MSBuild Task: error if no assembly references in .cobraproj file

[thriwkin]

On Windows, using "msbuild.exe" with a file "X.cobraproj" without any assembly references, for example

<Reference Include="System" /> 

causes this error message:

...Cobra.targets(149,3): error MSB6001: 
    Invalid command line switch for "cobra.bat". 
    Value cannot be null. [...X.cobraproj]
...Cobra.targets(149,3): error MSB6001: 
    Parameter name: collection [...X.cobraproj]

Steps to reproduce the failure:
call

msbuild X.cobraproj

where "X.cobraproj" is this file

<Project xmlns="http://schemas.microsoft.com/developer/msbuild/2003"
  ToolsVersion="4.0" DefaultTargets="Build" >
  <PropertyGroup>
    <OutputPath></OutputPath>
    <AssemblyName>Hello</AssemblyName>
    <OutputType>Exe</OutputType>
  </PropertyGroup>
  <ItemGroup>
    <Compile Include="Hello.cobra" />
  </ItemGroup>
  <Import Project="$(MSBuildExtensionsPath)/Cobra/Cobra.targets" />
</Project>

and "Hello.cobra" is this file:

class Program
    def main is shared
        print "Hello!"

Note:
The above "X.cobraproj" works with "xbuild.exe".
With "msbuild.exe" it only works with an assembly reference, for example:

  ...
  <ItemGroup>
    <Compile Include="Hello.cobra" />
    <Reference Include="System" />
  </ItemGroup>
  ...

[thriwkin]

The failure is caused by (a typo?) in file "CobraCompiler.cobra":

class CobraCompiler ...
    def generateCommandLineCommands as String ...
        ...
        refs = List<of ITaskItem>(.references)
        ...

A simple fix:

class CobraCompiler ...
    def generateCommandLineCommands as String ...
        ...
        if .references
            refs = List<of ITaskItem>(.references)
            ...

Note: This changeset does not fix the error:
http://cobra-language.com/trac/cobra/changeset/3061

Question:
To which "Component" belongs the Cobra MSBuild Task (Cobra.MSBuild.dll)?
The dropdown box "Component:" offers these options only:
- Cobra Compiler
- Cobra IDE: Miscellaneous
- Cobra Web Site: ...

[nerdzero]

Looks like a reasonable fix. Did you try it?

Just curious, how are you building these project files? By hand or by modifying the configuration parameters via the GUI screen in MonoDevelop?

[thriwkin]

Looks like a reasonable fix. Did you try it?

Yes, see below.

how are you building these project files?

With an editor (SciTE), on Windows,
because this X.cobraproj file is suitable for tests
- on Windows, .NET, msbuild.exe, and
- on Windows, Mono, xbuild.exe,
and it is as simple as possible (reduces the number of possible causes of a failure).

History
When I tried out the MD/XS addin (v0.5.1, end of last year)
I always encountered this failure, as described above.
When I looked into the source code of the MSBuild task (in CobraCompiler.cobra),
I found that it is caused by this statement

refs = List<of ITaskItem>(.references)

Then (end of last year) changeset:3061 appeared: instead of changing the source of the MSBuild Task, it changes 5 test/demo project files. To each file it adds an assembly reference (System.Core)
- which prevents the failure -- it causes that the Task parameter .references will not be nil,
- but which is not needed -- the Task has to remove it, because it cannot prevent that the Cobra compiler does implicitly add this reference.

So I wondered:
"Why do they not fix the bug by inserting an if .references, ... into the source of the Task?"

Later I got this idea: "Maybe it is an issue on .NET only, but not on Mono."
To test this, I made this simple X.cobraproj file.
With both, .NET and Mono installed on Windows, I can test:
- msbuild.exe X.cobraproj
- xbuild.bat X.cobraproj
(the xbuild.bat calls ...\mono.exe" %MONO_OPTIONS% ...\xbuild.exe" %*)

Results of the tests
1. If the .cobraproj file does not contain any assembly references
- on Mono with xbuild, the Task will be called with .references <> nil and .references.count == 0
- on .NET with msbuild, the Task will be called with .references == nil,
-- which causes that the statement refs = List<of ITaskItem>(.references) throws an Exception.

2. If the Task is modified as described above,
then the X.cobraproj runs
- with or without any assembly references, on both,
- on .NET with msbuild, and
- on Mono with xbuild,
where X.cobraproj is:

<Project xmlns="http://schemas.microsoft.com/developer/msbuild/2003"
  ToolsVersion="4.0" DefaultTargets="Rebuild" >
  <PropertyGroup>
    <OutputPath>bin</OutputPath>
    <AssemblyName>Hello</AssemblyName>
    <OutputType>Exe</OutputType>
  </PropertyGroup>
  <ItemGroup>
    <Compile Include="Hello.cobra" />
<!-- 
    <Reference Include="System" /> 
-->
 </ItemGroup>
  <Import Project="$(MSBuildExtensionsPath)/Cobra/Cobra.targets" />
</Project>

3. I also tested the modified Task with the MD/XS addin (v0.5.1, end of last year):
- on Windows, .NET, msbuild.exe: it worked with or without assembly references.

[thriwkin]

Correction:

Results of the tests (1.)

Correct is:
If the X.cobraproj file does not contain any assembly references
then

• on Windows, .NET, msbuild: the Task will be called with .references == nil
  -- which causes that the statement refs = List<of ITaskItem>(.references) throws an Exception.
• on Windows, Mono, xbuild, ToolsVersion="4.0": the Task will be called with .references <> nil and .references.length == 1 and .references[0].itemSpec: "...System.Core".