[clang] [clang][DependencyScanning] Reset options generated for named module compilations. (PR #161486)

[Naveen Seth Hanig via cfe-commits]

https://github.com/naveen-seth created https://github.com/llvm/llvm-project/pull/161486

The driver-generated -cc1 command-lines for C++ named module inputs introduce some command-line options which affect the canonical module build command (and therefore the context hash).
This resets those options.

>From 52a54eeb0bccb871c7addcf3236f40ffb7a226a9 Mon Sep 17 00:00:00 2001
From: Naveen Seth Hanig <naveen.hanig at outlook.com>
Date: Wed, 1 Oct 2025 03:51:58 +0200
Subject: [PATCH] [clang][DependencyScanning] Reset options generated for named
 module compilations.

The driver-generated -cc1 command-lines for C++ named module inputs
introduce some command-line options which affect the canonical module
build command (and therefore the context hash).
This resets those options.
---
 .../DependencyScanning/ModuleDepCollector.cpp |   4 +
 ...modules-context-hash-from-named-module.cpp | 111 ++++++++++++++++++
 2 files changed, 115 insertions(+)
 create mode 100644 clang/test/ClangScanDeps/modules-context-hash-from-named-module.cpp

diff --git a/clang/lib/Tooling/DependencyScanning/ModuleDepCollector.cpp b/clang/lib/Tooling/DependencyScanning/ModuleDepCollector.cpp
index d67178c153e88..a117bec0d656e 100644
--- a/clang/lib/Tooling/DependencyScanning/ModuleDepCollector.cpp
+++ b/clang/lib/Tooling/DependencyScanning/ModuleDepCollector.cpp
@@ -263,6 +263,10 @@ makeCommonInvocationForModuleBuild(CompilerInvocation CI) {
   // units.
   CI.getFrontendOpts().Inputs.clear();
   CI.getFrontendOpts().OutputFile.clear();
+  CI.getFrontendOpts().GenReducedBMI = false;
+  CI.getFrontendOpts().ModuleOutputPath.clear();
+  CI.getHeaderSearchOpts().ModulesSkipHeaderSearchPaths = false;
+  CI.getHeaderSearchOpts().ModulesSkipDiagnosticOptions = false;
   // LLVM options are not going to affect the AST
   CI.getFrontendOpts().LLVMArgs.clear();
 
