Add perma-unstable --print=backend-has-zstd for use by compiletest

compiler/rustc_codegen_llvm/src/lib.rs

@@ -257,6 +257,10 @@ impl CodegenBackend for LlvmCodegenBackend {
                 }
                 writeln!(out).unwrap();
             }
+            PrintKind::BackendHasZstd => {
+                let has_zstd = llvm::LLVMRustLLVMHasZstdCompression();
+                writeln!(out, "{has_zstd}").unwrap();
+            }
             PrintKind::CodeModels => {
                 writeln!(out, "Available code models:").unwrap();
                 for name in &["tiny", "small", "kernel", "medium", "large"] {

compiler/rustc_driver_impl/src/lib.rs

@@ -799,6 +799,7 @@ fn print_crate_info(
                 println_info!("{}", calling_conventions.join("\n"));
             }
             RelocationModels
+            | BackendHasZstd
             | CodeModels
             | TlsModels
             | TargetCPUs

compiler/rustc_session/src/config/print_request.rs

@@ -22,6 +22,7 @@ pub struct PrintRequest {
 pub enum PrintKind {
     // tidy-alphabetical-start
     AllTargetSpecsJson,
+    BackendHasZstd,
     CallingConventions,
     Cfg,
     CheckCfg,
@@ -59,6 +60,7 @@ impl PrintKind {
         match self {
             // tidy-alphabetical-start
             AllTargetSpecsJson => "all-target-specs-json",
+            BackendHasZstd => "backend-has-zstd",
             CallingConventions => "calling-conventions",
             Cfg => "cfg",
             CheckCfg => "check-cfg",
@@ -111,6 +113,7 @@ impl PrintKind {
 
             // Unstable values:
             AllTargetSpecsJson => false,
+            BackendHasZstd => false, // (perma-unstable, for use by compiletest)
             CheckCfg => false,
             CrateRootLintLevels => false,
             SupportedCrateTypes => false,

src/tools/compiletest/src/common.rs

@@ -1096,7 +1096,11 @@ fn supported_crate_types(config: &Config) -> HashSet<String> {
     crate_types
 }
 
-fn query_rustc_output(config: &Config, args: &[&str], envs: HashMap<String, String>) -> String {
+pub(crate) fn query_rustc_output(
+    config: &Config,
+    args: &[&str],
+    envs: HashMap<String, String>,
+) -> String {
     let query_rustc_path = config.query_rustc_path.as_deref().unwrap_or(&config.rustc_path);
 
     let mut command = Command::new(query_rustc_path);

src/tools/compiletest/src/directives.rs

@@ -885,107 +885,6 @@ pub fn extract_llvm_version_from_binary(binary_path: &str) -> Option<Version> {
     None
 }
 
