Implement cfg(target_abi) (RFC 2992)

Add an `abi` field to `TargetOptions`, defaulting to "". Support using
`cfg(target_abi = "...")` for conditional compilation on that field.

Gated by `feature(cfg_target_abi)`.

Add a test for `target_abi`, and a test for the feature gate.

Add `target_abi` to tidy as a platform-specific cfg.

This does not add an abi to any existing target.

Author: joshtriplett

compiler/rustc_feature/src/active.rs

@@ -687,6 +687,9 @@ declare_features! (
     /// Allows qualified paths in struct expressions, struct patterns and tuple struct patterns.
     (active, more_qualified_paths, "1.54.0", Some(80080), None),
 
+    /// Allows `cfg(target_abi = "...")`.
+    (active, cfg_target_abi, "1.55.0", Some(80970), None),
+
     // -------------------------------------------------------------------------
     // feature-group-end: actual feature gates
     // -------------------------------------------------------------------------

compiler/rustc_feature/src/builtin_attrs.rs

@@ -23,6 +23,7 @@ pub type GatedCfg = (Symbol, Symbol, GateFn);
 /// `cfg(...)`'s that are feature gated.
 const GATED_CFGS: &[GatedCfg] = &[
     // (name in cfg, feature, function to check if the feature is enabled)
+    (sym::target_abi, sym::cfg_target_abi, cfg_fn!(cfg_target_abi)),
     (sym::target_thread_local, sym::cfg_target_thread_local, cfg_fn!(cfg_target_thread_local)),
     (sym::target_has_atomic, sym::cfg_target_has_atomic, cfg_fn!(cfg_target_has_atomic)),
     (sym::target_has_atomic_load_store, sym::cfg_target_has_atomic, cfg_fn!(cfg_target_has_atomic)),

compiler/rustc_session/src/config.rs

@@ -805,6 +805,7 @@ fn default_configuration(sess: &Session) -> CrateConfig {
     let wordsz = sess.target.pointer_width.to_string();
     let os = &sess.target.os;
     let env = &sess.target.env;
+    let abi = &sess.target.abi;
     let vendor = &sess.target.vendor;
     let min_atomic_width = sess.target.min_atomic_width();
     let max_atomic_width = sess.target.max_atomic_width();
@@ -814,7 +815,7 @@ fn default_configuration(sess: &Session) -> CrateConfig {
     });
 
     let mut ret = FxHashSet::default();
-    ret.reserve(6); // the minimum number of insertions
+    ret.reserve(7); // the minimum number of insertions
     // Target bindings.
     ret.insert((sym::target_os, Some(Symbol::intern(os))));
     for fam in &sess.target.families {
@@ -829,6 +830,7 @@ fn default_configuration(sess: &Session) -> CrateConfig {
     ret.insert((sym::target_endian, Some(Symbol::intern(end.as_str()))));
     ret.insert((sym::target_pointer_width, Some(Symbol::intern(&wordsz))));
     ret.insert((sym::target_env, Some(Symbol::intern(env))));
+    ret.insert((sym::target_abi, Some(Symbol::intern(abi))));
     ret.insert((sym::target_vendor, Some(Symbol::intern(vendor))));
     if sess.target.has_elf_tls {
         ret.insert((sym::target_thread_local, None));

compiler/rustc_span/src/symbol.rs

@@ -353,6 +353,7 @@ symbols! {
         cfg_eval,
         cfg_panic,
         cfg_sanitize,
+        cfg_target_abi,
         cfg_target_feature,
         cfg_target_has_atomic,
         cfg_target_thread_local,
@@ -1199,6 +1200,7 @@ symbols! {
         sync,
         sync_trait,
         t32,
+        target_abi,
         target_arch,
         target_endian,
         target_env,

