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-rw-r--r--syn/examples/lazy-static/Cargo.toml2
-rw-r--r--syn/examples/lazy-static/README.md42
-rw-r--r--syn/examples/lazy-static/example/Cargo.toml10
-rw-r--r--syn/examples/lazy-static/example/src/main.rs20
-rw-r--r--syn/examples/lazy-static/lazy-static/Cargo.toml14
-rw-r--r--syn/examples/lazy-static/lazy-static/src/lib.rs143
6 files changed, 231 insertions, 0 deletions
diff --git a/syn/examples/lazy-static/Cargo.toml b/syn/examples/lazy-static/Cargo.toml
new file mode 100644
index 0000000..586e547
--- /dev/null
+++ b/syn/examples/lazy-static/Cargo.toml
@@ -0,0 +1,2 @@
+[workspace]
+members = ["example", "lazy-static"]
diff --git a/syn/examples/lazy-static/README.md b/syn/examples/lazy-static/README.md
new file mode 100644
index 0000000..bc64585
--- /dev/null
+++ b/syn/examples/lazy-static/README.md
@@ -0,0 +1,42 @@
+An example of parsing a custom syntax within a `functionlike!(...)` procedural
+macro. Demonstrates how to trigger custom warnings and error messages on
+individual tokens of the input.
+
+- [`lazy-static/src/lib.rs`](lazy-static/src/lib.rs)
+- [`example/src/main.rs`](example/src/main.rs)
+
+The library implements a `lazy_static!` macro similar to the one from the real
+[`lazy_static`](https://docs.rs/lazy_static/1.0.0/lazy_static/) crate on
+crates.io.
+
+```rust
+lazy_static! {
+ static ref USERNAME: Regex = Regex::new("^[a-z0-9_-]{3,16}$").unwrap();
+}
+```
+
+Compile and run the example by doing `cargo run` in the directory of the
+`example` crate.
+
+The implementation shows how to trigger custom warnings and error messages on
+the macro input. For example if you try adding an uncreatively named `FOO` lazy
+static, the macro will scold you with the following warning.
+
+```
+warning: come on, pick a more creative name
+ --> src/main.rs:10:16
+ |
+10 | static ref FOO: String = "lazy_static".to_owned();
+ | ^^^
+```
+
+And if you try to lazily initialize `() = ()`, the macro will outright refuse to
+compile it for you.
+
+```
+error: I can't think of a legitimate use for lazily initializing the value `()`
+ --> src/main.rs:10:27
+ |
+10 | static ref UNIT: () = ();
+ | ^^
+```
diff --git a/syn/examples/lazy-static/example/Cargo.toml b/syn/examples/lazy-static/example/Cargo.toml
new file mode 100644
index 0000000..716b08c
--- /dev/null
+++ b/syn/examples/lazy-static/example/Cargo.toml
@@ -0,0 +1,10 @@
+[package]
+name = "example"
+version = "0.0.0"
+authors = ["David Tolnay <dtolnay@gmail.com>"]
+edition = "2018"
+publish = false
+
+[dependencies]
+lazy_static = { path = "../lazy-static" }
+regex = "0.2"
diff --git a/syn/examples/lazy-static/example/src/main.rs b/syn/examples/lazy-static/example/src/main.rs
new file mode 100644
index 0000000..c4f64af
--- /dev/null
+++ b/syn/examples/lazy-static/example/src/main.rs
@@ -0,0 +1,20 @@
+use lazy_static::lazy_static;
+use regex::Regex;
+
+lazy_static! {
+ static ref USERNAME: Regex = {
+ println!("Compiling username regex...");
+ Regex::new("^[a-z0-9_-]{3,16}$").unwrap()
+ };
+}
+
+fn main() {
+ println!("Let's validate some usernames.");
+ validate("fergie");
+ validate("will.i.am");
+}
+
+fn validate(name: &str) {
+ // The USERNAME regex is compiled lazily the first time its value is accessed.
+ println!("is_match({:?}): {}", name, USERNAME.is_match(name));
+}
diff --git a/syn/examples/lazy-static/lazy-static/Cargo.toml b/syn/examples/lazy-static/lazy-static/Cargo.toml
new file mode 100644
index 0000000..bf65787
--- /dev/null
+++ b/syn/examples/lazy-static/lazy-static/Cargo.toml
@@ -0,0 +1,14 @@
+[package]
+name = "lazy_static"
+version = "0.0.0"
+authors = ["David Tolnay <dtolnay@gmail.com>"]
+edition = "2018"
+publish = false
+
+[lib]
+proc-macro = true
+
+[dependencies]
+proc-macro2 = { version = "1.0", features = ["nightly"] }
+quote = "1.0"
+syn = { path = "../../../", features = ["full"] }
diff --git a/syn/examples/lazy-static/lazy-static/src/lib.rs b/syn/examples/lazy-static/lazy-static/src/lib.rs
new file mode 100644
index 0000000..254ca72
--- /dev/null
+++ b/syn/examples/lazy-static/lazy-static/src/lib.rs
@@ -0,0 +1,143 @@
+#![recursion_limit = "128"]
+#![feature(proc_macro_diagnostic)]
+
+extern crate proc_macro;
+use self::proc_macro::TokenStream;
+
+use quote::{quote, quote_spanned};
+use syn::parse::{Parse, ParseStream, Result};
+use syn::spanned::Spanned;
+use syn::{parse_macro_input, Expr, Ident, Token, Type, Visibility};
+
+/// Parses the following syntax, which aligns with the input of the real
+/// `lazy_static` crate.
