Add extensions via function in upgrade.R

[mgirlich]

Fixes #274.

• I'm not sure whether we also need patch files for every extension
• The current naming for loading extensions is in my opinion a bit confusing. initExtension() to load the math functions and initRegExp() to load the regular expressions. I think it would be nice to always have "extension" somewhere in the name.
• I didn't manage to compile the ICU extension. It always complained "'unicode/utypes.h' file not found" even though I installed icu4c with homebrew... (also see stackoverflow)

db <- RSQLite::datasetsDb()
RSQLite::initSeries(db)
RSQLite::dbGetQuery(db, "SELECT value FROM generate_series(5,20,5);")
#>   value
#> 1     5
#> 2    10
#> 3    15
#> 4    20

^{Created on 2021-11-03 by the reprex package (v2.0.1)}

[krlmlr]

Thanks for working on this! I think we can soft-deprecate initExtension() in favor of something clearer.

sqlite is plain C, do we need to compile differently with extensions that are C++?

[krlmlr]

Another thing: should extensions live in src/vendor/extensions, with different compilation rules?

[mgirlich]

I put the extensions in their own folder src/vendor/extensions as suggested. They now have their own compilation rules in MAKEVARS. I don't know much about make files so you might have some improvement suggestions.
Currently, the MAKEVARS file is changed by hand for every extension but this could also be automated.

• I am not sure what the regexp.patch file is for. Do we also need to patch the other extension files?
• Should we compile the extensions as shared library? At least that's what it says on https://www.sqlite.org/loadext.html? I don't know what the pros and cons would be.

[krlmlr]

Thanks for working on this. What are the compilation failures in the CSV extension about? Should we remove it for now and investigate separately?

[krlmlr]

I tweaked a bit. It's weird that compilation of the csv extension works on some systems, is it relying on system header files? That would be undesirable, we're vendoring everything.

Let's avoid the extra complexity of shared libraries.

[krlmlr]

Added an explicit include path, let's see if the build behaves now.

Instead of multiple initXXX() functions, should we keep only initExtensions() and add a name argument? The default extension would be "math", the others would be called by their short name. I don't mind soft-deprecating initRegExp() .

[krlmlr]

Thanks!