[clang] NFCI: [clang][deps] Simplify handling of main TU context hash (PR #141966)

[Jan Svoboda via cfe-commits]

https://github.com/jansvoboda11 created https://github.com/llvm/llvm-project/pull/141966

Instead of handling the context hash in a preprocessor callback on each file change, do it once at the end of the scan.

>From 26d8a1828e201447fb3cba5ba4258a4b282a79cc Mon Sep 17 00:00:00 2001
From: Jan Svoboda <jan_svoboda at apple.com>
Date: Tue, 27 May 2025 10:17:54 -0700
Subject: [PATCH] [clang][deps] Simplify handling of main TU context hash

---
 .../Tooling/DependencyScanning/ModuleDepCollector.h    |  2 --
 .../Tooling/DependencyScanning/ModuleDepCollector.cpp  | 10 +++-------
 2 files changed, 3 insertions(+), 9 deletions(-)

diff --git a/clang/include/clang/Tooling/DependencyScanning/ModuleDepCollector.h b/clang/include/clang/Tooling/DependencyScanning/ModuleDepCollector.h
index 06717a64c9a78..ad452a3faa73c 100644
--- a/clang/include/clang/Tooling/DependencyScanning/ModuleDepCollector.h
+++ b/clang/include/clang/Tooling/DependencyScanning/ModuleDepCollector.h
@@ -325,8 +325,6 @@ class ModuleDepCollector final : public DependencyCollector {
   const ArrayRef<StringRef> StableDirs;
   /// Path to the main source file.
   std::string MainFile;
-  /// Hash identifying the compilation conditions of the current TU.
-  std::string ContextHash;
   /// Non-modular file dependencies. This includes the main source file and
   /// textually included header files.
   std::vector<std::string> FileDeps;
diff --git a/clang/lib/Tooling/DependencyScanning/ModuleDepCollector.cpp b/clang/lib/Tooling/DependencyScanning/ModuleDepCollector.cpp
index 45901cbcedcb7..a6693e5a870e2 100644
--- a/clang/lib/Tooling/DependencyScanning/ModuleDepCollector.cpp
+++ b/clang/lib/Tooling/DependencyScanning/ModuleDepCollector.cpp
@@ -632,13 +632,6 @@ void ModuleDepCollectorPP::LexedFileChanged(FileID FID,
   if (Reason != LexedFileChangeReason::EnterFile)
     return;
 
-  // This has to be delayed as the context hash can change at the start of
-  // `CompilerInstance::ExecuteAction`.
-  if (MDC.ContextHash.empty()) {
-    MDC.ContextHash = MDC.ScanInstance.getInvocation().getModuleHash();
-    MDC.Consumer.handleContextHash(MDC.ContextHash);
-  }
-
   SourceManager &SM = MDC.ScanInstance.getSourceManager();
 
   // Dependency generation really does want to go all the way to the
@@ -720,6 +713,9 @@ void ModuleDepCollectorPP::EndOfMainFile() {
   for (const Module *M : MDC.DirectModularDeps)
     handleTopLevelModule(M);
 
+  MDC.Consumer.handleContextHash(
+      MDC.ScanInstance.getInvocation().getModuleHash());
+
   MDC.Consumer.handleDependencyOutputOpts(*MDC.Opts);
 
   if (MDC.Service.getFormat() == ScanningOutputFormat::P1689)