[mono] Fix crash in AssemblyBuilder::GetModules

[uweigand]

• The "modules" field may be null if called before the end of the
  AssemblyBuilder ctor (which may happen in an OnAssemblyLoad event
  handler invoked during the basic_init VM call).

This happens during some aspnetcore test cases. I'm not completely sure if the OnAssemblyLoad event handler is supposed to see that singleton module or not (looking at the CoreCLR sources I believe it may there), but that seems difficult to implement in Mono due to interactions between the basic_init calls in AssemblyBuilder vs. ModuleBuilder.

In any case, this patch at least removes the crash by special-casing a null modules fields (like several other AssemblyBuilder accessor functions already do!), and the aspnetcore tests now pass.

[dotnet-issue-labeler]

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[lambdageek]

May be related to the null GetModules that we saw in dotnet/aspnetcore#33152 (comment) that I wasn't able to reproduce with a straightforward test.

[uweigand]

May be related to the null GetModules that we saw in dotnet/aspnetcore#33152 (comment) that I wasn't able to reproduce with a straightforward test.

Yes, this is exactly the code path in aspnetcore where I saw the crash. (I'm still using the preview5 level of aspnetcore which doesn't have dotnet/aspnetcore#33263 applied yet.)

[ghost]

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Issue Details

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• The "modules" field may be null if called before the end of the
  AssemblyBuilder ctor (which may happen in an OnAssemblyLoad event
  handler invoked during the basic_init VM call).

This happens during some aspnetcore test cases. I'm not completely sure if the OnAssemblyLoad event handler is supposed to see that singleton module or not (looking at the CoreCLR sources I believe it may there), but that seems difficult to implement in Mono due to interactions between the basic_init calls in AssemblyBuilder vs. ModuleBuilder.

In any case, this patch at least removes the crash by special-casing a null modules fields (like several other AssemblyBuilder accessor functions already do!), and the aspnetcore tests now pass.

Author:	uweigand
Assignees:	-
Labels:	area-System.Reflection-mono
Milestone:	-

[ghost]

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