Auto merge of #78951 - petrochenkov:unknown, r=ehuss

rustc_target: Change os and vendor values to "none" and "unknown" for some targets

Closes https://github.com/rust-lang/rust/issues/77730
r? `@ehuss`

compiler/rustc_target/src/spec/aarch64_unknown_none.rs

@@ -10,7 +10,6 @@ use super::{LinkerFlavor, LldFlavor, PanicStrategy, RelocModel, Target, TargetOp
 
 pub fn target() -> Target {
     let opts = TargetOptions {
-        vendor: String::new(),
         linker_flavor: LinkerFlavor::Lld(LldFlavor::Ld),
         linker: Some("rust-lld".to_owned()),
         features: "+strict-align,+neon,+fp-armv8".to_string(),

compiler/rustc_target/src/spec/aarch64_unknown_none_softfloat.rs

@@ -10,7 +10,6 @@ use super::{LinkerFlavor, LldFlavor, PanicStrategy, RelocModel, Target, TargetOp
 
 pub fn target() -> Target {
     let opts = TargetOptions {
-        vendor: String::new(),
         linker_flavor: LinkerFlavor::Lld(LldFlavor::Ld),
         linker: Some("rust-lld".to_owned()),
         features: "+strict-align,-neon,-fp-armv8".to_string(),

compiler/rustc_target/src/spec/armebv7r_none_eabi.rs

@@ -12,7 +12,6 @@ pub fn target() -> Target {
 
         options: TargetOptions {
             endian: "big".to_string(),
-            vendor: String::new(),
             linker_flavor: LinkerFlavor::Lld(LldFlavor::Ld),
             executables: true,
             linker: Some("rust-lld".to_owned()),

compiler/rustc_target/src/spec/armebv7r_none_eabihf.rs

@@ -12,7 +12,6 @@ pub fn target() -> Target {
 
         options: TargetOptions {
             endian: "big".to_string(),
-            vendor: String::new(),
             linker_flavor: LinkerFlavor::Lld(LldFlavor::Ld),
             executables: true,
             linker: Some("rust-lld".to_owned()),

compiler/rustc_target/src/spec/armv7a_none_eabi.rs

@@ -10,9 +10,6 @@
 // bare-metal binaries (the `gcc` linker has the advantage that it knows where C
 // libraries and crt*.o are but it's not much of an advantage here); LLD is also
 // faster
-// - `os` set to `none`. rationale: matches `thumb` targets
-// - `env` and `vendor` are set to an empty string. rationale: matches `thumb`
-// targets
 // - `panic_strategy` set to `abort`. rationale: matches `thumb` targets
 // - `relocation-model` set to `static`; also no PIE, no relro and no dynamic
 // linking. rationale: matches `thumb` targets
@@ -21,7 +18,6 @@ use super::{LinkerFlavor, LldFlavor, PanicStrategy, RelocModel, Target, TargetOp
 
 pub fn target() -> Target {
     let opts = TargetOptions {
-        vendor: String::new(),
         linker_flavor: LinkerFlavor::Lld(LldFlavor::Ld),
         linker: Some("rust-lld".to_owned()),
         features: "+v7,+thumb2,+soft-float,-neon,+strict-align".to_string(),

compiler/rustc_target/src/spec/armv7a_none_eabihf.rs

@@ -9,7 +9,6 @@ use super::{LinkerFlavor, LldFlavor, PanicStrategy, RelocModel, Target, TargetOp
 
 pub fn target() -> Target {
     let opts = TargetOptions {
-        vendor: String::new(),
         linker_flavor: LinkerFlavor::Lld(LldFlavor::Ld),
         linker: Some("rust-lld".to_owned()),
         features: "+v7,+vfp3,-d32,+thumb2,-neon,+strict-align".to_string(),

compiler/rustc_target/src/spec/armv7r_none_eabi.rs

@@ -11,7 +11,6 @@ pub fn target() -> Target {
         arch: "arm".to_string(),
 
         options: TargetOptions {
-            vendor: String::new(),
             linker_flavor: LinkerFlavor::Lld(LldFlavor::Ld),
             executables: true,
             linker: Some("rust-lld".to_owned()),

compiler/rustc_target/src/spec/armv7r_none_eabihf.rs

@@ -11,7 +11,6 @@ pub fn target() -> Target {
         arch: "arm".to_string(),
 
         options: TargetOptions {
-            vendor: String::new(),
             linker_flavor: LinkerFlavor::Lld(LldFlavor::Ld),
             executables: true,
             linker: Some("rust-lld".to_owned()),

