include_graphics fails with '~' home directory shorthand

[RoyalTS]

include_graphics apparently fails on Mac when I specify a path using the ~ shorthand for the user home directory.

```{r}
knitr::include_graphics('~/myProject/out/figures/2017-06-23/sample_size_all.pdf')
```

gives

[pandoc warning] Could not find image `~/myProject/out/figures/2017-06-23/sample_size_all.pdf', skipping...

upon knitting. The following works, in contrast:

```{r}
knitr::include_graphics('/Users/myUsername/myProject/out/figures/2017-06-23/sample_size_all.pdf')
```

[yihui]

Absolute paths like this is almost always a very bad idea. Please use relative paths instead for the sake of portability.

[RoyalTS]

I am well aware that it's usually a good idea to use paths relative to the location of the document. In this case, however, precisely for reasons of portability I've specified all paths relative to project root using the here package, which spits out absolute paths. The above is just a demonstration that some absolute paths don't seem to work for include_graphics.

[yihui]

I guess it is not the responsibility of knitr::include_graphics() to process the path. This function takes whatever paths you pass to it. It is Pandoc that failed to recognize ~. If this issue has to be fixed, I'd recommend the here package to do either of the following things:

• normalizePath() or path.expand();

• or return a relative path (at least provide an option to return a relative path).

I have my reserved opinions about here. I see its point, but I don't think this nasty problem of file paths really has a perfect solution.

[jzadra]

THe odd thing is that paths with '~' work for ioslides, but not html/doc documents, and both use pandoc. Couldn't include_graphics() just expand the path itself to avoid this error?

[yihui]

It could. It is just that I prefer fixing the disease instead of the symptoms. In this case, it is not the fault of include_graphics(). Either the user or the here package could do path.expand(). If I do it in include_graphics(), I have no idea whether it is going to have other undesired effects.

ioslides is different with all other output formats. It is based on a custom Lua writer. That is probably why Pandoc wouldn't complain about the path.

[jzadra]

Gotcha, thanks for the response and for the awesome package!

[github-actions]

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