[clang][cas] Dump module cache key if it fails to load

If a module fails to load via fmodule-file-cache-key, dump out the
structured form of the key (compiler arguments, cas-fs/include-tree) in
the diagnostic. This makes it easier to triage such issues when only a
build log is available, since it can be used to figure out if the
command to produce the expected module was not run, or was run with the
wrong compiler arguments, or inputs. While the diagnostic message with
be "large" it is expected that these errors are rare and typically
implicate a bug in the compiler or in the build system rather than an
error the user is responsible for.

(cherry picked from commit a4c1397)

Author: benlangmuir

clang/lib/Frontend/CompilerInstance.cpp

@@ -24,6 +24,7 @@
 #include "clang/Config/config.h"
 #include "clang/Frontend/CASDependencyCollector.h"
 #include "clang/Frontend/ChainedDiagnosticConsumer.h"
+#include "clang/Frontend/CompileJobCacheKey.h"
 #include "clang/Frontend/CompileJobCacheResult.h"
 #include "clang/Frontend/FrontendAction.h"
 #include "clang/Frontend/FrontendActions.h"
@@ -2369,10 +2370,16 @@ static bool addCachedModuleFileToInMemoryCache(
   if (!Value || !*Value) {
     auto Diag = Diags.Report(diag::err_cas_cannot_get_module_cache_key)
                 << CacheKey << Provider;
-    if (!Value)
+    if (!Value) {
       Diag << Value.takeError();
-    else
-      Diag << "no such entry in action cache";
+    } else {
+      std::string ErrStr("no such entry in action cache; expected compile:\n");
+      llvm::raw_string_ostream Err(ErrStr);
+      if (auto E = printCompileJobCacheKey(CAS, *ID, Err))
+        Diag << std::move(E);
+      else
+        Diag << Err.str();
+    }
     return true;
   }
   auto ValueRef = CAS.getReference(**Value);

clang/test/CAS/fmodule-file-cache-key-errors.c

@@ -28,18 +28,48 @@
 
 // BAD_KEY: error: CAS cannot load module with key 'KEY' from -fmodule-file-cache-key: invalid cas-id 'KEY'
 
+// RUN: echo -n '-fmodule-file-cache-key=PATH=' > %t/bad_key2.rsp
+// RUN: cat %t/casid >> %t/bad_key2.rsp
+
+// RUN: not %clang_cc1 -triple x86_64-apple-macos11 \
+// RUN:   -fmodules -fno-implicit-modules \
+// RUN:   @%t/bad_key2.rsp \
+// RUN:   -fsyntax-only %t/tu.c \
+// RUN:   -fcas-path %t/cas -faction-cache-path %t/cache -fcas-fs @%t/casid \
+// RUN:   -fcache-compile-job -Rcompile-job-cache &> %t/bad_key2.txt
+// RUN: cat %t/bad_key2.txt | FileCheck %s -check-prefix=BAD_KEY2
+
+// BAD_KEY2: error: CAS cannot load module with key '{{.*}}' from -fmodule-file-cache-key: cas object is not a valid cache key
+
+// == Build A
+
+// RUN: %clang_cc1 -triple x86_64-apple-macos11 \
+// RUN:   -fmodules -fmodule-name=A -fno-implicit-modules \
+// RUN:   -emit-module %t/module.modulemap -o %t/A.pcm \
+// RUN:   -fcas-path %t/cas -faction-cache-path %t/cache -fcas-fs @%t/casid \
+// RUN:   -fcache-compile-job -Rcompile-job-cache &> %t/A.out.txt
+// RUN: cat %t/A.out.txt | FileCheck %s --check-prefix=CACHE-MISS
+// CACHE-MISS: remark: compile job cache miss
+// RUN: cat %t/A.out.txt | sed -E "s:^.*cache [a-z]+ for '([^']+)'.*$:\1:" > %t/A.key
+
+// == Try to import A with a different action cache, simulating a missing module
+
 // RUN: echo -n '-fmodule-file-cache-key=PATH=' > %t/not_in_cache.rsp
-// RUN: cat %t/casid >> %t/not_in_cache.rsp
+// RUN: cat %t/A.key >> %t/not_in_cache.rsp
 
 // RUN: not %clang_cc1 -triple x86_64-apple-macos11 \
 // RUN:   -fmodules -fno-implicit-modules \
 // RUN:   @%t/not_in_cache.rsp \
 // RUN:   -fsyntax-only %t/tu.c \
-// RUN:   -fcas-path %t/cas -faction-cache-path %t/cache -fcas-fs @%t/casid \
+// RUN:   -fcas-path %t/cas -faction-cache-path %t/cache_2 -fcas-fs @%t/casid \
 // RUN:   -fcache-compile-job -Rcompile-job-cache &> %t/not_in_cache.txt
-// RUN: cat %t/not_in_cache.txt | FileCheck %s -check-prefix=NOT_IN_CACHE
+// RUN: cat %t/not_in_cache.txt | FileCheck %s -check-prefix=NOT_IN_CACHE -DPREFIX=%/t
 
-// NOT_IN_CACHE: error: CAS cannot load module with key '{{.*}}' from -fmodule-file-cache-key: no such entry in action cache
+// NOT_IN_CACHE: error: CAS cannot load module with key '{{.*}}' from -fmodule-file-cache-key: no such entry in action cache; expected compile:
+// NOT_IN_CACHE: command-line:
+// NOT_IN_CACHE:   -cc1
+// NOT_IN_CACHE: filesystem:
+// NOT_IN_CACHE:   file llvmcas://{{.*}} [[PREFIX]]/A.h
 
 //--- module.modulemap
 module A { header "A.h" }