[clang] [clang][DepScan] Allow ModuleDep to be const (PR #132968)

[Cyndy Ishida via cfe-commits]

https://github.com/cyndyishida created https://github.com/llvm/llvm-project/pull/132968

This type can be exposed from C APIs, where instantiations of this type are not expected to mutate after creation. To support this, mark the lazy computation of build arguments mutable, as that is not intended to otherwise mutate the state of these objects.


This was reviewed separately by @jansvoboda11

>From 278b2145d37a27f973c8c41a97b1a6dcf0fd5235 Mon Sep 17 00:00:00 2001
From: Cyndy Ishida <cyndy_ishida at apple.com>
Date: Tue, 11 Mar 2025 13:14:55 -0700
Subject: [PATCH] [clang][DepScan] Allow ModuleDep to be const

* Mark the lazy computation of build arguments mutable. As that is not
  intended to otherwise mutate the state of the object.
---
 .../clang/Tooling/DependencyScanning/ModuleDepCollector.h    | 5 +++--
 clang/lib/Tooling/DependencyScanning/ModuleDepCollector.cpp  | 4 +++-
 2 files changed, 6 insertions(+), 3 deletions(-)

diff --git a/clang/include/clang/Tooling/DependencyScanning/ModuleDepCollector.h b/clang/include/clang/Tooling/DependencyScanning/ModuleDepCollector.h
index 422202caddfd4..ed150b467e3a1 100644
--- a/clang/include/clang/Tooling/DependencyScanning/ModuleDepCollector.h
+++ b/clang/include/clang/Tooling/DependencyScanning/ModuleDepCollector.h
@@ -153,7 +153,7 @@ struct ModuleDeps {
 
   /// Get (or compute) the compiler invocation that can be used to build this
   /// module. Does not include argv[0].
-  const std::vector<std::string> &getBuildArguments();
+  const std::vector<std::string> &getBuildArguments() const;
 
 private:
   friend class ModuleDepCollector;
@@ -166,7 +166,8 @@ struct ModuleDeps {
   /// including transitive dependencies.
   std::vector<std::string> FileDeps;
 
-  std::variant<std::monostate, CowCompilerInvocation, std::vector<std::string>>
+  mutable std::variant<std::monostate, CowCompilerInvocation,
+                       std::vector<std::string>>
       BuildInfo;
 };
 
diff --git a/clang/lib/Tooling/DependencyScanning/ModuleDepCollector.cpp b/clang/lib/Tooling/DependencyScanning/ModuleDepCollector.cpp
index d715ef874e002..364f156566855 100644
--- a/clang/lib/Tooling/DependencyScanning/ModuleDepCollector.cpp
+++ b/clang/lib/Tooling/DependencyScanning/ModuleDepCollector.cpp
@@ -31,7 +31,9 @@ void ModuleDeps::forEachFileDep(llvm::function_ref<void(StringRef)> Cb) const {
   }
 }
 
-const std::vector<std::string> &ModuleDeps::getBuildArguments() {
+const std::vector<std::string> &ModuleDeps::getBuildArguments() const {
+  // FIXME: this operation is not thread safe and is expected to be called
+  // on a single thread. Otherwise it should be protected with a lock.
   assert(!std::holds_alternative<std::monostate>(BuildInfo) &&
          "Using uninitialized ModuleDeps");
   if (const auto *CI = std::get_if<CowCompilerInvocation>(&BuildInfo))