[clang] [clang][DependencyScanning] Implementation of `CompilerInstanceWithContext` to Improve By-Name Queries (PR #164345)

[Qiongsi Wu via cfe-commits]

================
@@ -705,3 +707,185 @@ bool DependencyScanningAction::runInvocation(
 
   return Result;
 }
+
+const std::string CompilerInstanceWithContext::FakeFileBuffer =
+    std::string(MAX_NUM_NAMES, ' ');
+
+llvm::Error CompilerInstanceWithContext::initialize() {
+  std::tie(OverlayFS, CommandLine) = initVFSForByNameScanning(
+      Worker.BaseFS, CommandLine, CWD, "ScanningByName");
+
+  DiagPrinterWithOS =
+      std::make_unique<TextDiagnosticsPrinterWithOutput>(CommandLine);
+  DiagEngineWithCmdAndOpts = std::make_unique<DignosticsEngineWithDiagOpts>(
+      CommandLine, OverlayFS, DiagPrinterWithOS->DiagPrinter);
+
+  std::tie(Driver, Compilation) = buildCompilation(
+      CommandLine, *DiagEngineWithCmdAndOpts->DiagEngine, OverlayFS);
+
+  if (!Compilation) {
+    return llvm::make_error<llvm::StringError>("Failed to build compilation",
+                                               llvm::inconvertibleErrorCode());
+  }
+
+  const driver::Command &Command = *(Compilation->getJobs().begin());
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qiongsiwu wrote:

Added an assert to catch the case. I don't think this is an error case because I assume if a `Compilation` instance is successfully built, we will have at least one job. 

https://github.com/llvm/llvm-project/pull/164345