[clang][cas] Pass through LLVM_CAS_LOG env var to the depscan daemon

Ensure that the scanning daemon modifications to the CAS are captured
properly by the log.

(cherry picked from commit f6a775f)

Author: benlangmuir

clang/test/CAS/depscan-cas-log.c

@@ -0,0 +1,18 @@
+// Ensure both the first clang process and the daemon have logging enabled.
+// It's hard to check this exhaustively, but in practice if the daemon does not
+// enable logging there are currently zero records in the log.
+
+// RUN: rm -rf %t && mkdir %t
+// RUN: env LLVM_CACHE_CAS_PATH=%t/cas LLVM_CAS_LOG=1 %clang \
+// RUN:   -cc1depscan -fdepscan=daemon -fdepscan-include-tree -o - \
+// RUN:   -cc1-args -cc1 -triple x86_64-apple-macosx11.0.0 -emit-obj %s -o %t/t.o -fcas-path %t/cas
+// RUN: FileCheck %s --input-file %t/cas/v1.log
+
+// CHECK: [[PID1:[0-9]*]] {{[0-9]*}}: mmap '{{.*}}v8.index'
+// CHECK: [[PID1]] {{[0-9]*}}: create subtrie
+
+// CHECK: [[PID2:[0-9]*]] {{[0-9]*}}: mmap '{{.*}}v8.index'
+// Even a minimal compilation involves at least 9 records for the cache key.
+// CHECK-COUNT-9: [[PID2]] {{[0-9]*}}: create record
+
+// CHECK: [[PID1]] {{[0-9]*}}: close mmap '{{.*}}v8.index'

clang/tools/driver/cc1depscanProtocol.cpp

@@ -17,6 +17,7 @@
 #include "llvm/Support/Process.h"
 #include "llvm/Support/Signals.h"
 #include "llvm/Support/StringSaver.h"
+#include <cstdlib>
 
 #if LLVM_ON_UNIX
 #include <sys/socket.h> // FIXME: Unix-only. Not portable.
@@ -186,10 +187,19 @@ Expected<ScanDaemon> ScanDaemon::launchDaemon(StringRef BasePath,
     return llvm::errorCodeToError(std::error_code(EC, std::generic_category()));
 #endif
 
+  static constexpr const char *PassThroughEnv[] = {
+    "LLVM_CAS_LOG",
+  };
+  SmallVector<const char *> EnvP;
+  for (const char *Name : PassThroughEnv)
+    if (const char *Value = getenv(Name))
+      EnvP.push_back(Saver.save(llvm::Twine(Name) + "=" + Value).data());
+  EnvP.push_back(nullptr);
+
   ::pid_t Pid;
   int EC = ::posix_spawn(&Pid, Args[0], /*file_actions=*/nullptr, &Attrs,
                          const_cast<char **>(LaunchArgs.data()),
-                         /*envp=*/nullptr);
+                         const_cast<char **>(EnvP.data()));
   if (EC)
     return llvm::errorCodeToError(std::error_code(EC, std::generic_category()));