Strange behavior of dscom when adding --asmpath containing a backslash in MsBuild Exec task

[carstencodes]

Description

DsCom Build Targets use the directories from the reference assemblies. When MsBuild removes the file names from the items, the trailing backslash remains. This value is passed to dscom.exe tlbexport afterwards. dscom then reports that the directory does not exist. If the trailing backslash removed, the directory is treated as found.

Execution context

The directory path is enclosed by double quotes before the task is executed by msbuild. The command line arguments are passed to dscom.exe via MsBuild Exec task, which itself executes cmd.exe.

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Originally posted by @carstencodes in #440

[matthiasnissen]

Description

DsCom's MSBuild build targets pass directory paths (reference type library paths, assembly search paths, and referenced type library files) to dscom.exe as double-quoted command-line arguments, e.g.:

--asmpath "C:\Some\Directory\" --tlbrefpath "C:\Other\Directory\" --tlbreference "C:\Path\To\Ref.tlb"

When a path ends with a backslash (\) immediately before the closing double quote (\"), the Windows command-line argument parsing convention (used by CommandLineToArgvW and .NET's own argv splitting) treats the backslash as escaping the quote instead of ending the quoted string. As a result, the closing quote is not recognized as a delimiter, and the argument parser merges the current argument with subsequent text on the command line, producing a corrupted/incorrect path.

This causes dscom.exe to report errors such as Directory <corrupted-value> not found., even though the actual target directory exists — simply because it ends with a backslash and is immediately followed by a closing quote.

Execution Context

MSBuild derives directory paths (e.g. from %(RootDir)%(Directory) of resolved references) which naturally retain a trailing backslash after the file name has been stripped. These values are quoted and passed via the Exec task, which invokes cmd.exe, which in turn starts dscom.exe.

Affected Locations

src/dscom.build/dSPACE.Runtime.InteropServices.BuildTasks.Tools.targets:

1. --tlbrefpath (built from DsComTlbExportReferencePaths)
2. --asmpath (built from DsComTlbExportAssemblyPaths / _DsComTlbExportAssemblyPathsWithoutHintPath / WithHintPath)
3. --tlbreference (built from DsComTlbExportTlbReferences)

Reproduction

Running the following via cmd.exe (mimicking MSBuild's Exec task), where both directories actually exist:

"dscom.exe" tlbexport "dummy.dll" --asmpath "C:\repos\dscom\_repro\refs\" --asmpath "C:\repos\dscom\_repro\refs2\" --out "C:\repos\dscom\_repro\out.tlb"

produces:

Failed to export type library. Directory C:\repos\dscom\_repro\refs" --asmpath C:\repos\dscom\_repro\refs2" not found.

The two --asmpath values were merged into a single corrupted argument due to the escaped closing quotes.

Suggested Fix

Before embedding each path into a quoted command-line argument, strip or escape a trailing backslash so it no longer immediately precedes the closing quote. For example, doubling a lone trailing backslash (\" → \\") makes the Windows argv parser emit a single literal backslash and correctly close the quoted argument.