[lld] [ELF] Add context-aware diagnostic functions (PR #112319)

[Peter Smith via llvm-commits]

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@@ -679,6 +681,25 @@ static inline void internalLinkerError(StringRef loc, const Twine &msg) {
               llvm::getBugReportMsg());
 }
 
+struct ELFSyncStream : SyncStream {
+  Ctx &ctx;
+  ELFSyncStream(Ctx &ctx, DiagLevel level)
+      : SyncStream(*ctx.e, level), ctx(ctx) {}
+};
+
+template <typename T>
+std::enable_if_t<!std::is_pointer_v<std::remove_reference_t<T>>,
+                 const ELFSyncStream &>
+operator<<(const ELFSyncStream &s, T &&v) {
+  s.os << std::forward<T>(v);
+  return s;
+}
+
+ELFSyncStream Log(Ctx &ctx);
+ELFSyncStream Warn(Ctx &ctx);
+ELFSyncStream Err(Ctx &ctx);
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smithp35 wrote:

If `Err` is the default, then perhaps `ErrAlways` for the non downgradeable variety. If it isn't as common it could have a longer name.

Alternatives: `ForceErr`, `PermErr`, `AlwaysErr`. 

https://github.com/llvm/llvm-project/pull/112319