Improve the display of error messages

[ndmitchell]

Currently you might get:

Error when running Shake build system:
* Main.exe
* Development/Shake/Internal/Shake.o
* Development/Shake/Internal/Shake.o Development/Shake/Internal/Shake.hi
here
CallStack (from HasCallStack):
  error, called at src\Test\Self.hs:65:9 in main:Test.Self

Straw man proposal:

Error when running Shake build system:
* Starting from: Main.exe
  With rule declared at src\Test\Self.hs:45
* Depends on: Development/Shake/Internal/Shake.o
  With rule declared at src\Test\Self:56
* Depends on: Development/Shake/Internal/Shake.o Development/Shake/Internal/Shake.hi
  With rule declared at src\Test\Self:72
* Which raised the error:
here
CallStack (from HasCallStack):
  error, called at src\Test\Self.hs:65:9 in main:Test.Self

Suggestions for tweaks most welcome, e.g. from @snowleopard who got confused by this in snowleopard/hadrian#562.

[snowleopard]

@ndmitchell I like this! Definitely an improvement.

Dancing slashes add a bit of distraction -- can you point them in one direction?

[ndmitchell]

Good idea about the slashes

[ndmitchell]

It's now improved, but still not perfect:

*Test> :main errors chain.3
Longest file modification time lag was 3ms
## BUILD errors chain.3
Error when running Shake build system:
  at src/Test/Type.hs:51:46-55:
  at src/Test/Type.hs:51:46-55:
* Depends on: chain.3
  at src/Development/Shake/Internal/Derived.hs:94:5-15:
* Depends on: chain.2
* Raised the exception:
err_chain
CallStack (from HasCallStack):
  error, called at src\Test\Errors.hs:91:30 in main:Test.Errors

[ndmitchell]

The duplicate at lines at the start were valid - want calls both action (is tracked) and apply (is tracked). I have the stack omit them though so it looks prettier.

[snowleopard]

Thanks! I'm sure this will help.