Improve message for broken markup.

[matthid]

This will be a collection of error messages to improve:

• Improve error message when Docs failed to build with an XML Parse error. #335

• Improve exception handling in literate programming #360

• Unresolved reference to log -> Print source (type/member) of the error. #366

• [ ]

  ![Some alt text 'Stream'](Content/images/test.jpg test-screen")
  

  Notice the missing ", this currently crashes with a cryptic message:

  System.ArgumentOutOfRangeException: Length cannot be less than zero.
  Parameter name: length
  at System.String.Substring(Int32 startIndex, Int32 length)
  at FSharp.Markdown.Parser.getLinkAndTitle(String _arg1) in c:\Projects\FSharp.Formatting\src\FSharp.Markdown\MarkdownParser.fs:line 27
  at [email protected](Unit unitVar) in c:\Projects\FSharp.Formatting\src\FSharp.Markdown\MarkdownParser.fs:line 223
  at [email protected](Unit unitVar0)
  at [email protected](Unit unitVar0)
  at Microsoft.FSharp.Collections.Generator.Microsoft-FSharp-Collections-Generator-Generator-1-get_Apply@432.Invoke(Unit unitVar0)
  at Microsoft.FSharp.Collections.Generator.appG[a](Generator`1 g)
  at Microsoft.FSharp.Collections.Generator.EnumeratorWrappingLazyGenerator`1.System-Collections-IEnumerator-MoveNext()
  at <StartupCode$FSharp-Core>[email protected](IEnumerable`1& next)
  at Microsoft.FSharp.Core.CompilerServices.GeneratedSequenceBase`1.MoveNextImpl()
  at Microsoft.FSharp.Collections.SeqModule.ToList[T](IEnumerable`1 source)
  at [email protected](Unit unitVar) in c:\Projects\FSharp.Formatting\src\FSharp.Markdown\MarkdownParser.fs:line 635
  at [email protected](Unit unitVar0)
  at [email protected](IEnumerable`1& next) in c:\Projects\FSharp.Formatting\src\FSharp.Markdown\MarkdownParser.fs:line 616
  at Microsoft.FSharp.Core.CompilerServices.GeneratedSequenceBase`1.MoveNextImpl()
  at Microsoft.FSharp.Collections.SeqModule.ToList[T](IEnumerable`1 source)
  at [email protected](IEnumerable`1& next) in c:\Projects\FSharp.Formatting\src\FSharp.Markdown\MarkdownParser.fs:line 615
  at Microsoft.FSharp.Core.CompilerServices.GeneratedSequenceBase`1.MoveNextImpl()
  at Microsoft.FSharp.Collections.SeqModule.ToList[T](IEnumerable`1 source)
  at FSharp.Markdown.Parser.formatTree@612(ParsingContext ctx, FSharpList`1 nodes) in c:\Projects\FSharp.Formatting\src\FSharp.Markdown\MarkdownParser.fs:line 613
  at [email protected](Unit unitVar) in c:\Projects\FSharp.Formatting\src\FSharp.Markdown\MarkdownParser.fs:line 601
  at [email protected](Unit unitVar0)
  at [email protected](Unit unitVar0)
  at Microsoft.FSharp.Collections.Generator.Microsoft-FSharp-Collections-Generator-Generator-1-get_Apply@432.Invoke(Unit unitVar0)
  at Microsoft.FSharp.Collections.Generator.appG[a](Generator`1 g)
  at Microsoft.FSharp.Collections.Generator.EnumeratorWrappingLazyGenerator`1.System-Collections-IEnumerator-MoveNext()
  at Microsoft.FSharp.Collections.SeqModule.ToList[T](IEnumerable`1 source)
  at FSharp.Markdown.Markdown.Parse(String text, String newline) in c:\Projects\FSharp.Formatting\src\FSharp.Markdown\Main.fs:line 56
  at FSharp.Literate.ParseMarkdown.parseMarkdown(String file, String text) in c:\Projects\FSharp.Formatting\src\FSharp.Literate\ParseMarkdown.fs:line 9
  at FSharp.Literate.Literate.ParseMarkdownFile[b](String path, FSharpOption`1 formatAgent, FSharpOption`1 compilerOptions, FSharpOption`1 definedSymbols, FSharpOption`1 references, FSharpOption`1 fsiEvaluator) in c:\Projects\FSharp.Formatting\src\FSharp.Literate\Main.fs:line 85
  

[neoeinstein]

It has been a little while since I was tinkering with this, but regarding #360 and the silent discard of exceptions during evaluation, I think that it is currently explicit here:
https://github.com/tpetricek/FSharp.Formatting/blob/master/src/FSharp.Literate/Evaluator.fs#L170

I would like it if this were changed so that the evaluation would return the error message as output and bind it/result (depending on how the block was defined) to the exception. I could take a swing at, but won't get to it until the weekend at the least.

[dsyme]

Closing this very old issue