Add structopt dependency in version 0.3.7

This patch series replaces argparse with structopt in the argument
handling code. As a first step, we need structopt as a dependency.

Import subrepo structopt/:structopt at efbdda4753592e27bc430fb01f7b9650b2f3174d
Import subrepo bitflags/:bitflags at 30668016aca6bd3b02c766e8347e0b4080d4c296
Import subrepo clap/:clap at 784524f7eb193e35f81082cc69454c8c21b948f7
Import subrepo heck/:heck at 093d56fbf001e1506e56dbfa38631d99b1066df1
Import subrepo proc-macro-error/:proc-macro-error at 6c4cfe79a622c5de8ae68557993542be46eacae2
Import subrepo proc-macro2/:proc-macro2 at d5d48eddca4566e5438e8a2cbed4a74e049544de
Import subrepo quote/:quote at 727436c6c137b20f0f34dde5d8fda2679b9747ad
Import subrepo rustversion/:rustversion at 0c5663313516263059ce9059ef81fc7a1cf655ca
Import subrepo syn-mid/:syn-mid at 5d3d85414a9e6674e1857ec22a87b96e04a6851a
Import subrepo syn/:syn at e87c27e87f6f4ef8919d0372bdb056d53ef0d8f3
Import subrepo textwrap/:textwrap at abcd618beae3f74841032aa5b53c1086b0a57ca2
Import subrepo unicode-segmentation/:unicode-segmentation at 637c9874c4fe0c205ff27787faf150a40295c6c3
Import subrepo unicode-width/:unicode-width at 3033826f8bf05e82724140a981d5941e48fce393
Import subrepo unicode-xid/:unicode-xid at 4baae9fffb156ba229665b972a9cd5991787ceb7

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)
+}