-/// For tests using the `needs-llvm-zstd` directive:
-/// - for local LLVM builds, try to find the static zstd library in the llvm-config system libs.
-/// - for `download-ci-llvm`, see if `lld` was built with zstd support.
-pub fn llvm_has_libzstd(config: &Config) -> bool {
-    // Strategy 1: works for local builds but not with `download-ci-llvm`.
-    //
-    // We check whether `llvm-config` returns the zstd library. Bootstrap's `llvm.libzstd` will only
-    // ask to statically link it when building LLVM, so we only check if the list of system libs
-    // contains a path to that static lib, and that it exists.
-    //
-    // See compiler/rustc_llvm/build.rs for more details and similar expectations.
-    fn is_zstd_in_config(llvm_bin_dir: &Utf8Path) -> Option<()> {
-        let llvm_config_path = llvm_bin_dir.join("llvm-config");
-        let output = Command::new(llvm_config_path).arg("--system-libs").output().ok()?;
-        assert!(output.status.success(), "running llvm-config --system-libs failed");
-
-        let libs = String::from_utf8(output.stdout).ok()?;
-        for lib in libs.split_whitespace() {
-            if lib.ends_with("libzstd.a") && Utf8Path::new(lib).exists() {
-                return Some(());
-            }
-        }
-
-        None
-    }
-
-    // Strategy 2: `download-ci-llvm`'s `llvm-config --system-libs` will not return any libs to
-    // use.
-    //
-    // The CI artifacts also don't contain the bootstrap config used to build them: otherwise we
-    // could have looked at the `llvm.libzstd` config.
-    //
-    // We infer whether `LLVM_ENABLE_ZSTD` was used to build LLVM as a byproduct of testing whether
-    // `lld` supports it. If not, an error will be emitted: "LLVM was not built with
-    // LLVM_ENABLE_ZSTD or did not find zstd at build time".
-    #[cfg(unix)]
-    fn is_lld_built_with_zstd(llvm_bin_dir: &Utf8Path) -> Option<()> {
-        let lld_path = llvm_bin_dir.join("lld");
-        if lld_path.exists() {
-            // We can't call `lld` as-is, it expects to be invoked by a compiler driver using a
-            // different name. Prepare a temporary symlink to do that.
-            let lld_symlink_path = llvm_bin_dir.join("ld.lld");
-            if !lld_symlink_path.exists() {
-                std::os::unix::fs::symlink(lld_path, &lld_symlink_path).ok()?;
-            }
-
-            // Run `lld` with a zstd flag. We expect this command to always error here, we don't
-            // want to link actual files and don't pass any.
-            let output = Command::new(&lld_symlink_path)
-                .arg("--compress-debug-sections=zstd")
-                .output()
-                .ok()?;
-            assert!(!output.status.success());
-
-            // Look for a specific error caused by LLVM not being built with zstd support. We could
-            // also look for the "no input files" message, indicating the zstd flag was accepted.
-            let stderr = String::from_utf8(output.stderr).ok()?;
-            let zstd_available = !stderr.contains("LLVM was not built with LLVM_ENABLE_ZSTD");
-
-            // We don't particularly need to clean the link up (so the previous commands could fail
-            // in theory but won't in practice), but we can try.
-            std::fs::remove_file(lld_symlink_path).ok()?;
-
-            if zstd_available {
-                return Some(());
-            }
-        }
-
-        None
-    }
-
-    #[cfg(not(unix))]
-    fn is_lld_built_with_zstd(_llvm_bin_dir: &Utf8Path) -> Option<()> {
-        None
-    }
-
-    if let Some(llvm_bin_dir) = &config.llvm_bin_dir {
-        // Strategy 1: for local LLVM builds.
-        if is_zstd_in_config(llvm_bin_dir).is_some() {
-            return true;
-        }
-
-        // Strategy 2: for LLVM artifacts built on CI via `download-ci-llvm`.
-        //
-        // It doesn't work for cases where the artifacts don't contain the linker, but it's
-        // best-effort: CI has `llvm.libzstd` and `lld` enabled on the x64 linux artifacts, so it
-        // will at least work there.
-        //
-        // If this can be improved and expanded to less common cases in the future, it should.
-        if config.target == "x86_64-unknown-linux-gnu"
-            && config.host == config.target
-            && is_lld_built_with_zstd(llvm_bin_dir).is_some()
-        {
-            return true;
-        }
-    }
-
-    // Otherwise, all hope is lost.
-    false
-}
-
 /// Takes a directive of the form `"<version1> [- <version2>]"`, returns the numeric representation
 /// of `<version1>` and `<version2>` as tuple: `(<version1>, <version2>)`.
 ///

src/tools/compiletest/src/directives/needs.rs

@@ -1,5 +1,7 @@
-use crate::common::{Config, KNOWN_CRATE_TYPES, KNOWN_TARGET_HAS_ATOMIC_WIDTHS, Sanitizer};
-use crate::directives::{DirectiveLine, IgnoreDecision, llvm_has_libzstd};
+use crate::common::{
+    Config, KNOWN_CRATE_TYPES, KNOWN_TARGET_HAS_ATOMIC_WIDTHS, Sanitizer, query_rustc_output,
+};
+use crate::directives::{DirectiveLine, IgnoreDecision};
 
 pub(super) fn handle_needs(
     cache: &CachedNeedsConditions,
@@ -377,7 +379,7 @@ impl CachedNeedsConditions {
                 .join(if config.host.contains("windows") { "rust-lld.exe" } else { "rust-lld" })
                 .exists(),
 
-            llvm_zstd: llvm_has_libzstd(&config),
+            llvm_zstd: llvm_has_zstd(&config),
             dlltool: find_dlltool(&config),
             symlinks: has_symlinks(),
         }
@@ -428,3 +430,18 @@ fn has_symlinks() -> bool {
 fn has_symlinks() -> bool {
     true
 }
+
+fn llvm_has_zstd(config: &Config) -> bool {
+    // The compiler already knows whether LLVM was built with zstd or not,
+    // so compiletest can just ask the compiler.
+    let output = query_rustc_output(
+        config,
+        &["-Zunstable-options", "--print=backend-has-zstd"],
+        Default::default(),
+    );
+    match output.trim() {
+        "true" => true,
+        "false" => false,
+        _ => panic!("unexpected output from `--print=backend-has-zstd`: {output:?}"),
+    }
+}

