dotnet/msbuild

Error MSB4012 could be more helpful

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#656 opened on May 26, 2016

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Area: Debuggabilityhelp wantedtriaged

Description

In the spirit of https://twitter.com/GregorySchier/status/732830868562182144, this could be improved:

error MSB4012: The expression "o:\msbuild\bin\Debug-NetCore\Windows_NT_Deployment\\@(ResolvedRuntimeFiles->'%(DestinationSubDirectory)')" cannot be used in this context. Item lists cannot be concatenated with other strings where an item list is expected. Use a semicolon to separate multiple item lists.

"Use a semicolon" is a good suggestion (and should probably be the only one if there's no item transform involved), but there's another common case where you can run into this: when the solution is to move the initial string inside the item transform. We could suggest that rewriting as well:

error MSB4012: The expression "{0}" cannot be used in this context. Item lists cannot be concatenated with other strings where an item list is expected. Use a semicolon to separate multiple item lists, or move {1} inside the item transformation to prefix every transformation output with the string.

Contributor guide

Tech stack
csharp
Domain
developer experiencebuild system
Issue type
feature
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
2
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
basic C# knowledgefamiliarity with MSBuild
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
75
Research direction
The goal is to improve the error message for MSB4012. The current error suggests using a semicolon, but there is another common case where the solution is to move the initial string inside the item transform. The fix requires modifying the error message string in the MSBuild source code, likely in a file that handles error formatting. Locate the source file containing the MSB4012 error message (e.g., in the Shared or Engine directory). Update the error message to include an additional suggestion: 'or move {1} inside the item transformation to prefix every transformation output with the string.' Ensure the new message is consistent with the existing style and test that it builds correctly. No linked PRs or comments provide further direction.