[Support] Allow customizing the cache pruning prefix

[phosek]

Summary

Enable changing the prefix used by the cache pruning implementation.

[pcc]

What is the use case?

[phosek]

In D91555#2397902, @pcc wrote:

What is the use case?

We would like to use the cache pruning in one of our downstream tools but we would like to use a custom prefix.

llvm/include/llvm/Support/CachePruning.h

78

Alternatively, we could also make this a part of CachePruningPolicy, I'm not sure if that would be preferable?

llvm/include/llvm/Support/CachePruning.h

 // various policies.
 //
 //===----------------------------------------------------------------------===//
 
 #ifndef LLVM_SUPPORT_CACHE_PRUNING_H
 #define LLVM_SUPPORT_CACHE_PRUNING_H
 
 #include "llvm/ADT/Optional.h"
+#include "llvm/ADT/Twine.h"
 #include <chrono>
 
 namespace llvm {
 
 template <typename T> class Expected;
 class StringRef;
 
 /// Policy for the pruneCache() function. A default constructed

 /// which means a pruning interval of 30 seconds, expiration time of 24 hours
 /// and maximum cache size of 50% of available disk space.
 Expected<CachePruningPolicy> parseCachePruningPolicy(StringRef PolicyStr);
 
 /// Peform pruning using the supplied policy, returns true if pruning
 /// occurred, i.e. if Policy.Interval was expired.
 ///
 /// As a safeguard against data loss if the user specifies the wrong directory
-/// as their cache directory, this function will ignore files not matching the
-/// pattern "llvmcache-*".
-bool pruneCache(StringRef Path, CachePruningPolicy Policy);
+/// as their cache directory, this function will ignore files whose name does
+/// not start with Prefix.
+bool pruneCache(StringRef Path, CachePruningPolicy Policy,
+                Twine Prefix = "llvmcache");
 
 } // namespace llvm
 
 #endif

llvm/lib/Support/CachePruning.cpp

if (Key == "prune_interval") {
                                      inconvertibleErrorCode());
     }
   }
 
   return Policy;
 }
 
 /// Prune the cache of files that haven't been accessed in a long time.
-bool llvm::pruneCache(StringRef Path, CachePruningPolicy Policy) {
+bool llvm::pruneCache(StringRef Path, CachePruningPolicy Policy,
+                      Twine Prefix) {
   using namespace std::chrono;
 
   if (Path.empty())
     return false;
 
   bool isPathDir;
   if (sys::fs::is_directory(Path, isPathDir))
     return false;
if (Policy.Expiration == seconds(0) &&
       Policy.MaxSizeBytes == 0 && Policy.MaxSizeFiles == 0) {
     LLVM_DEBUG(dbgs() << "No pruning settings set, exit early\n");
     // Nothing will be pruned, early exit
     return false;
   }
 
   // Try to stat() the timestamp file.
   SmallString<128> TimestampFile(Path);
-  sys::path::append(TimestampFile, "llvmcache.timestamp");
+  sys::path::append(TimestampFile, Prefix + ".timestamp");
   sys::fs::file_status FileStatus;
   const auto CurrentTime = system_clock::now();
   if (auto EC = sys::fs::status(TimestampFile, FileStatus)) {
     if (EC == errc::no_such_file_or_directory) {
       // If the timestamp file wasn't there, create one now.
       writeTimestampFile(TimestampFile);
     } else {
       // Unknown error?
bool llvm::pruneCache(StringRef Path, CachePruningPolicy Policy,
 
   // Walk the entire directory cache, looking for unused files.
   std::error_code EC;
   SmallString<128> CachePathNative;
   sys::path::native(Path, CachePathNative);
   // Walk all of the files within this directory.
   for (sys::fs::directory_iterator File(CachePathNative, EC), FileEnd;
        File != FileEnd && !EC; File.increment(EC)) {
-    // Ignore any files not beginning with the string "llvmcache-". This
+    // Ignore any files not beginning with the prefix string. This
     // includes the timestamp file as well as any files created by the user.
     // This acts as a safeguard against data loss if the user specifies the
     // wrong directory as their cache directory.
-    if (!sys::path::filename(File->path()).startswith("llvmcache-"))
+    if (!sys::path::filename(File->path()).startswith((Prefix + "-").str()))
       continue;
 
     // Look at this file. If we can't stat it, there's nothing interesting
     // there.
     ErrorOr<sys::fs::basic_file_status> StatusOrErr = File->status();
     if (!StatusOrErr) {
       LLVM_DEBUG(dbgs() << "Ignore " << File->path() << " (can't stat)\n");
       continue;