1 // rustc-cfg emitted by the build script:
2 //
3 // "use_proc_macro"
4 // Link to extern crate proc_macro. Available on any compiler and any target
5 // except wasm32. Requires "proc-macro" Cargo cfg to be enabled (default is
6 // enabled). On wasm32 we never link to proc_macro even if "proc-macro" cfg
7 // is enabled.
8 //
9 // "wrap_proc_macro"
10 // Wrap types from libproc_macro rather than polyfilling the whole API.
11 // Enabled on rustc 1.29+ as long as procmacro2_semver_exempt is not set,
12 // because we can't emulate the unstable API without emulating everything
13 // else. Also enabled unconditionally on nightly, in which case the
14 // procmacro2_semver_exempt surface area is implemented by using the
15 // nightly-only proc_macro API.
16 //
17 // "proc_macro_span"
18 // Enable non-dummy behavior of Span::start and Span::end methods which
19 // requires an unstable compiler feature. Enabled when building with
20 // nightly, unless `-Z allow-feature` in RUSTFLAGS disallows unstable
21 // features.
22 //
23 // "super_unstable"
24 // Implement the semver exempt API in terms of the nightly-only proc_macro
25 // API. Enabled when using procmacro2_semver_exempt on a nightly compiler.
26 //
27 // "span_locations"
28 // Provide methods Span::start and Span::end which give the line/column
29 // location of a token. Enabled by procmacro2_semver_exempt or the
30 // "span-locations" Cargo cfg. This is behind a cfg because tracking
31 // location inside spans is a performance hit.
32
33 use std::env;
34 use std::process::{self, Command};
35 use std::str;
36
main()37 fn main() {
38 println!("cargo:rerun-if-changed=build.rs");
39
40 let version = match rustc_version() {
41 Some(version) => version,
42 None => return,
43 };
44
45 if version.minor < 31 {
46 eprintln!("Minimum supported rustc version is 1.31");
47 process::exit(1);
48 }
49
50 let semver_exempt = cfg!(procmacro2_semver_exempt);
51 if semver_exempt {
52 // https://github.com/alexcrichton/proc-macro2/issues/147
53 println!("cargo:rustc-cfg=procmacro2_semver_exempt");
54 }
55
56 if semver_exempt || cfg!(feature = "span-locations") {
57 println!("cargo:rustc-cfg=span_locations");
58 }
59
60 let target = env::var("TARGET").unwrap();
61 if !enable_use_proc_macro(&target) {
62 return;
63 }
64
65 println!("cargo:rustc-cfg=use_proc_macro");
66
67 if version.nightly || !semver_exempt {
68 println!("cargo:rustc-cfg=wrap_proc_macro");
69 }
70
71 if version.nightly && feature_allowed("proc_macro_span") {
72 println!("cargo:rustc-cfg=proc_macro_span");
73 }
74
75 if semver_exempt && version.nightly {
76 println!("cargo:rustc-cfg=super_unstable");
77 }
78 }
79
enable_use_proc_macro(target: &str) -> bool80 fn enable_use_proc_macro(target: &str) -> bool {
81 // wasm targets don't have the `proc_macro` crate, disable this feature.
82 if target.contains("wasm32") {
83 return false;
84 }
85
86 // Otherwise, only enable it if our feature is actually enabled.
87 cfg!(feature = "proc-macro")
88 }
89
90 struct RustcVersion {
91 minor: u32,
92 nightly: bool,
93 }
94
rustc_version() -> Option<RustcVersion>95 fn rustc_version() -> Option<RustcVersion> {
96 let rustc = env::var_os("RUSTC")?;
97 let output = Command::new(rustc).arg("--version").output().ok()?;
98 let version = str::from_utf8(&output.stdout).ok()?;
99 let nightly = version.contains("nightly") || version.contains("dev");
100 let mut pieces = version.split('.');
101 if pieces.next() != Some("rustc 1") {
102 return None;
103 }
104 let minor = pieces.next()?.parse().ok()?;
105 Some(RustcVersion { minor, nightly })
106 }
107
feature_allowed(feature: &str) -> bool108 fn feature_allowed(feature: &str) -> bool {
109 // Recognized formats:
110 //
111 // -Z allow-features=feature1,feature2
112 //
113 // -Zallow-features=feature1,feature2
114
115 if let Some(rustflags) = env::var_os("RUSTFLAGS") {
116 for mut flag in rustflags.to_string_lossy().split(' ') {
117 if flag.starts_with("-Z") {
118 flag = &flag["-Z".len()..];
119 }
120 if flag.starts_with("allow-features=") {
121 flag = &flag["allow-features=".len()..];
122 return flag.split(',').any(|allowed| allowed == feature);
123 }
124 }
125 }
126
127 // No allow-features= flag, allowed by default.
128 true
129 }
130