[SAOC 2025] Separate Semantic Routines from AST Nodes Weekly Update #3

[Mohamed El Shorbagy]

## Summary of Progress (September 29 - October 06)
This week, I further eliminated some semantic function calls 
inside AST node files, and I am still working on some of the 
previous issues I encountered during this process.

## What I Worked On

1. Moved `ClassReferenceExp.getFieldIndex` and 
`StructLiteralExp.getFieldIndex` to `dmd/expressionsem.d` to 
eliminate calls to `Type.size` (See [Merged 
PR](https://github.com/dlang/dmd/pull/21931)).

2. Broke semantic dependency of `dmd/expression.d` on 
`dmd/typesem.d` by moving `Expression.isLvalue` to 
`dmd/expressionsem.d` to eliminate calls to `typesem.mutableOf` 
and `typesem.unSharedOf` (See [Merged 
PR](https://github.com/dlang/dmd/pull/21935)).

3. (WIP) Still figuring out the proper places to call 
`oneMembers` and `computeIsTrivialAlias` (See 
[PR](https://github.com/dlang/dmd/pull/21917/files)).

4. (WIP) Fixing the problem of casting 
`TemplateDeclaration.instances` from `void *` to 
`TemplateInstance[TemplateInstanceBox]` to break semantic 
dependency of `dtemplate.d` on `templatesem.d`. There is an 
issue, however, with an old bootstrap compiler (v2.079) when 
doing the following:
```d
auto instances = new TemplateInstance[TemplateInstanceBox];
```
The error message is (as far as I remember): can only `new` 
structs, classes and dynamic arrays, not 
`TemplateInstance[TemplateInstanceBox]`.
Therefore, we did a workaround by using `root.aav.AssocArray`; 
however, this implementation does not support `.remove` or 
`.clear` operations that are needed by various functions in 
`templatesem.d` and `traits.d` (See 
[PR](https://github.com/dlang/dmd/pull/21937)).