[PATCH] D23532: [LibTooling] Allow compilation database to explicitly specify compilation database file and source root

[Zachary Turner via cfe-commits]

zturner created this revision.
zturner added a reviewer: cfe-commits.
zturner added subscribers: klimek, alexfh, djasper.

Allow explicit specification of a compilation database file and source root.

While trying to create a compilation database test for D23455, I ran into the problem that compilation database tests require a command shell, evidenced by the fact that at the top of `clang-tidy-run-with-database-cpp` contains the line `REQUIRES: SHELL`.  This makes it impossible to write the test that was requested in D23455 (not to mention it means the existing test is not running on Windows either).

I solve this by introducing a new command line parameter and slightly enhancing the functionality of an existing one, detailed below:

1. There was no way to specify an arbitrary compilation database.  At best you could specify the directory of a compilation database, but it would still be forced to look for `compile_commands.json`.  This is an inflexible design when you want to have multiple tests which each use their own compilation database.  You could put them in different folders and call each one `compile_commands.json`, but that leads to many different directories with only one file, which is kind of silly.

The `-p` option let you specify a build path, which would be the folder where a compilation database existed, but it did not let you specify a *specific file* to use as a compilation database.  I improved expanded this behavior of this option to check if the specified path is a regular file or a directory.  If it is a regular file it doesn't search for a compilation database, and instead just uses the file you specify.  The nice thing about this is that now we can put many compilation databases for various tests in the same directory, and have the run line of the test reference the exact compilation database needed for the test.

2. Instead of a "real" compilation database, the test consisted of a template.  And the test used shell in order to invoke `sed` to modify the template so that the files and directories would be correct.  So the test would output the modified template into the CMake output directory, and then it had to use more shell commands to copy the source files over to the CMake output directory so that they would be in the right hierarchy in order to be found by the relative paths written to the compilation database.

In order to remove the dependency on shell, we need a way to reference the source files in their original location in the source tree, and not require them to be copied to the output tree.  To do this I introduced a new command line option `-r` that lets you specify the root at which relative paths are resolved against.  

These two things combined eliminate the need to modify the compilation database with `sed` and write it to the output folder because we can write *actual* source code on disk and check it in for the tests, and the compilation database can refer to these files using actual relative paths.  Then because of #1, the run line can point directly to the compilation database in question.

I re-wrote the compilation database test to use this new method, and it now no longer depends on shell.  I will upload the re-written test in a separate patch since I can't do cross-repo diffs.

https://reviews.llvm.org/D23532

Files:
  include/clang/Tooling/CompilationDatabase.h
  include/clang/Tooling/JSONCompilationDatabase.h
  lib/Tooling/CommonOptionsParser.cpp
  lib/Tooling/CompilationDatabase.cpp
  lib/Tooling/JSONCompilationDatabase.cpp
  lib/Tooling/Tooling.cpp

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