Fix proto build failures being silently ignored in build.sh

[Copilot]

The proto build step (bootstrap compiler tools) could fail without stopping execution, causing the main build to continue with broken dependencies and produce misleading errors downstream.

Root Cause

Line 312 in eng/build.sh had error handling commented out:

"$DOTNET_INSTALL_DIR/dotnet" "${args[@]}"  #$args || exit $?

In bash, # starts a comment, so || exit $? was ignored.

Changes

• Removed #$args comment to enable error handling:

  "$DOTNET_INSTALL_DIR/dotnet" "${args[@]}" || exit $?

• Matches error handling pattern used elsewhere in the script (e.g., line 248 in Test function)

• Allows TrapAndReportError to properly catch and report proto build failures with "Error building tools" message

Impact

Proto build failures now halt execution immediately with clear error messages instead of cascading into confusing main build errors.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>FSharp build shouldn't run when the proto pre-build step fails</issue_title>
<issue_description>Probably due to this line?

fsharp/eng/build.sh

Line 312 in 5e5e0d2

"$DOTNET_INSTALL_DIR/dotnet" "${args[@]}" #$args || exit $?

</issue_description>

Comments on the Issue (you are @copilot in this section)

@ViktorHofer From a GH Copilot chat session:

Yes, you are correct. In the line:

"$DOTNET_INSTALL_DIR/dotnet" "${args[@]}" #$args || exit $?

everything after the # symbol is treated as a comment in shell scripts. That means #$args || exit $? is ignored by the shell and does not affect execution.

Only this part is executed:

"$DOTNET_INSTALL_DIR/dotnet" "${args[@]}"

So, the script will not abort automatically if the command fails, because the error-handling logic (|| exit $?) is commented out. If you want the script to abort on failure, you should remove the #</comment_new>

• Fixes FSharp build shouldn't run when the proto pre-build step fails #19201

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