[Tooling] Use FixedCompilationDatabase when `compile_flags.txt` is found.

Summary:
This is an alternative to JSONCompilationDatabase for simple projects that
don't use a build system such as CMake.
(You can also drop one in ~, to make your tools use e.g. C++11 by default)

There's no facility for varying flags per-source-file or per-machine.
Possibly this could be accommodated backwards-compatibly using cpp, but even if
not the simplicity seems worthwhile for the cases that are addressed.

Tested with clangd, works great! (requires clangd restart)

Reviewers: klimek

Subscribers: ilya-biryukov, cfe-commits

Differential Revision: https://reviews.llvm.org/D39799

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@317777 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 19 insertions, 0 deletions

diff --git a/test/Tooling/Inputs/fixed-header.h b/test/Tooling/Inputs/fixed-header.h
new file mode 100644
index 0000000000..4ce318f3a4
--- /dev/null
+++ b/test/Tooling/Inputs/fixed-header.h
@@ -0,0 +1 @@
+#define SECRET_SYMBOL 1
diff --git a/test/Tooling/fixed-database.cpp b/test/Tooling/fixed-database.cpp
new file mode 100644
index 0000000000..e0cdb1e51e
--- /dev/null
+++ b/test/Tooling/fixed-database.cpp
@@ -0,0 +1,18 @@
+// RUN: rm -rf %t
+// RUN: mkdir -p %t/Src
+// RUN: cp "%s" "%t/Src/test.cpp"
+// RUN: mkdir -p %t/Include
+// RUN: cp "%S/Inputs/fixed-header.h" "%t/Include/"
+// -I flag is relative to %t (where compile_flags is), not Src/.
+// RUN: echo '-IInclude/' >> %t/compile_flags.txt
+// RUN: echo "-Dklazz=class" >> %t/compile_flags.txt
+// RUN: echo '-std=c++11' >> %t/compile_flags.txt
+// RUN: clang-check "%t/Src/test.cpp" 2>&1
+// RUN: not clang-check "%s" 2>&1 | FileCheck "%s" -check-prefix=NODB
+
+// NODB: unknown type name 'klazz'
+klazz F{};
+
+// NODB: 'fixed-header.h' file not found
+#include "fixed-header.h"
+static_assert(SECRET_SYMBOL == 1, "");