1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
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
}
|
