Unknown -> Unsupported compression algorithm

Both zstd and zlib are *known* compression algorithms, they just may not
be supported by the backend. We shouldn't mislead users into e.g.
thinking they made a typo.

compiler/rustc_codegen_llvm/src/back/write.rs

@@ -36,7 +36,7 @@
 use crate::common::AsCCharPtr;
 use crate::errors::{
     CopyBitcode, FromLlvmDiag, FromLlvmOptimizationDiag, LlvmError, ParseTargetMachineConfig,
-    UnknownCompression, WithLlvmError, WriteBytecode,
+    UnsupportedCompression, WithLlvmError, WriteBytecode,
 };
 use crate::llvm::diagnostic::OptimizationDiagnosticKind::*;
 use crate::llvm::{self, DiagnosticInfo};
@@ -248,7 +248,7 @@ pub(crate) fn target_machine_factory(
             if llvm::LLVMRustLLVMHasZlibCompression() {
                 llvm::CompressionKind::Zlib
             } else {
-                sess.dcx().emit_warn(UnknownCompression { algorithm: "zlib" });
+                sess.dcx().emit_warn(UnsupportedCompression { algorithm: "zlib" });
                 llvm::CompressionKind::None
             }
         }
@@ -256,7 +256,7 @@ pub(crate) fn target_machine_factory(
             if llvm::LLVMRustLLVMHasZstdCompression() {
                 llvm::CompressionKind::Zstd
             } else {
-                sess.dcx().emit_warn(UnknownCompression { algorithm: "zstd" });
+                sess.dcx().emit_warn(UnsupportedCompression { algorithm: "zstd" });
                 llvm::CompressionKind::None
             }
         }

compiler/rustc_codegen_llvm/src/errors.rs

@@ -182,9 +182,9 @@ pub(crate) struct CopyBitcode {
 
 #[derive(Diagnostic)]
 #[diag(
-    "unknown debuginfo compression algorithm {$algorithm} - will fall back to uncompressed debuginfo"
+    "unsupported debuginfo compression algorithm {$algorithm} - will fall back to uncompressed debuginfo"
 )]
-pub(crate) struct UnknownCompression {
+pub(crate) struct UnsupportedCompression {
     pub algorithm: &'static str,
 }
 

tests/run-make/compressed-debuginfo/rmake.rs

@@ -23,7 +23,7 @@ fn check_compression(compression: &str, to_find: &str) {
         } else {
             assert_contains(
                 stderr,
-                format!("unknown debuginfo compression algorithm {compression}"),
+                format!("unsupported debuginfo compression algorithm {compression}"),
             );
         }
     });