treewide: Make exceptions cloneable

This is needed to make it possible to store exceptions in failed values
with each new rethrow getting a fresh copy of the exception object.

src/libexpr/eval-cache.cc

@@ -11,7 +11,7 @@
 namespace nix::eval_cache {
 
 CachedEvalError::CachedEvalError(ref<AttrCursor> cursor, Symbol attr)
-    : EvalError(cursor->root->state, "cached failure of attribute '%s'", cursor->getAttrPathStr(attr))
+    : CloneableError(cursor->root->state, "cached failure of attribute '%s'", cursor->getAttrPathStr(attr))
     , cursor(cursor)
     , attr(attr)
 {

src/libexpr/include/nix/expr/eval-cache.hh

@@ -14,7 +14,7 @@ namespace nix::eval_cache {
 struct AttrDb;
 class AttrCursor;
 
-struct CachedEvalError : EvalError
+struct CachedEvalError : CloneableError<CachedEvalError, EvalError>
 {
     const ref<AttrCursor> cursor;
     const Symbol attr;

src/libexpr/include/nix/expr/eval-error.hh

@@ -18,7 +18,7 @@ class EvalErrorBuilder;
  *
  * Most subclasses should inherit from `EvalError` instead of this class.
  */
-class EvalBaseError : public Error
+class EvalBaseError : public CloneableError<EvalBaseError, Error>
 {
     template<class T>
     friend class EvalErrorBuilder;
@@ -26,14 +26,14 @@ public:
     EvalState & state;
 
     EvalBaseError(EvalState & state, ErrorInfo && errorInfo)
-        : Error(errorInfo)
+        : CloneableError(errorInfo)
         , state(state)
     {
     }
 
     template<typename... Args>
     explicit EvalBaseError(EvalState & state, const std::string & formatString, const Args &... formatArgs)
-        : Error(formatString, formatArgs...)
+        : CloneableError(formatString, formatArgs...)
         , state(state)
     {
     }
@@ -60,23 +60,23 @@ MakeError(InfiniteRecursionError, EvalError);
  * Inherits from EvalBaseError (not EvalError) because resource exhaustion
  * should not be cached.
  */
-struct StackOverflowError : public EvalBaseError
+struct StackOverflowError : public CloneableError<StackOverflowError, EvalBaseError>
 {
     StackOverflowError(EvalState & state)
-        : EvalBaseError(state, "stack overflow; max-call-depth exceeded")
+        : CloneableError(state, "stack overflow; max-call-depth exceeded")
     {
     }
 };
 
 MakeError(IFDError, EvalBaseError);
 
-struct InvalidPathError : public EvalError
+struct InvalidPathError : public CloneableError<InvalidPathError, EvalError>
 {
 public:
     Path path;
 
     InvalidPathError(EvalState & state, const Path & path)
-        : EvalError(state, "path '%s' is not valid", path)
+        : CloneableError(state, "path '%s' is not valid", path)
     {
     }
 };

src/libexpr/include/nix/expr/value/context.hh

@@ -9,14 +9,14 @@
 
 namespace nix {
 
-class BadNixStringContextElem : public Error
+class BadNixStringContextElem final : public CloneableError<BadNixStringContextElem, Error>
 {
 public:
     std::string_view raw;
 
     template<typename... Args>
     BadNixStringContextElem(std::string_view raw_, const Args &... args)
-        : Error("")
+        : CloneableError("")
     {
         raw = raw_;
         auto hf = HintFmt(args...);

src/libexpr/primops.cc

@@ -1312,11 +1312,12 @@ static void prim_warn(EvalState & state, const PosIdx pos, Value ** args, Value
         state.forceString(*args[0], pos, "while evaluating the first argument; the message passed to builtins.warn");
 
     {
-        BaseError msg(std::string{msgStr});
-        msg.atPos(state.positions[pos]);
-        auto info = msg.info();
-        info.level = lvlWarn;
-        info.isFromExpr = true;
+        ErrorInfo info{
+            .level = lvlWarn,
+            .msg = HintFmt(std::string(msgStr)),
+            .pos = state.positions[pos],
+            .isFromExpr = true,
+        };
         logWarning(info);
     }
 

src/libfetchers/git-utils.cc

@@ -74,11 +74,11 @@ namespace nix {
 
 struct GitSourceAccessor;
 