diff --git a/clang/test/ClangScanDeps/modules-context-hash-from-named-module.cpp b/clang/test/ClangScanDeps/modules-context-hash-from-named-module.cpp
new file mode 100644
index 0000000000000..04148953b5683
--- /dev/null
+++ b/clang/test/ClangScanDeps/modules-context-hash-from-named-module.cpp
@@ -0,0 +1,111 @@
+// Check that the driver-generated command line options for  C++ module inputs
+// do not unexpectedly change the context hash of imported Clang modules
+// compared to the command line for an otherwise equal non-module input.
+
+// RUN: rm -rf %t
+// RUN: split-file %s %t
+
+//--- main.cpp
+#include "root.h"
+import A;
+import B;
+
+auto main() -> int { return 1; }
+
+//--- A.cppm
+module;
+#include "root.h"
+export module A;
+
+//--- B.cppm
+module;
+#include "root.h"
+export module B;
+
+//--- module.modulemap
+module root { header "root.h" }
+
+//--- root.h
+// empty
+
+// RUN: %clang++ -std=c++23 -fmodules %t/main.cpp %t/A.cppm %t/B.cppm -fsyntax-only -fdriver-only -MJ %t/deps.json
+// RUN: sed -e '1s/^/[/' -e '$s/,$/]/' %t/deps.json | sed 's:\\\\\?:/:g' > %t/compile_commands.json
+// RUN: clang-scan-deps -compilation-database=%t/compile_commands.json -format experimental-full > %t/result.json
+// RUN: cat %t/result.json
+
+// RUN: cat %t/result.json | sed 's:\\\\\?:/:g' | FileCheck %s -DPREFIX=%/t
+
+// CHECK:      {
+// CHECK-NEXT:   "modules": [
+// CHECK-NEXT:     {
+// CHECK-NEXT:       "clang-module-deps": [],
+// CHECK-NEXT:       "clang-modulemap-file": "[[PREFIX]]/module.modulemap",
+// CHECK:            "context-hash": "[[HASH_ROOT:.*]]",
+// CHECK-NEXT:       "file-deps": [
+// CHECK-NEXT:         "[[PREFIX]]/module.modulemap",
+// CHECK-NEXT:         "[[PREFIX]]/root.h"
+// CHECK-NEXT:       ],
+// CHECK-NEXT:       "link-libraries": [],
+// CHECK-NEXT:       "name": "root"
+// CHECK-NEXT:     }
+// CHECK-NEXT:   ],
+// CHECK-NEXT:   "translation-units": [
+// CHECK-NEXT:     {
+// CHECK-NEXT:       "commands": [
+// CHECK-NEXT:         {
+// CHECK-NEXT:           "clang-context-hash": "{{.*}}",
+// CHECK-NEXT:           "named-module-deps": [
+// CHECK-NEXT:             "A",
+// CHECK-NEXT:             "B"
+// CHECK-NEXT:           ],
+// CHECK-NEXT:           "clang-module-deps": [
+// CHECK-NEXT:             {
+// CHECK-NEXT:               "context-hash": "[[HASH_ROOT]]",
+// CHECK-NEXT:               "module-name": "root"
+// CHECK-NEXT:             }
+// CHECK-NEXT:           ],
+// CHECK:                "file-deps": [
+// CHECK-NEXT:             "[[PREFIX]]/main.cpp"
+// CHECK-NEXT:           ],
+// CHECK-NEXT:           "input-file": "[[PREFIX]]/main.cpp"
+// CHECK-NEXT:         }
+// CHECK-NEXT:       ]
+// CHECK-NEXT:     },
+// CHECK-NEXT:     {
+// CHECK-NEXT:       "commands": [
+// CHECK-NEXT:         {
+// CHECK-NEXT:           "clang-context-hash": "{{.*}}",
+// CHECK-NEXT:           "named-module": "A",
+// CHECK-NEXT:           "clang-module-deps": [
+// CHECK-NEXT:             {
+// CHECK-NEXT:               "context-hash": "[[HASH_ROOT]]",
+// CHECK-NEXT:               "module-name": "root"
+// CHECK-NEXT:             }
+// CHECK-NEXT:           ],
+// CHECK:                "file-deps": [
+// CHECK-NEXT:             "[[PREFIX]]/A.cppm"
+// CHECK-NEXT:           ],
+// CHECK-NEXT:           "input-file": "[[PREFIX]]/A.cppm"
+// CHECK-NEXT:         }
+// CHECK-NEXT:       ]
+// CHECK-NEXT:     },
+// CHECK-NEXT:     {
+// CHECK-NEXT:       "commands": [
+// CHECK-NEXT:         {
+// CHECK-NEXT:           "clang-context-hash": "{{.*}}",
+// CHECK-NEXT:           "named-module": "B",
+// CHECK-NEXT:           "clang-module-deps": [
+// CHECK-NEXT:             {
+// CHECK-NEXT:               "context-hash": "[[HASH_ROOT]]",
+// CHECK-NEXT:               "module-name": "root"
+// CHECK-NEXT:             }
+// CHECK-NEXT:           ],
+// CHECK:                "file-deps": [
+// CHECK-NEXT:             "[[PREFIX]]/B.cppm"
+// CHECK-NEXT:           ],
+// CHECK-NEXT:           "input-file": "[[PREFIX]]/B.cppm"
+// CHECK-NEXT:         }
+// CHECK-NEXT:       ]
+// CHECK-NEXT:     }
+// CHECK-NEXT:   ]
+// CHECK-NEXT: }