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[driver] add a new option `-gen-cdb-fragment-path` to emit a fragment of a compilation database for each compilation

Authored by arphaman on Aug 21 2019, 1:46 PM.



This patch adds a new option called -gen-cdb-fragment-path to the driver, which can be used to specify a directory path to which clang can emit a fragment of a CDB for each compilation it needs to invoke.

The CDB fragment is emitted into a unique file in the specified directory. It contains the -cc1 clang invocation in its command. The file itself is actually a valid standalone CDB (if you disregard the not yet well supported -cc1 innovation by the CDB, which I'll fix). To load the full CDB that can be emitted during a build, I'm going to add a new CDB reader from a directory that reads all fragments and aggregates them into one CDB in a follow-up patch.

This is useful to setup verification infrastructure for clang-scan-deps for some projects that don't have a way of constructing a CDB from their build.

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arphaman created this revision.Aug 21 2019, 1:46 PM
Herald added a project: Restricted Project. · View Herald TranscriptAug 21 2019, 1:46 PM
jkorous added inline comments.Aug 21 2019, 2:20 PM
1044 ↗(On Diff #216466)

IIUC this feature might end up being used from some test script. I'm wondering - what would happen had the argument been an empty string?

clang -c foo.c -gen-cdb-fragment-path ""
4868 ↗(On Diff #216466)

I am just wondering whether we shouldn't notice user about failures, possibly with some error message.

4896 ↗(On Diff #216466)

It feels like this might have been already implemented somewhere else.

Couldn't we use for example llvm::yaml::escape()?

How does it relate to the -MJ option?

How does it relate to the -MJ option?

Ah, I wasn't aware that such option existed. I should use it instead.

arphaman updated this revision to Diff 216717.Aug 22 2019, 2:17 PM

Reimplement the new option on top of -MJ. -MJ is still the preferred option if both are specified.

@jkorous I addressed your comments as well ("" directory is now allowed, error is reported, existing escape used).

jkorous added inline comments.Aug 22 2019, 6:43 PM

Do we still need this now?


Just to make sure - the error different on purpose here?


I'm not familiar with intended lifecycle of CompilationDatabase member. Just to make sure - we need neither to preserve the original value nor reset the stream after we're done here (as in - nobody is going to write anything after we're done here), right?

jkorous added inline comments.Aug 22 2019, 6:46 PM

BTW this looks kind of funny const InputInfo &Output, const InputInfo &Input.

arphaman updated this revision to Diff 216898.Aug 23 2019, 10:40 AM

Address review comments.

arphaman marked 5 inline comments as done.Aug 23 2019, 10:42 AM
arphaman added inline comments.

No, the CWD should actually be read in DumpCompilationDatabase. I updated that method.


Not really needed I guess, I reused the error.


Yes, we should either preserve or not reset the stream once it's created. Multiple clang invocations can be constructed from one driver run, so we want to keep the stream open while the driver is running.


Yes, that's unfortunate type naming in Clang :(

jkorous accepted this revision.Aug 23 2019, 6:09 PM
This revision is now accepted and ready to land.Aug 23 2019, 6:09 PM
This revision was automatically updated to reflect the committed changes.
arphaman marked an inline comment as done.