tests/run-make/print-request-help-stable-unstable/help-diff.diff

@@ -2,6 +2,6 @@
  error: unknown print request: `xxx`
    |
 -  = help: valid print requests are: `calling-conventions`, `cfg`, `code-models`, `crate-name`, `deployment-target`, `file-names`, `host-tuple`, `link-args`, `native-static-libs`, `relocation-models`, `split-debuginfo`, `stack-protector-strategies`, `sysroot`, `target-cpus`, `target-features`, `target-libdir`, `target-list`, `tls-models`
-+  = help: valid print requests are: `all-target-specs-json`, `calling-conventions`, `cfg`, `check-cfg`, `code-models`, `crate-name`, `crate-root-lint-levels`, `deployment-target`, `file-names`, `host-tuple`, `link-args`, `native-static-libs`, `relocation-models`, `split-debuginfo`, `stack-protector-strategies`, `supported-crate-types`, `sysroot`, `target-cpus`, `target-features`, `target-libdir`, `target-list`, `target-spec-json`, `target-spec-json-schema`, `tls-models`
++  = help: valid print requests are: `all-target-specs-json`, `backend-has-zstd`, `calling-conventions`, `cfg`, `check-cfg`, `code-models`, `crate-name`, `crate-root-lint-levels`, `deployment-target`, `file-names`, `host-tuple`, `link-args`, `native-static-libs`, `relocation-models`, `split-debuginfo`, `stack-protector-strategies`, `supported-crate-types`, `sysroot`, `target-cpus`, `target-features`, `target-libdir`, `target-list`, `target-spec-json`, `target-spec-json-schema`, `tls-models`
    = help: for more information, see the rustc book: https://doc.rust-lang.org/rustc/command-line-arguments.html#--print-print-compiler-information
 

tests/run-make/print-request-help-stable-unstable/unstable-invalid-print-request-help.err

@@ -1,5 +1,5 @@
 error: unknown print request: `xxx`
   |
-  = help: valid print requests are: `all-target-specs-json`, `calling-conventions`, `cfg`, `check-cfg`, `code-models`, `crate-name`, `crate-root-lint-levels`, `deployment-target`, `file-names`, `host-tuple`, `link-args`, `native-static-libs`, `relocation-models`, `split-debuginfo`, `stack-protector-strategies`, `supported-crate-types`, `sysroot`, `target-cpus`, `target-features`, `target-libdir`, `target-list`, `target-spec-json`, `target-spec-json-schema`, `tls-models`
+  = help: valid print requests are: `all-target-specs-json`, `backend-has-zstd`, `calling-conventions`, `cfg`, `check-cfg`, `code-models`, `crate-name`, `crate-root-lint-levels`, `deployment-target`, `file-names`, `host-tuple`, `link-args`, `native-static-libs`, `relocation-models`, `split-debuginfo`, `stack-protector-strategies`, `supported-crate-types`, `sysroot`, `target-cpus`, `target-features`, `target-libdir`, `target-list`, `target-spec-json`, `target-spec-json-schema`, `tls-models`
   = help: for more information, see the rustc book: https://doc.rust-lang.org/rustc/command-line-arguments.html#--print-print-compiler-information
 

tests/run-make/rustc-help/help-v.stdout

@@ -43,7 +43,7 @@ Options:
         --print <INFO>[=<FILE>]
                         Compiler information to print on stdout (or to a file)
                         INFO may be one of
-                        <all-target-specs-json|calling-conventions|cfg|check-cfg|code-models|crate-name|crate-root-lint-levels|deployment-target|file-names|host-tuple|link-args|native-static-libs|relocation-models|split-debuginfo|stack-protector-strategies|supported-crate-types|sysroot|target-cpus|target-features|target-libdir|target-list|target-spec-json|target-spec-json-schema|tls-models>.
+                        <all-target-specs-json|backend-has-zstd|calling-conventions|cfg|check-cfg|code-models|crate-name|crate-root-lint-levels|deployment-target|file-names|host-tuple|link-args|native-static-libs|relocation-models|split-debuginfo|stack-protector-strategies|supported-crate-types|sysroot|target-cpus|target-features|target-libdir|target-list|target-spec-json|target-spec-json-schema|tls-models>.
     -g                  Equivalent to -C debuginfo=2
     -O                  Equivalent to -C opt-level=3
     -o <FILENAME>       Write output to FILENAME

tests/run-make/rustc-help/help.stdout

@@ -43,7 +43,7 @@ Options:
         --print <INFO>[=<FILE>]
                         Compiler information to print on stdout (or to a file)
                         INFO may be one of
-                        <all-target-specs-json|calling-conventions|cfg|check-cfg|code-models|crate-name|crate-root-lint-levels|deployment-target|file-names|host-tuple|link-args|native-static-libs|relocation-models|split-debuginfo|stack-protector-strategies|supported-crate-types|sysroot|target-cpus|target-features|target-libdir|target-list|target-spec-json|target-spec-json-schema|tls-models>.
+                        <all-target-specs-json|backend-has-zstd|calling-conventions|cfg|check-cfg|code-models|crate-name|crate-root-lint-levels|deployment-target|file-names|host-tuple|link-args|native-static-libs|relocation-models|split-debuginfo|stack-protector-strategies|supported-crate-types|sysroot|target-cpus|target-features|target-libdir|target-list|target-spec-json|target-spec-json-schema|tls-models>.
     -g                  Equivalent to -C debuginfo=2
     -O                  Equivalent to -C opt-level=3
     -o <FILENAME>       Write output to FILENAME

