Xcode: emitted warnings won't highlight character/column

[jhauberg]

I've been unable to get Xcode to properly highlight the proper parts of text indicated by an emitted warning.

For example, this is a warning that is treated and displayed as a warning in Xcode. However, it has both line and column index, but it seems the character index is being ignored completely.

So, raw output from comply:

/absolute/path/to/src/model/deck.c:9:22: warning: Unused symbol 'ceil' should not be listed as needed. [symbol-listed-not-needed]

This is what you get if you 'copy' the displayed warning from the build log:

/absolute/path/to/src/model/deck.c:9: Unused symbol 'ceil' should not be listed as needed. [symbol-listed-not-needed]

Notice how the warning: and column index has been stripped.

I've also tried emulating warnings/errors as reported by the compiler, which could look like:

/absolute/path/to/src/model/deck.c:29:5: error: use of undeclared identifier 'what'
    what
    ^

In Xcode, above looks like:

Notice the little red line under 'w'.

Now, if you take above generated error and put it into a run script:

echo "/absolute/path/to/src/model/deck.c:29:5: error: use of undeclared identifier 'what'"
echo "    what"
echo "    ^"
exit 1

Suddenly, only the line is being highlighted:

So I guess perhaps this is a security measure that won't let scripts do all that jazz?

EDIT:
So i've just tried making a fresh Xcode command-line project, and surprisingly, it actually works as expected:

Still haven't figured out how to add fix-it bubbles or underline parts (e.g. using `~~~` and `^`).

Again, emulating output as seen from compiler does not seem to work, e.g.:

```
/long/path/to/file.swift:57:17: warning: initialization of variable 'x' was never used; consider replacing with assignment to '_' or removing it
            var x = 0
            ~~~~^
            _
```

Emulated for fresh project:

```
echo "/full/path/main.c:13:1: warning: Replace int with var"
echo "int main(int argc, const char * argv[]) {"
echo "^~~"
echo "var"
```

This just shows a regular old warning, ignoring underlining and fix-it option:

![screen shot 2018-01-24 at 11 50 49](https://user-images.githubusercontent.com/1360637/35328511-e4e82526-00fc-11e8-902e-6c73e25c13db.png)

Again, i'm uncertain that scripts are even allowed to do this. But who knows?

Related, changing build system from standard to preview also cause character index to be ignored:

![screen shot 2018-01-24 at 11 55 32](https://user-images.githubusercontent.com/1360637/35328742-a389f964-00fd-11e8-9ccc-837a346b339e.png)
![screen shot 2018-01-24 at 11 55 22](https://user-images.githubusercontent.com/1360637/35328752-addf5602-00fd-11e8-99d9-5ad3988df461.png)

[jhauberg]

Relevant/related:

https://clang.llvm.org/diagnostics.html
realm/SwiftLint#27

[jhauberg]

It's unlikely that we can do more about this. Fix-Its and underlining is likely always going to be reserved for the built-in processes (compiler, analyzer) in Xcode.

The ClangReporter could be extended to support this stuff, and it may be worthwhile for other IDEs/editors (SublimeText?), but for now i'm closing this.