compiler/rustc_target/src/spec/mod.rs

@@ -1025,6 +1025,9 @@ pub struct TargetOptions {
     pub os: String,
     /// Environment name to use for conditional compilation (`target_env`). Defaults to "".
     pub env: String,
+    /// ABI name to distinguish multiple ABIs on the same OS and architecture. For instance, `"eabi"`
+    /// or `"eabihf"`. Defaults to "".
+    pub abi: String,
     /// Vendor name to use for conditional compilation (`target_vendor`). Defaults to "unknown".
     pub vendor: String,
     /// Default linker flavor used if `-C linker-flavor` or `-C linker` are not passed
@@ -1342,6 +1345,7 @@ impl Default for TargetOptions {
             c_int_width: "32".to_string(),
             os: "none".to_string(),
             env: String::new(),
+            abi: String::new(),
             vendor: "unknown".to_string(),
             linker_flavor: LinkerFlavor::Gcc,
             linker: option_env!("CFG_DEFAULT_LINKER").map(|s| s.to_string()),
@@ -1919,6 +1923,7 @@ impl Target {
         key!(c_int_width = "target-c-int-width");
         key!(os);
         key!(env);
+        key!(abi);
         key!(vendor);
         key!(linker_flavor, LinkerFlavor)?;
         key!(linker, optional);
@@ -2152,6 +2157,7 @@ impl ToJson for Target {
         target_option_val!(c_int_width, "target-c-int-width");
         target_option_val!(os);
         target_option_val!(env);
+        target_option_val!(abi);
         target_option_val!(vendor);
         target_option_val!(linker_flavor);
         target_option_val!(linker);

src/test/ui/cfg/cfg-target-abi.rs

@@ -0,0 +1,10 @@
+// run-pass
+#![feature(cfg_target_abi)]
+
+#[cfg(target_abi = "eabihf")]
+pub fn main() {
+}
+
+#[cfg(not(target_abi = "eabihf"))]
+pub fn main() {
+}

src/test/ui/feature-gates/feature-gate-cfg-target-abi.rs

@@ -0,0 +1,11 @@
+#[cfg(target_abi = "x")] //~ ERROR `cfg(target_abi)` is experimental
+#[cfg_attr(target_abi = "x", x)] //~ ERROR `cfg(target_abi)` is experimental
+struct Foo(u64, u64);
+
+#[cfg(not(any(all(target_abi = "x"))))] //~ ERROR `cfg(target_abi)` is experimental
+fn foo() {}
+
+fn main() {
+    cfg!(target_abi = "x");
+    //~^ ERROR `cfg(target_abi)` is experimental and subject to change
+}

src/test/ui/feature-gates/feature-gate-cfg-target-abi.stderr

@@ -0,0 +1,39 @@
+error[E0658]: `cfg(target_abi)` is experimental and subject to change
+  --> $DIR/feature-gate-cfg-target-abi.rs:2:12
+   |
+LL | #[cfg_attr(target_abi = "x", x)]
+   |            ^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #80970 <https://github.com/rust-lang/rust/issues/80970> for more information
+   = help: add `#![feature(cfg_target_abi)]` to the crate attributes to enable
+
+error[E0658]: `cfg(target_abi)` is experimental and subject to change
+  --> $DIR/feature-gate-cfg-target-abi.rs:1:7
+   |
+LL | #[cfg(target_abi = "x")]
+   |       ^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #80970 <https://github.com/rust-lang/rust/issues/80970> for more information
+   = help: add `#![feature(cfg_target_abi)]` to the crate attributes to enable
+
+error[E0658]: `cfg(target_abi)` is experimental and subject to change
+  --> $DIR/feature-gate-cfg-target-abi.rs:5:19
+   |
+LL | #[cfg(not(any(all(target_abi = "x"))))]
+   |                   ^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #80970 <https://github.com/rust-lang/rust/issues/80970> for more information
+   = help: add `#![feature(cfg_target_abi)]` to the crate attributes to enable
+
+error[E0658]: `cfg(target_abi)` is experimental and subject to change
+  --> $DIR/feature-gate-cfg-target-abi.rs:9:10
+   |
+LL |     cfg!(target_abi = "x");
+   |          ^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #80970 <https://github.com/rust-lang/rust/issues/80970> for more information
+   = help: add `#![feature(cfg_target_abi)]` to the crate attributes to enable
+
+error: aborting due to 4 previous errors
+
+For more information about this error, try `rustc --explain E0658`.

src/tools/tidy/src/pal.rs

@@ -122,6 +122,7 @@ fn check_cfgs(
 
         let contains_platform_specific_cfg = cfg.contains("target_os")
             || cfg.contains("target_env")
+            || cfg.contains("target_abi")
             || cfg.contains("target_vendor")
             || cfg.contains("unix")
             || cfg.contains("windows");