-struct GitError : public Error
+struct GitError final : public CloneableError<GitError, Error>
 {
     template<typename... Ts>
     GitError(const git_error & error, Ts &&... args)
-        : Error("")
+        : CloneableError("")
     {
         auto hf = HintFmt(std::forward<Ts>(args)...);
         err.msg = HintFmt("%1%: %2% (libgit2 error code = %3%)", Uncolored(hf.str()), error.message, error.klass);

src/libstore/aws-creds.cc

@@ -28,7 +28,7 @@
 namespace nix {
 
 AwsAuthError::AwsAuthError(int errorCode)
-    : Error("AWS authentication error: '%s' (%d)", aws_error_str(errorCode), errorCode)
+    : CloneableError("AWS authentication error: '%s' (%d)", aws_error_str(errorCode), errorCode)
     , errorCode(errorCode)
 {
 }

src/libstore/build/goal.cc

@@ -1,11 +1,11 @@
 #include "nix/store/build/goal.hh"
 #include "nix/store/build/worker.hh"
-#include "nix/store/globals.hh"
+#include "nix/store/worker-settings.hh"
 
 namespace nix {
 
 TimedOut::TimedOut(time_t maxDuration)
-    : BuildError(BuildResult::Failure::TimedOut, "timed out after %1% seconds", maxDuration)
+    : CloneableError(BuildResult::Failure::TimedOut, "timed out after %1% seconds", maxDuration)
     , maxDuration(maxDuration)
 {
 }

src/libstore/filetransfer.cc

@@ -60,12 +60,12 @@ namespace {
 using curlSList = std::unique_ptr<::curl_slist, decltype([](::curl_slist * list) { ::curl_slist_free_all(list); })>;
 using curlMulti = std::unique_ptr<::CURLM, decltype([](::CURLM * multi) { ::curl_multi_cleanup(multi); })>;
 
-struct curlMultiError : Error
+struct curlMultiError final : CloneableError<curlMultiError, Error>
 {
     ::CURLMcode code;
 
     curlMultiError(::CURLMcode code)
-        : Error{"unexpected curl multi error: %s", ::curl_multi_strerror(code)}
+        : CloneableError{"unexpected curl multi error: %s", ::curl_multi_strerror(code)}
     {
         assert(code != CURLM_OK);
     }
@@ -1212,7 +1212,7 @@ void FileTransfer::download(
 template<typename... Args>
 FileTransferError::FileTransferError(
     FileTransfer::Error error, std::optional<std::string> response, const Args &... args)
-    : Error(args...)
+    : CloneableError(args...)
     , error(error)
     , response(response)
 {

src/libstore/include/nix/store/aws-creds.hh

@@ -34,12 +34,13 @@ struct AwsCredentials
     }
 };
 
-class AwsAuthError : public Error
+class AwsAuthError final : public CloneableError<AwsAuthError, Error>
 {
     std::optional<int> errorCode;
 
 public:
-    using Error::Error;
+    using CloneableError::CloneableError;
+
     AwsAuthError(int errorCode);
 
     std::optional<int> getErrorCode() const

src/libstore/include/nix/store/build-result.hh

@@ -58,7 +58,7 @@ enum struct BuildResultFailureStatus : uint8_t {
  * This is both an exception type (inherits from Error) and serves as
  * the failure variant in BuildResult::inner.
  */
-struct BuildError : public Error
+struct BuildError : public CloneableError<BuildError, Error>
 {
     using Status = BuildResultFailureStatus;
     using enum Status;
@@ -80,7 +80,7 @@ public:
      */
     template<typename... Args>
     BuildError(Status status, const Args &... args)
-        : Error(args...)
+        : CloneableError(args...)
         , status{status}
     {
     }
@@ -97,7 +97,7 @@ public:
      * Also used for deserialization.
      */
     BuildError(Args args)
-        : Error(std::move(args.msg))
+        : CloneableError(std::move(args.msg))
         , status{args.status}
         , isNonDeterministic{args.isNonDeterministic}
 
@@ -108,7 +108,7 @@ public:
      * Default constructor for deserialization.
      */
     BuildError()
-        : Error("")
+        : CloneableError("")
     {
     }
 

src/libstore/include/nix/store/build/derivation-builder.hh

@@ -20,14 +20,14 @@ namespace nix {
  * Denotes a build failure that stemmed from the builder exiting with a
  * failing exist status.
  */
-struct BuilderFailureError : BuildError
+struct BuilderFailureError final : CloneableError<BuilderFailureError, BuildError>
 {
     int builderStatus;
 
     std::string extraMsgAfter;
 
