[clang] [clang][DependencyScanning] Adding a test that exercies the async-scanning code path (PR #211402)

[Qiongsi Wu via cfe-commits]

https://github.com/qiongsiwu created https://github.com/llvm/llvm-project/pull/211402

This PR adds a test that exercises the async-scanning code path to sanity check that async-scanning generates identical results as TU scanning.

---

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>From c2977443dd1b5156092afce6189fad39da14a648 Mon Sep 17 00:00:00 2001
From: Qiongsi Wu <qiongsi_wu at apple.com>
Date: Tue, 21 Jul 2026 14:02:51 -0700
Subject: [PATCH] Adding a test that exercies the async-scanning code path.

---
 clang/test/ClangScanDeps/modules-async-scan.c | 65 +++++++++++++++++++
 1 file changed, 65 insertions(+)
 create mode 100644 clang/test/ClangScanDeps/modules-async-scan.c

diff --git a/clang/test/ClangScanDeps/modules-async-scan.c b/clang/test/ClangScanDeps/modules-async-scan.c
new file mode 100644
index 0000000000000..f6dc3d15100b2
--- /dev/null
+++ b/clang/test/ClangScanDeps/modules-async-scan.c
@@ -0,0 +1,65 @@
+// Verify that dependency scanning produces identical results with and without
+// -async-scan-modules so we exercise the async scan code path.
+
+// RUN: rm -rf %t
+// RUN: split-file %s %t
+// RUN: sed -e "s|DIR|%/t|g" %t/cdb.json.in > %t/cdb.json
+
+// RUN: clang-scan-deps -compilation-database %t/cdb.json -j 1 \
+// RUN:   -format experimental-full -mode preprocess-dependency-directives \
+// RUN:   > %t/sync.json
+// RUN: clang-scan-deps -compilation-database %t/cdb.json -j 1 -async-scan-modules \
+// RUN:   -format experimental-full -mode preprocess-dependency-directives \
+// RUN:   > %t/async.json
+
+// RUN: diff -u %t/sync.json %t/async.json
+
+// Sanity-check that the scan computed the correct module graph.
+// RUN: FileCheck %s < %t/sync.json
+// CHECK-DAG: "name": "A"
+// CHECK-DAG: "name": "B"
+// CHECK-DAG: "name": "C"
+
+//--- cdb.json.in
+
+[{
+  "directory": "DIR",
+  "command": "clang -c DIR/main.c -IDIR -fmodules -fmodules-cache-path=DIR/module-cache -fimplicit-modules -fimplicit-module-maps",
+  "file": "DIR/main.c"
+}]
+
+//--- module.modulemap
+
+module A {
+  header "a.h"
+}
+
+module B {
+  header "b.h"
+}
+
+module C {
+  header "c.h"
+}
+
+//--- a.h
+
+#include "b.h"
+void a(void);
+
+//--- b.h
+
+void b(void);
+
+//--- c.h
+
+void c(void);
+
+//--- main.c
+
+#include "a.h"
+#include "c.h"
+void m(void) {
+  a();
+  c();
+}