include filename in error: could not read file message

[jakobhellermann]

I was building a project with janet build mistakenly instead of jpm build and got

error: could not read file
  in file/read [src/core/io.c] on line 193
  in chunks [boot.janet] on line 3009, column 24
  in run-context [boot.janet] on line 2653, column 12
  in dofile [boot.janet] on line 3032, column 5
  in cli-main [boot.janet] on line 4645, column 17

as a result.

This isn't particularly helpful and it would be neat if the message included the name of the file it tried to read.

Looks like the error comes from

janet/src/core/io.c

Line 188 in 83e8aab

janet_panic("could not read file");

which only has access to a JanetFile, which doesn't include the filename, only a FILE*:

janet/src/include/janet.h

Lines 1248 to 1251 in 83e8aab

	struct JanetFile {
	FILE *file;
	int32_t flags;
	};

So possible solutions could be

1. store the filename the file was opened by in JanetFile
2. attempt to find the filename associated to the file descriptor. (could be /proc/self/fd/NNN or F_GETPATH or F_GETPATH or GetFileInformationByHandleEx on windows? would need to investigate)
   if this is in scope for janet

[strangepete]

Giving this the quick eyeball, I'm curious as to why 'build' is passing file/open in boot.janet and instead failing in fread; file/open at least returns the filename in the error.

Edit: oddly, when I type the same janet build I do in fact get a filename in the error:

error: could not find file build
  in dofile [boot.janet] on line 2966, column 5
  in cli-main [boot.janet] on line 4539, column 17

[sogaiu]

I think if one does jpm build at some point, then a build directory may get created. If subsequently one does janet build without removing the build directory, one may get:

$ janet build
error: could not read file
  in file/read [src/core/io.c] on line 193
  in chunks [boot.janet] on line 3009, column 24
  in run-context [boot.janet] on line 2653, column 12
  in dofile [boot.janet] on line 3032, column 5
  in cli-main [boot.janet] on line 4645, column 17

If the build directory doesn't exist:

$ rm -rf build && janet build
error: could not find file build
  in dofile [boot.janet] on line 3030, column 5
  in cli-main [boot.janet] on line 4645, column 17

[strangepete]

That is odd because I get the full error message regardless of the directories existence; on Windows 🤨

Edit: can confirm what you see on my linux box too

[strangepete]

https://stackoverflow.com/questions/42876210/c-fopen-opening-directories

Seems fopen has a quirk about detecting directories with write mode

---

The fopen() function will fail if:
[…]
[EISDIR] The named file is a directory and mode requires write access.

So if fopen is called with r instead of r+ it won't fail. I believe we just need a call to stat() on not-windows to confirm its a file