     BuilderFailureError(BuildResult::Failure::Status status, int builderStatus, std::string extraMsgAfter)
-        : BuildError{
+        : CloneableError{
             status,
               /* No message for now, because the caller will make for
                  us, with extra context */

src/libstore/include/nix/store/build/goal.hh

@@ -10,7 +10,7 @@
 
 namespace nix {
 
-struct TimedOut : BuildError
+struct TimedOut final : CloneableError<TimedOut, BuildError>
 {
     time_t maxDuration;
 

src/libstore/include/nix/store/builtins/buildenv.hh

@@ -22,7 +22,7 @@ struct Package
     }
 };
 
-class BuildEnvFileConflictError : public Error
+class BuildEnvFileConflictError final : public CloneableError<BuildEnvFileConflictError, Error>
 {
 public:
     const Path fileA;
@@ -30,7 +30,7 @@ public:
     int priority;
 
     BuildEnvFileConflictError(const Path fileA, const Path fileB, int priority)
-        : Error(
+        : CloneableError(
               "Unable to build profile. There is a conflict for the following files:\n"
               "\n"
               "  %1%\n"

src/libstore/include/nix/store/filetransfer.hh

@@ -403,7 +403,7 @@ ref<FileTransfer> getFileTransfer();
  */
 ref<FileTransfer> makeFileTransfer(const FileTransferSettings & settings = fileTransferSettings);
 
-class FileTransferError : public Error
+class FileTransferError final : public CloneableError<FileTransferError, Error>
 {
 public:
     FileTransfer::Error error;

src/libstore/include/nix/store/realisation.hh

@@ -146,7 +146,7 @@ struct RealisedPath
     auto operator<=>(const RealisedPath &) const = default;
 };
 
-class MissingRealisation : public Error
+class MissingRealisation final : public CloneableError<MissingRealisation, Error>
 {
 public:
     MissingRealisation(DrvOutput & outputId)
@@ -155,7 +155,7 @@ public:
     }
 
     MissingRealisation(std::string_view drv, OutputName outputName)
-        : Error(
+        : CloneableError(
               "cannot operate on output '%s' of the "
               "unbuilt derivation '%s'",
               outputName,

src/libstore/include/nix/store/sqlite.hh

@@ -166,7 +166,7 @@ struct SQLiteTxn
     ~SQLiteTxn();
 };
 
-struct SQLiteError : Error
+struct SQLiteError : CloneableError<SQLiteError, Error>
 {
     std::string path;
     std::string errMsg;

src/libstore/sqlite.cc

@@ -17,7 +17,7 @@ namespace nix {
 
 SQLiteError::SQLiteError(
     const char * path, const char * errMsg, int errNo, int extendedErrNo, int offset, HintFmt && hf)
-    : Error("")
+    : CloneableError("")
     , path(path)
     , errMsg(errMsg)
     , errNo(errNo)

src/libstore/ssh.cc

@@ -18,11 +18,11 @@ static std::string parsePublicHostKey(std::string_view host, std::string_view ss
     }
 }
 
-class InvalidSSHAuthority : public Error
+class InvalidSSHAuthority final : public CloneableError<InvalidSSHAuthority, Error>
 {
 public:
     InvalidSSHAuthority(const ParsedURL::Authority & authority, std::string_view reason)
-        : Error("invalid SSH authority: '%s': %s", authority.to_string(), reason)
+        : CloneableError("invalid SSH authority: '%s': %s", authority.to_string(), reason)
     {
     }
 };

src/libstore/unix/build/derivation-builder.cc

@@ -55,10 +55,10 @@
 
 namespace nix {
 
-struct NotDeterministic : BuildError
+struct NotDeterministic final : CloneableError<NotDeterministic, BuildError>
 {
     NotDeterministic(auto &&... args)
-        : BuildError(BuildResult::Failure::NotDeterministic, args...)
+        : CloneableError(BuildResult::Failure::NotDeterministic, args...)
     {
         isNonDeterministic = true;
     }

src/libutil/experimental-features.cc

@@ -378,7 +378,7 @@ std::set<ExperimentalFeature> parseFeatures(const StringSet & rawFeatures)
 }
 
 MissingExperimentalFeature::MissingExperimentalFeature(ExperimentalFeature feature, std::string reason)
-    : Error(
+    : CloneableError(
           "experimental Nix feature '%1%' is disabled%2%; add '--extra-experimental-features %1%' to enable it",
           showExperimentalFeature(feature),
           Uncolored(optionalBracket(" (", reason, ")")))

src/libutil/include/nix/util/error.hh

@@ -226,13 +226,31 @@ public:
     {
         return err;
     };
+
+    [[noreturn]] virtual void throwClone() const = 0;
 };
 
