1 files changed, 129 insertions, 0 deletions
diff --git a/proc-macro2/build.rs b/proc-macro2/build.rs
new file mode 100644
index 0000000..deb9b92
--- /dev/null
+++ b/proc-macro2/build.rs
@@ -0,0 +1,129 @@
+// rustc-cfg emitted by the build script:
+//
+// "use_proc_macro"
+//     Link to extern crate proc_macro. Available on any compiler and any target
+//     except wasm32. Requires "proc-macro" Cargo cfg to be enabled (default is
+//     enabled). On wasm32 we never link to proc_macro even if "proc-macro" cfg
+//     is enabled.
+//
+// "wrap_proc_macro"
+//     Wrap types from libproc_macro rather than polyfilling the whole API.
+//     Enabled on rustc 1.29+ as long as procmacro2_semver_exempt is not set,
+//     because we can't emulate the unstable API without emulating everything
+//     else. Also enabled unconditionally on nightly, in which case the
+//     procmacro2_semver_exempt surface area is implemented by using the
+//     nightly-only proc_macro API.
+//
+// "proc_macro_span"
+//     Enable non-dummy behavior of Span::start and Span::end methods which
+//     requires an unstable compiler feature. Enabled when building with
+//     nightly, unless `-Z allow-feature` in RUSTFLAGS disallows unstable
+//     features.
+//
+// "super_unstable"
+//     Implement the semver exempt API in terms of the nightly-only proc_macro
+//     API. Enabled when using procmacro2_semver_exempt on a nightly compiler.
+//
+// "span_locations"
+//     Provide methods Span::start and Span::end which give the line/column
+//     location of a token. Enabled by procmacro2_semver_exempt or the
+//     "span-locations" Cargo cfg. This is behind a cfg because tracking
+//     location inside spans is a performance hit.
+
+use std::env;
+use std::process::{self, Command};
+use std::str;
+
+fn main() {
+    println!("cargo:rerun-if-changed=build.rs");
+
+    let version = match rustc_version() {
+        Some(version) => version,
+        None => return,
+    };
+
+    if version.minor < 31 {
+        eprintln!("Minimum supported rustc version is 1.31");
+        process::exit(1);
+    }
+
+    let semver_exempt = cfg!(procmacro2_semver_exempt);
+    if semver_exempt {
+        // https://github.com/alexcrichton/proc-macro2/issues/147
+        println!("cargo:rustc-cfg=procmacro2_semver_exempt");
+    }
+
+    if semver_exempt || cfg!(feature = "span-locations") {
+        println!("cargo:rustc-cfg=span_locations");
+    }
+
+    let target = env::var("TARGET").unwrap();
+    if !enable_use_proc_macro(&target) {
+        return;
+    }
+
+    println!("cargo:rustc-cfg=use_proc_macro");
+
+    if version.nightly || !semver_exempt {
+        println!("cargo:rustc-cfg=wrap_proc_macro");
+    }
+
+    if version.nightly && feature_allowed("proc_macro_span") {
+        println!("cargo:rustc-cfg=proc_macro_span");
+    }
+
+    if semver_exempt && version.nightly {
+        println!("cargo:rustc-cfg=super_unstable");
+    }
+}
+
+fn enable_use_proc_macro(target: &str) -> bool {
+    // wasm targets don't have the `proc_macro` crate, disable this feature.
+    if target.contains("wasm32") {
+        return false;
+    }
+
+    // Otherwise, only enable it if our feature is actually enabled.
+    cfg!(feature = "proc-macro")
+}
+
+struct RustcVersion {
+    minor: u32,
+    nightly: bool,
+}
+
+fn rustc_version() -> Option<RustcVersion> {
+    let rustc = env::var_os("RUSTC")?;
+    let output = Command::new(rustc).arg("--version").output().ok()?;
+    let version = str::from_utf8(&output.stdout).ok()?;
+    let nightly = version.contains("nightly") || version.contains("dev");
+    let mut pieces = version.split('.');
+    if pieces.next() != Some("rustc 1") {
+        return None;
+    }
+    let minor = pieces.next()?.parse().ok()?;
+    Some(RustcVersion { minor, nightly })
+}
+
+fn feature_allowed(feature: &str) -> bool {
+    // Recognized formats:
+    //
+    //     -Z allow-features=feature1,feature2
+    //
+    //     -Zallow-features=feature1,feature2
+
+    if let Some(rustflags) = env::var_os("RUSTFLAGS") {
+        for mut flag in rustflags.to_string_lossy().split(' ') {
+            if flag.starts_with("-Z") {
+                flag = &flag["-Z".len()..];
+            }
+            if flag.starts_with("allow-features=") {
+                flag = &flag["allow-features=".len()..];
+                return flag.split(',').any(|allowed| allowed == feature);
+            }
+        }
+    }
+
+    // No allow-features= flag, allowed by default.
+    true
+}