rustc_target: Refactor linker flavor inference

Go through an intermediate pair of `cc`and `lld` hints instead of mapping CLI options to `LinkerFlavor` directly, and use the target's default linker flavor as a reference.

Author: petrochenkov

compiler/rustc_codegen_ssa/src/back/link.rs

@@ -23,7 +23,7 @@ use rustc_session::utils::NativeLibKind;
 use rustc_session::{filesearch, Session};
 use rustc_span::symbol::Symbol;
 use rustc_target::spec::crt_objects::{CrtObjects, LinkSelfContainedDefault};
-use rustc_target::spec::{Cc, LinkOutputKind, LinkerFlavor, LinkerFlavorCli, Lld, PanicStrategy};
+use rustc_target::spec::{Cc, LinkOutputKind, LinkerFlavor, Lld, PanicStrategy};
 use rustc_target::spec::{RelocModel, RelroLevel, SanitizerSet, SplitDebuginfo};
 
 use super::archive::{ArchiveBuilder, ArchiveBuilderBuilder};
@@ -1302,44 +1302,7 @@ pub fn linker_and_flavor(sess: &Session) -> (PathBuf, LinkerFlavor) {
                 let stem = linker.file_stem().and_then(|stem| stem.to_str()).unwrap_or_else(|| {
                     sess.emit_fatal(errors::LinkerFileStem);
                 });
-
-                // Remove any version postfix.
-                let stem = stem
-                    .rsplit_once('-')
-                    .and_then(|(lhs, rhs)| rhs.chars().all(char::is_numeric).then_some(lhs))
-                    .unwrap_or(stem);
-
-                // GCC/Clang can have an optional target prefix.
-                let flavor = if stem == "emcc" {
-                    LinkerFlavor::EmCc
-                } else if stem == "gcc"
-                    || stem.ends_with("-gcc")
-                    || stem == "g++"
-                    || stem.ends_with("-g++")
-                    || stem == "clang"
-                    || stem.ends_with("-clang")
-                    || stem == "clang++"
-                    || stem.ends_with("-clang++")
-                {
-                    LinkerFlavor::from_cli(LinkerFlavorCli::Gcc, &sess.target)
-                } else if stem == "wasm-ld" || stem.ends_with("-wasm-ld") {
-                    LinkerFlavor::WasmLld(Cc::No)
-                } else if stem == "ld" || stem.ends_with("-ld") {
-                    LinkerFlavor::from_cli(LinkerFlavorCli::Ld, &sess.target)
-                } else if stem == "ld.lld" {
-                    LinkerFlavor::Gnu(Cc::No, Lld::Yes)
-                } else if stem == "link" {
-                    LinkerFlavor::Msvc(Lld::No)
-                } else if stem == "lld-link" {
-                    LinkerFlavor::Msvc(Lld::Yes)
-                } else if stem == "lld" || stem == "rust-lld" {
-                    let lld_flavor = sess.target.linker_flavor.lld_flavor();
-                    LinkerFlavor::from_cli(LinkerFlavorCli::Lld(lld_flavor), &sess.target)
-                } else {
-                    // fall back to the value in the target spec
-                    sess.target.linker_flavor
-                };
-
+                let flavor = sess.target.linker_flavor.with_linker_hints(stem);
                 Some((linker, flavor))
             }
             (None, None) => None,
@@ -1349,7 +1312,7 @@ pub fn linker_and_flavor(sess: &Session) -> (PathBuf, LinkerFlavor) {
     // linker and linker flavor specified via command line have precedence over what the target
     // specification specifies
     let linker_flavor =
-        sess.opts.cg.linker_flavor.map(|flavor| LinkerFlavor::from_cli(flavor, &sess.target));
+        sess.opts.cg.linker_flavor.map(|flavor| sess.target.linker_flavor.with_cli_hints(flavor));
     if let Some(ret) = infer_from(sess, sess.opts.cg.linker.clone(), linker_flavor) {
         return ret;
     }

compiler/rustc_target/src/spec/mod.rs

@@ -205,15 +205,11 @@ impl ToJson for LldFlavor {
 }
 
 impl LinkerFlavor {
-    pub fn from_cli(cli: LinkerFlavorCli, target: &TargetOptions) -> LinkerFlavor {
-        Self::from_cli_impl(cli, target.linker_flavor.lld_flavor(), target.linker_flavor.is_gnu())
-    }
-
-    /// The passed CLI flavor is preferred over other args coming from the default target spec,
-    /// so this function can produce a flavor that is incompatible with the current target.
-    /// FIXME: Produce errors when `-Clinker-flavor` is set to something incompatible
-    /// with the current target.
-    fn from_cli_impl(cli: LinkerFlavorCli, lld_flavor: LldFlavor, is_gnu: bool) -> LinkerFlavor {
+    /// At this point the target's reference linker flavor doesn't yet exist and we need to infer
+    /// it. The inference always succeds and gives some result, and we don't report any flavor
+    /// incompatibility errors for json target specs. The CLI flavor is used as the main source
+    /// of truth, other flags are used in case of ambiguities.
+    fn from_cli_json(cli: LinkerFlavorCli, lld_flavor: LldFlavor, is_gnu: bool) -> LinkerFlavor {
         match cli {
             LinkerFlavorCli::Gcc => match lld_flavor {
                 LldFlavor::Ld if is_gnu => LinkerFlavor::Gnu(Cc::Yes, Lld::No),
@@ -257,6 +253,72 @@ impl LinkerFlavor {
         }
     }
 