-#define MakeError(newClass, superClass) \
-    class newClass : public superClass  \
-    {                                   \
-    public:                             \
-        using superClass::superClass;   \
+template<typename Derived, typename Base>
+class CloneableError : public Base
+{
+public:
+    using Base::Base;
+
+    /**
+     * Rethrow a copy of this exception. Useful when the exception can get
+     * modified when appending traces.
+     */
+    [[noreturn]] void throwClone() const override
+    {
+        throw Derived(static_cast<const Derived &>(*this));
+    }
+};
+
+#define MakeError(newClass, superClass)                             \
+    class newClass : public CloneableError<newClass, superClass>    \
+    {                                                               \
+    public:                                                         \
+        using CloneableError<newClass, superClass>::CloneableError; \
     }
 
 MakeError(Error, BaseError);
@@ -244,21 +262,21 @@ MakeError(UnimplementedError, Error);
  * std::error_code. Use when you want to catch and check an error condition like
  * no_such_file_or_directory (ENOENT) without ifdefs.
  */
-class SystemError : public Error
+class SystemError : public CloneableError<SystemError, Error>
 {
     std::error_code errorCode;
 
 public:
     template<typename... Args>
     SystemError(std::errc posixErrNo, Args &&... args)
-        : Error(std::forward<Args>(args)...)
+        : CloneableError(std::forward<Args>(args)...)
         , errorCode(std::make_error_code(posixErrNo))
     {
     }
 
     template<typename... Args>
     SystemError(std::error_code errorCode, Args &&... args)
-        : Error(std::forward<Args>(args)...)
+        : CloneableError(std::forward<Args>(args)...)
         , errorCode(errorCode)
     {
     }
@@ -290,7 +308,7 @@ public:
  * support is too WIP to justify the code churn, but if it is finished
  * then a better identifier becomes moe worth it.
  */
-class SysError : public SystemError
+class SysError final : public CloneableError<SysError, SystemError>
 {
 public:
     int errNo;
@@ -301,7 +319,7 @@ public:
      */
     template<typename... Args>
     SysError(int errNo, const Args &... args)
-        : SystemError(static_cast<std::errc>(errNo), "")
+        : CloneableError(static_cast<std::errc>(errNo), "")
         , errNo(errNo)
     {
         auto hf = HintFmt(args...);
@@ -369,7 +387,7 @@ namespace windows {
  * Unless you need to catch a specific error number, don't catch this in
  * portable code. Catch `SystemError` instead.
  */
-class WinError : public SystemError
+class WinError : public CloneableError<WinError, SystemError>
 {
 public:
     DWORD lastError;
@@ -381,7 +399,7 @@ public:
      */
     template<typename... Args>
     WinError(DWORD lastError, const Args &... args)
-        : SystemError(std::error_code(lastError, std::system_category()), "")
+        : CloneableError(std::error_code(lastError, std::system_category()), "")
         , lastError(lastError)
     {
         auto hf = HintFmt(args...);

src/libutil/include/nix/util/experimental-features.hh

@@ -80,7 +80,7 @@ std::set<ExperimentalFeature> parseFeatures(const StringSet &);
  * An experimental feature was required for some (experimental)
  * operation, but was not enabled.
  */
-class MissingExperimentalFeature : public Error
+class MissingExperimentalFeature final : public CloneableError<MissingExperimentalFeature, Error>
 {
 public:
     /**

src/libutil/include/nix/util/processes.hh

@@ -133,14 +133,14 @@ std::pair<int, std::string> runProgram(RunOptions && options);
 
 void runProgram2(const RunOptions & options);
 
-class ExecError : public Error
+class ExecError final : public CloneableError<ExecError, Error>
 {
 public:
     int status;
 
     template<typename... Args>
     ExecError(int status, const Args &... args)
-        : Error(args...)
+        : CloneableError(args...)
         , status(status)
     {
     }

src/libutil/include/nix/util/source-accessor.hh

@@ -231,19 +231,19 @@ ref<SourceAccessor> makeEmptySourceAccessor();
  */
 MakeError(RestrictedPathError, Error);
 
-struct SymlinkNotAllowed : public Error
+struct SymlinkNotAllowed final : public CloneableError<SymlinkNotAllowed, Error>
 {
     CanonPath path;
 
     SymlinkNotAllowed(CanonPath path)
-        : Error("relative path '%s' points to a symlink, which is not allowed", path.rel())
+        : CloneableError("relative path '%s' points to a symlink, which is not allowed", path.rel())
         , path(std::move(path))
     {
     }
 
     template<typename... Args>
     SymlinkNotAllowed(CanonPath path, const std::string & fs, Args &&... args)
-        : Error(fs, std::forward<Args>(args)...)
+        : CloneableError(fs, std::forward<Args>(args)...)
         , path(std::move(path))
     {
     }