fix(driver): cache the embedded standard library per user

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

3 files changed, 78 insertions, 21 deletions

diff --git a/tools/driver/NativeCompiler.cc b/tools/driver/NativeCompiler.cc
index dc1f068..fa3d2a1 100644
--- a/tools/driver/NativeCompiler.cc
+++ b/tools/driver/NativeCompiler.cc
@@ -337,8 +337,7 @@ bool compileNative(const cps::CodeGen &CG, llvm::StringRef OutputPath, const cha
 #endif
     LinkArgs.append(Job.getArguments().begin(), Job.getArguments().end());
     auto Result = lld::lldMain(LinkArgs, llvm::outs(), llvm::errs(), Linkers);
-    if (!Result.canRunAgain) std::exit(1);
-    if (Result.retCode != 0) return fail("native linking failed");
+    if (!Result.canRunAgain || Result.retCode != 0) return fail("native linking failed");
     if (auto EC = llvm::sys::fs::setPermissions(StagedPath,
             llvm::sys::fs::all_read | llvm::sys::fs::owner_write | llvm::sys::fs::all_exe))
         return fail("cannot set executable permissions: " + EC.message());
diff --git a/tools/driver/StandardLibrary.cc b/tools/driver/StandardLibrary.cc
index 7680054..a2b3168 100644
--- a/tools/driver/StandardLibrary.cc
+++ b/tools/driver/StandardLibrary.cc
@@ -1,8 +1,12 @@
 #include "StandardLibrary.h"
 #include "cps/Diagnostics.h"
+#include "llvm/ADT/StringExtras.h"
+#include "llvm/Support/Error.h"
 #include "llvm/Support/FileSystem.h"
+#include "llvm/Support/MemoryBuffer.h"
 #include "llvm/Support/Path.h"
 #include "llvm/Support/raw_ostream.h"
+#include "llvm/Support/xxhash.h"
 
 namespace {
 struct LibraryFile {
@@ -14,31 +18,83 @@ struct LibraryFile {
 }
 
 StandardLibrary::~StandardLibrary() {
-    if (!Directory.empty()) llvm::sys::fs::remove_directories(Directory);
+    if (!Directory.empty() && Temporary) llvm::sys::fs::remove_directories(Directory);
+}
+
+namespace {
+std::string contentKey() {
+    std::string Bytes;
+    for (const auto &File : LibraryFiles) {
+        Bytes.append(File.Name);
+        Bytes.push_back('\0');
+        Bytes.append(File.Data, File.Size);
+    }
+    return llvm::utohexstr(llvm::xxh3_64bits(llvm::ArrayRef<uint8_t>(
+        reinterpret_cast<const uint8_t *>(Bytes.data()), Bytes.size())), true);
+}
+
+bool sameContents(const llvm::Twine &Path, const LibraryFile &File) {
+    auto Existing = llvm::MemoryBuffer::getFile(Path);
+    return Existing && (*Existing)->getBuffer() == llvm::StringRef(File.Data, File.Size);
+}
+
+// Atomically publishes the bytes at Path; concurrent runs never see partial files.
+std::error_code publish(llvm::StringRef Directory, llvm::StringRef Path, const LibraryFile &File) {
+    llvm::SmallString<256> Pattern(Directory);
+    llvm::sys::path::append(Pattern, "tmp-%%%%%%%%");
+    auto Temp = llvm::sys::fs::TempFile::create(Pattern);
+    if (!Temp) return llvm::errorToErrorCode(Temp.takeError());
+    llvm::raw_fd_ostream Output(Temp->FD, false);
+    Output.write(File.Data, File.Size);
+    Output.flush();
+    if (Output.has_error()) {
+        auto EC = Output.error();
+        Output.clear_error();
+        llvm::consumeError(Temp->discard());
+        return EC;
+    }
+    if (auto Error = Temp->keep(Path)) return llvm::errorToErrorCode(std::move(Error));
+    return {};
+}
 }
 
 bool StandardLibrary::load(std::vector<std::string> &Inputs) {
-    auto Error = llvm::sys::fs::createUniqueDirectory("cpsc-std", Directory);
-    if (Error) {
-        llvm::errs() << cps::diagnosticPrefix(cps::Severity::Fatal)
-                     << "cannot extract standard library: " << Error.message() << "\n";
-        return false;
+    // The extracted files are cached per user and keyed by content, so killed runs leave nothing behind.
+    llvm::SmallString<256> Cache;
+    if (llvm::sys::path::cache_directory(Cache)) {
+        llvm::sys::path::append(Cache, "cpsc", "std-" + contentKey());
+        if (!llvm::sys::fs::create_directories(Cache)) Directory = Cache;
+    }
+    if (Directory.empty()) {
+        Temporary = true;
+        if (auto Error = llvm::sys::fs::createUniqueDirectory("cpsc-std", Directory)) {
+            llvm::errs() << cps::diagnosticPrefix(cps::Severity::Fatal)
+                         << "cannot extract standard library: " << Error.message() << "\n";
+            return false;
+        }
     }
     for (const auto &File : LibraryFiles) {
         llvm::SmallString<256> Path(Directory);
         llvm::sys::path::append(Path, File.Name);
-        llvm::raw_fd_ostream Output(Path, Error);
-        if (!Error) {
-            Output.write(File.Data, File.Size);
-            Output.close();
-            Error = Output.error();
-        }
-        if (Error) {
-            llvm::errs() << cps::diagnosticPrefix(cps::Severity::Fatal)
-                         << "cannot extract standard library file '" << File.Name
-                         << "': " << Error.message() << "\n";
-            Output.clear_error();
-            return false;
+        if (!(!Temporary && sameContents(Path, File))) {
+            std::error_code Error;
+            if (Temporary) {
+                llvm::raw_fd_ostream Output(Path, Error);
+                if (!Error) {
+                    Output.write(File.Data, File.Size);
+                    Output.close();
+                    Error = Output.error();
+                    Output.clear_error();
+                }
+            } else {
+                Error = publish(Directory, Path, File);
+            }
+            if (Error) {
+                llvm::errs() << cps::diagnosticPrefix(cps::Severity::Fatal)
+                             << "cannot extract standard library file '" << File.Name
+                             << "': " << Error.message() << "\n";
+                return false;
+            }
         }
         if (llvm::sys::path::extension(Path) == ".cps") Inputs.emplace_back(Path);
     }
diff --git a/tools/driver/StandardLibrary.h b/tools/driver/StandardLibrary.h
index 5aa4f8c..0e641d0 100644
--- a/tools/driver/StandardLibrary.h
+++ b/tools/driver/StandardLibrary.h
@@ -3,9 +3,11 @@
 #include <string>
 #include <vector>
 
-// Extracted files live through native linking and runner execution.
+// Extracted files live through native linking and runner execution. They are cached per user
+// (never deleted); only the fallback temporary directory is removed on destruction.
 class StandardLibrary {
     llvm::SmallString<256> Directory;
+    bool Temporary = false;
 public:
     ~StandardLibrary();
     bool load(std::vector<std::string> &Inputs);