Compile to IEC 61131-10 XML - Omron

[DoubleCouponDay]

Based on my discussion post here, I've implemented XML generation as a first class compilation target. For now, the implementation focuses on complying with the specific subset of Structured Text compatible with Sysmac Studio. All that is required is to add the --xml-omron argument to a compilation command. the new plc_xmlgen module should be portable enough to handle other specific subsets in the future, such as CODESYS.

Here is an example of usage:

plc ./source/clampandsaw.st ./source/testallbuiltins.st --xml-omron -i ./externals/stdlib_externals.st -i ./externals/omron_externals.st -l iec61131std -l libNX1P2 -l ws2_32 -l ntdll -l userenv -o ./compiled/lib_structured_text.xml

For this to work, the builtins of a specific PLC device are compiled into a separate library which can be linked to. As a result, VAR_EXTERNAL and VAR_EXTERNAL CONSTANT had to be implemented. Without external references to a stub library, none of the references to built in constants, types, and global functions could compile.

To be clear, Sysmac does not support the following ST syntax:

• no POINTER TO
• no REFERENCE TO
• no WSTRING
• no CLASS
• no INTERFACE
• no ALIAS TO
• no WSTRING

Unit tests have been added to confirm the feature.

Here is a concise list of changes made in this PR:

New XML export target

• Added compiler/plc_xmlgen crate: xml_gen.rs generator plus a serializer.rs typed node builder for IEC 61131-10 Ed1 XML.
• Added --xml-omron CLI flag and a GenerationParameters struct threaded from CompileParameters through CompileOptions into codegen.
• Added FormatOption::XML with .xml output naming in plc_project and the codegen participant.
• Added GeneratedModule::persist_to_xml, wired into persist alongside the object/IR/bitcode arms.
• Added copy_xmlfile_to_output as the XML link step in GeneratedProject.
• PipelineParticipant::generate now receives &AnnotatedProject and &CompileOptions so the generator can see the AST, not just the LLVM module.
• Validates generated XML against the bundled Omron schema before writing.

Type rendering for Sysmac

• Emits only StructTypeSpec and EnumTypeWithNamedValueSpec declarations, the two Sysmac actually accepts.
• Resolves aliases, arrays and strings to inline TypeName text at every use site instead of declaring them.
• Renders arrays as ARRAY[0..3] OF X, multi-dimensional as ARRAY[0..1,1..3] OF X with no space after the separator.
• Renders strings as String[n], defaulting to String[80] to match DEFAULT_STRING_LEN.
• Recursively resolves nested element types through alias chains, with a hop limit guarding self-referential aliases.

New diagnostic

• Added E152 (error) for constructs the chosen XML target cannot represent, with a markdown doc page.
• plc_xmlgen scans user types, globals, POU variable blocks and struct members, skipping external linkage and compiler-generated declarations.

VAR_EXTERNAL behaviour

• Removed the E106 "VAR_EXTERNAL blocks have no effect" warning and its diagnostic entry, doc file and tests.
• The initializer lowering now skips external blocks and no longer emits external constructor bodies for standalone declarations.
• get_struct_member_index now allows external variables as member index.
• Vtable generation forces internal linkage when constructors are generated internally.

Supporting changes

• Added Display impls for AstLiteral, Array, Date, Time, TimeOfDay and DateAndTime so literals can be serialised as text.
• Made SourceLocation.span/file and TextLocation.line/column/offset public.
• Lowercased VariableBlockType's Display output to match the XML attribute vocabulary.
• Fixed Windows MSVC linking in the stdlib integration test harness (/MD, explicit exports and system libs).
• Documented the new target in book/src/using_rusty.md.

[codecov]

Codecov Report

❌ Patch coverage is 80.92536% with 437 lines in your changes missing coverage. Please review.
✅ Project coverage is 92.88%. Comparing base (1e70538) to head (9c2990b).
⚠️ Report is 220 commits behind head on master.

Files with missing lines	Patch %	Lines
compiler/plc_xmlgen/src/serializer.rs	24.30%	218 Missing ⚠️
compiler/plc_xmlgen/src/xml_gen.rs	83.28%	120 Missing ⚠️
compiler/plc_ast/src/literals.rs	9.75%	37 Missing ⚠️
src/codegen.rs	6.45%	29 Missing ⚠️
libs/stdlib/tests/common/mod.rs	0.00%	13 Missing ⚠️
compiler/plc_driver/src/pipelines.rs	65.38%	9 Missing ⚠️
compiler/plc_driver/src/pipelines/participant.rs	58.82%	7 Missing ⚠️
compiler/plc_ast/src/ast.rs	93.75%	1 Missing ⚠️
compiler/plc_driver/src/cli.rs	80.00%	1 Missing ⚠️
compiler/plc_project/src/project.rs	0.00%	1 Missing ⚠️
... and 1 more

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1896      +/-   ##
==========================================
- Coverage   94.68%   92.88%   -1.80%     
==========================================
  Files         188      197       +9     
  Lines       58726    78862   +20136     
==========================================
+ Hits        55603    73252   +17649     
- Misses       3123     5610    +2487     

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