tests/ui/invalid-compile-flags/print-without-arg.stderr

@@ -3,5 +3,5 @@ error: Argument to option 'print' missing
            --print <INFO>[=<FILE>]
                                Compiler information to print on stdout (or to a file)
                                INFO may be one of
-                               <all-target-specs-json|calling-conventions|cfg|check-cfg|code-models|crate-name|crate-root-lint-levels|deployment-target|file-names|host-tuple|link-args|native-static-libs|relocation-models|split-debuginfo|stack-protector-strategies|supported-crate-types|sysroot|target-cpus|target-features|target-libdir|target-list|target-spec-json|target-spec-json-schema|tls-models>.
+                               <all-target-specs-json|backend-has-zstd|calling-conventions|cfg|check-cfg|code-models|crate-name|crate-root-lint-levels|deployment-target|file-names|host-tuple|link-args|native-static-libs|relocation-models|split-debuginfo|stack-protector-strategies|supported-crate-types|sysroot|target-cpus|target-features|target-libdir|target-list|target-spec-json|target-spec-json-schema|tls-models>.
 

tests/ui/invalid-compile-flags/print.stderr

@@ -1,5 +1,5 @@
 error: unknown print request: `yyyy`
   |
-  = help: valid print requests are: `all-target-specs-json`, `calling-conventions`, `cfg`, `check-cfg`, `code-models`, `crate-name`, `crate-root-lint-levels`, `deployment-target`, `file-names`, `host-tuple`, `link-args`, `native-static-libs`, `relocation-models`, `split-debuginfo`, `stack-protector-strategies`, `supported-crate-types`, `sysroot`, `target-cpus`, `target-features`, `target-libdir`, `target-list`, `target-spec-json`, `target-spec-json-schema`, `tls-models`
+  = help: valid print requests are: `all-target-specs-json`, `backend-has-zstd`, `calling-conventions`, `cfg`, `check-cfg`, `code-models`, `crate-name`, `crate-root-lint-levels`, `deployment-target`, `file-names`, `host-tuple`, `link-args`, `native-static-libs`, `relocation-models`, `split-debuginfo`, `stack-protector-strategies`, `supported-crate-types`, `sysroot`, `target-cpus`, `target-features`, `target-libdir`, `target-list`, `target-spec-json`, `target-spec-json-schema`, `tls-models`
   = help: for more information, see the rustc book: https://doc.rust-lang.org/rustc/command-line-arguments.html#--print-print-compiler-information
 

tests/ui/print-request/backend-has-zstd-unstable.rs

@@ -0,0 +1,8 @@
+//! Check that `--print=backend-has-zstd` is unstable.
+//!
+//! That print value is intended for use by compiletest, and should probably
+//! never be stabilized in this form.
+
+//@ compile-flags: --print=backend-has-zstd
+
+//~? ERROR: the `-Z unstable-options` flag must also be passed

tests/ui/print-request/backend-has-zstd-unstable.stderr

@@ -0,0 +1,2 @@
+error: the `-Z unstable-options` flag must also be passed to enable the `backend-has-zstd` print option
+

tests/ui/print-request/print-lints-help.stderr

@@ -1,6 +1,6 @@
 error: unknown print request: `lints`
   |
-  = help: valid print requests are: `all-target-specs-json`, `calling-conventions`, `cfg`, `check-cfg`, `code-models`, `crate-name`, `crate-root-lint-levels`, `deployment-target`, `file-names`, `host-tuple`, `link-args`, `native-static-libs`, `relocation-models`, `split-debuginfo`, `stack-protector-strategies`, `supported-crate-types`, `sysroot`, `target-cpus`, `target-features`, `target-libdir`, `target-list`, `target-spec-json`, `target-spec-json-schema`, `tls-models`
+  = help: valid print requests are: `all-target-specs-json`, `backend-has-zstd`, `calling-conventions`, `cfg`, `check-cfg`, `code-models`, `crate-name`, `crate-root-lint-levels`, `deployment-target`, `file-names`, `host-tuple`, `link-args`, `native-static-libs`, `relocation-models`, `split-debuginfo`, `stack-protector-strategies`, `supported-crate-types`, `sysroot`, `target-cpus`, `target-features`, `target-libdir`, `target-list`, `target-spec-json`, `target-spec-json-schema`, `tls-models`
   = help: use `-Whelp` to print a list of lints
   = help: for more information, see the rustc book: https://doc.rust-lang.org/rustc/command-line-arguments.html#--print-print-compiler-information