWriter;
+//! # impl uWrite for MyWriter {
+//! #     type Error = ();
+//! #     fn write_str(&mut self, _s: &str) -> Result<(),()> {
+//! #         Ok(()) // ignore input
+//! #     }
+//! # }
+//! # let mut writer =
+//! #   MyWriter
+//! #    /* SNIP */;
+//!
+//! progmem! {
+//!     // Text too large to fit in the RAM of a microcontroller
+//!     static progmem string LOVECRAFT = include_str!("../examples/test_text.txt");
+//! }
+//!
+//! // In-line a huge string from a file
+//! #[cfg(feature = "ufmt")] // requires the `ufmt` crate feature
+//! ufmt::uwrite!(&mut writer, "{}", D!(include_str!("../examples/test_text.txt")));
+//! ```
+//!
 
 
 use core::convert::TryFrom;

src/wrapper.rs

@@ -19,6 +19,10 @@
 
 use core::convert::TryInto;
 
+// Used in the `progmem` macro
+#[doc(hidden)]
+pub use avr_progmem_string::string_as_bytes;
+
 use crate::raw::read_value;
 
 
@@ -530,7 +534,40 @@ macro_rules! progmem {
 #[doc(hidden)]
 #[macro_export]
 macro_rules! progmem_internal {
-	// The string rule creating the progmem string static via `PmString`
+	// A string rule creating the progmem string static from a string literal
+	// using `string_as_bytes`, so no `unwrap` is required
+	{
+		$( #[ $attr:meta ] )*
+		$vis:vis static progmem string $name:ident = $value:literal ;
+	} => {
+
+		// PmString must be stored in the progmem or text section!
+		// The link_section lets us define it:
+		#[cfg_attr(target_arch = "avr", link_section = ".progmem.data")]
+
+		// User attributes
+		$(#[$attr])*
+		// The actual static definition
+		$vis static $name : $crate::string::PmString<{
+			// This bit runs at compile-time
+			let s: &str = $value;
+			s.len()
+		}> =
+			unsafe {
+				// SAFETY: This call is sound, be cause we ensure with the above
+				// link_section attribute that this value is indeed in the
+				// progmem section.
+				$crate::string::PmString::from_array(
+					// Using `avr_progmem_string::string_as_bytes` macro to get
+					// a fixed size array, so there is no need for an `unwrap`
+					// anymore.
+					$crate::wrapper::string_as_bytes!( $value )
+				)
+			};
+	};
+
+	// The string rule creating the progmem string static from an arbitrary
+	// string expression, thus a unwrap is needed.
 	{
 		$( #[ $attr:meta ] )*
 		$vis:vis static progmem string $name:ident = $value:expr ;