+///
+/// lazy_static! {
+/// $VISIBILITY static ref $NAME: $TYPE = $EXPR;
+/// }
+///
+/// For example:
+///
+/// lazy_static! {
+/// static ref USERNAME: Regex = Regex::new("^[a-z0-9_-]{3,16}$").unwrap();
+/// }
+struct LazyStatic {
+ visibility: Visibility,
+ name: Ident,
+ ty: Type,
+ init: Expr,
+}
+
+impl Parse for LazyStatic {
+ fn parse(input: ParseStream) -> Result<Self> {
+ let visibility: Visibility = input.parse()?;
+ input.parse::<Token![static]>()?;
+ input.parse::<Token![ref]>()?;
+ let name: Ident = input.parse()?;
+ input.parse::<Token![:]>()?;
+ let ty: Type = input.parse()?;
+ input.parse::<Token![=]>()?;
+ let init: Expr = input.parse()?;
+ input.parse::<Token![;]>()?;
+ Ok(LazyStatic {
+ visibility,
+ name,
+ ty,
+ init,
+ })
+ }
+}
+
+#[proc_macro]
+pub fn lazy_static(input: TokenStream) -> TokenStream {
+ let LazyStatic {
+ visibility,
+ name,
+ ty,
+ init,
+ } = parse_macro_input!(input as LazyStatic);
+
+ // The warning looks like this.
+ //
+ // warning: come on, pick a more creative name
+ // --> src/main.rs:10:16
+ // |
+ // 10 | static ref FOO: String = "lazy_static".to_owned();
+ // | ^^^
+ if name == "FOO" {
+ name.span()
+ .unwrap()
+ .warning("come on, pick a more creative name")
+ .emit();
+ }
+
+ // The error looks like this.
+ //
+ // error: I can't think of a legitimate use for lazily initializing the value `()`
+ // --> src/main.rs:10:27
+ // |
+ // 10 | static ref UNIT: () = ();
+ // | ^^
+ if let Expr::Tuple(ref init) = init {
+ if init.elems.is_empty() {
+ init.span()
+ .unwrap()
+ .error("I can't think of a legitimate use for lazily initializing the value `()`")
+ .emit();
+ return TokenStream::new();
+ }
+ }
+
+ // Assert that the static type implements Sync. If not, user sees an error
+ // message like the following. We span this assertion with the field type's
+ // line/column so that the error message appears in the correct place.
+ //
+ // error[E0277]: the trait bound `*const (): std::marker::Sync` is not satisfied
+ // --> src/main.rs:10:21
+ // |
+ // 10 | static ref PTR: *const () = &();
+ // | ^^^^^^^^^ `*const ()` cannot be shared between threads safely
+ let assert_sync = quote_spanned! {ty.span()=>
+ struct _AssertSync where #ty: std::marker::Sync;
+ };
+
+ // Check for Sized. Not vital to check here, but the error message is less
+ // confusing this way than if they get a Sized error in one of our
+ // implementation details where it assumes Sized.
+ //
+ // error[E0277]: the trait bound `str: std::marker::Sized` is not satisfied
+ // --> src/main.rs:10:19
+ // |
+ // 10 | static ref A: str = "";
+ // | ^^^ `str` does not have a constant size known at compile-time
+ let assert_sized = quote_spanned! {ty.span()=>
+ struct _AssertSized where #ty: std::marker::Sized;
+ };
+
+ let init_ptr = quote_spanned! {init.span()=>
+ Box::into_raw(Box::new(#init))
+ };
+
+ let expanded = quote! {
+ #visibility struct #name;
+
+ impl std::ops::Deref for #name {
+ type Target = #ty;
+
+ fn deref(&self) -> &#ty {
+ #assert_sync
+ #assert_sized
+
+ static ONCE: std::sync::Once = std::sync::Once::new();
+ static mut VALUE: *mut #ty = 0 as *mut #ty;
+
+ unsafe {
+ ONCE.call_once(|| VALUE = #init_ptr);
+ &*VALUE
+ }
+ }
+ }
+ };
+
+ TokenStream::from(expanded)
+}
generated by cgit v1.2.3 (git 2.46.0) at 2025-10-31 17:53:29 +0000