+    fn infer_cli_hints(cli: LinkerFlavorCli) -> (Option<Cc>, Option<Lld>) {
+        match cli {
+            LinkerFlavorCli::Gcc | LinkerFlavorCli::Em => (Some(Cc::Yes), None),
+            LinkerFlavorCli::Lld(_) => (Some(Cc::No), Some(Lld::Yes)),
+            LinkerFlavorCli::Ld | LinkerFlavorCli::Msvc => (Some(Cc::No), Some(Lld::No)),
+            LinkerFlavorCli::BpfLinker | LinkerFlavorCli::PtxLinker => (None, None),
+        }
+    }
+
+    fn infer_linker_hints(linker_stem: &str) -> (Option<Cc>, Option<Lld>) {
+        // Remove any version postfix.
+        let stem = linker_stem
+            .rsplit_once('-')
+            .and_then(|(lhs, rhs)| rhs.chars().all(char::is_numeric).then_some(lhs))
+            .unwrap_or(linker_stem);
+
+        // GCC/Clang can have an optional target prefix.
+        if stem == "emcc"
+            || stem == "gcc"
+            || stem.ends_with("-gcc")
+            || stem == "g++"
+            || stem.ends_with("-g++")
+            || stem == "clang"
+            || stem.ends_with("-clang")
+            || stem == "clang++"
+            || stem.ends_with("-clang++")
+        {
+            (Some(Cc::Yes), None)
+        } else if stem == "wasm-ld"
+            || stem.ends_with("-wasm-ld")
+            || stem == "ld.lld"
+            || stem == "lld"
+            || stem == "rust-lld"
+            || stem == "lld-link"
+        {
+            (Some(Cc::No), Some(Lld::Yes))
+        } else if stem == "ld" || stem.ends_with("-ld") || stem == "link" {
+            (Some(Cc::No), Some(Lld::No))
+        } else {
+            (None, None)
+        }
+    }
+
+    fn with_hints(self, (cc_hint, lld_hint): (Option<Cc>, Option<Lld>)) -> LinkerFlavor {
+        match self {
+            LinkerFlavor::Gnu(cc, lld) => {
+                LinkerFlavor::Gnu(cc_hint.unwrap_or(cc), lld_hint.unwrap_or(lld))
+            }
+            LinkerFlavor::Darwin(cc, lld) => {
+                LinkerFlavor::Darwin(cc_hint.unwrap_or(cc), lld_hint.unwrap_or(lld))
+            }
+            LinkerFlavor::WasmLld(cc) => LinkerFlavor::WasmLld(cc_hint.unwrap_or(cc)),
+            LinkerFlavor::Unix(cc) => LinkerFlavor::Unix(cc_hint.unwrap_or(cc)),
+            LinkerFlavor::Msvc(lld) => LinkerFlavor::Msvc(lld_hint.unwrap_or(lld)),
+            LinkerFlavor::EmCc | LinkerFlavor::Bpf | LinkerFlavor::Ptx => self,
+        }
+    }
+
+    pub fn with_cli_hints(self, cli: LinkerFlavorCli) -> LinkerFlavor {
+        self.with_hints(LinkerFlavor::infer_cli_hints(cli))
+    }
+
+    pub fn with_linker_hints(self, linker_stem: &str) -> LinkerFlavor {
+        self.with_hints(LinkerFlavor::infer_linker_hints(linker_stem))
+    }
+
     pub fn lld_flavor(self) -> LldFlavor {
         match self {
             LinkerFlavor::Gnu(..)
@@ -1801,7 +1863,7 @@ impl TargetOptions {
     }
 
     fn update_from_cli(&mut self) {
-        self.linker_flavor = LinkerFlavor::from_cli_impl(
+        self.linker_flavor = LinkerFlavor::from_cli_json(
             self.linker_flavor_json,
             self.lld_flavor_json,
             self.linker_is_gnu_json,
@@ -1815,12 +1877,7 @@ impl TargetOptions {
         ] {
             args.clear();
             for (flavor, args_json) in args_json {
-                // Cannot use `from_cli` due to borrow checker.
-                let linker_flavor = LinkerFlavor::from_cli_impl(
-                    *flavor,
-                    self.lld_flavor_json,
-                    self.linker_is_gnu_json,
-                );
+                let linker_flavor = self.linker_flavor.with_cli_hints(*flavor);
                 // Normalize to no lld to avoid asserts.
                 let linker_flavor = match linker_flavor {
                     LinkerFlavor::Gnu(cc, _) => LinkerFlavor::Gnu(cc, Lld::No),