compiler/rustc_target/src/spec/avr_gnu_base.rs

@@ -11,7 +11,6 @@ pub fn target(target_cpu: String) -> Target {
         pointer_width: 16,
         options: TargetOptions {
             c_int_width: "16".to_string(),
-            os: "unknown".to_string(),
             cpu: target_cpu.clone(),
             exe_suffix: ".elf".to_string(),
 

compiler/rustc_target/src/spec/fuchsia_base.rs

@@ -21,7 +21,6 @@ pub fn opts() -> TargetOptions {
 
     TargetOptions {
         os: "fuchsia".to_string(),
-        vendor: String::new(),
         linker_flavor: LinkerFlavor::Lld(LldFlavor::Ld),
         linker: Some("rust-lld".to_owned()),
         lld_flavor: LldFlavor::Ld,

compiler/rustc_target/src/spec/mipsel_unknown_none.rs

@@ -14,7 +14,6 @@ pub fn target() -> Target {
         arch: "mips".to_string(),
 
         options: TargetOptions {
-            vendor: String::new(),
             linker_flavor: LinkerFlavor::Lld(LldFlavor::Ld),
             cpu: "mips32r2".to_string(),
             features: "+mips32r2,+soft-float,+noabicalls".to_string(),

compiler/rustc_target/src/spec/mod.rs

@@ -713,11 +713,14 @@ pub struct TargetOptions {
     pub endian: String,
     /// Width of c_int type. Defaults to "32".
     pub c_int_width: String,
-    /// OS name to use for conditional compilation. Defaults to "none".
+    /// OS name to use for conditional compilation (`target_os`). Defaults to "none".
+    /// "none" implies a bare metal target without `std` library.
+    /// A couple of targets having `std` also use "unknown" as an `os` value,
+    /// but they are exceptions.
     pub os: String,
-    /// Environment name to use for conditional compilation. Defaults to "".
+    /// Environment name to use for conditional compilation (`target_env`). Defaults to "".
     pub env: String,
-    /// Vendor name to use for conditional compilation. Defaults to "unknown".
+    /// 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
     /// on the command line. Defaults to `LinkerFlavor::Gcc`.

compiler/rustc_target/src/spec/msp430_none_elf.rs

@@ -9,7 +9,6 @@ pub fn target() -> Target {
 
         options: TargetOptions {
             c_int_width: "16".to_string(),
-            vendor: String::new(),
             executables: true,
 
             // The LLVM backend currently can't generate object files. To

compiler/rustc_target/src/spec/tests/tests_impl.rs

@@ -36,5 +36,18 @@ impl Target {
                 && self.post_link_objects_fallback.is_empty())
                 || self.crt_objects_fallback.is_some()
         );
+        // Keep the default "unknown" vendor instead.
+        assert_ne!(self.vendor, "");
+        if !self.can_use_os_unknown() {
+            // Keep the default "none" for bare metal targets instead.
+            assert_ne!(self.os, "unknown");
+        }
+    }
+
+    // Add your target to the whitelist if it has `std` library
+    // and you certainly want "unknown" for the OS name.
+    fn can_use_os_unknown(&self) -> bool {
+        self.llvm_target == "wasm32-unknown-unknown"
+            || (self.env == "sgx" && self.vendor == "fortanix")
     }
 }

compiler/rustc_target/src/spec/thumb_base.rs

@@ -32,7 +32,6 @@ use crate::spec::{LinkerFlavor, LldFlavor, PanicStrategy, RelocModel, TargetOpti
 pub fn opts() -> TargetOptions {
     // See rust-lang/rfcs#1645 for a discussion about these defaults
     TargetOptions {
-        vendor: String::new(),
         linker_flavor: LinkerFlavor::Lld(LldFlavor::Ld),
         executables: true,
         // In most cases, LLD is good enough

compiler/rustc_target/src/spec/wasm32_wasi.rs

@@ -79,7 +79,6 @@ pub fn target() -> Target {
     let mut options = wasm32_base::options();
 
     options.os = "wasi".to_string();
-    options.vendor = String::new();
     options.linker_flavor = LinkerFlavor::Lld(LldFlavor::Wasm);
     options
         .pre_link_args