S7 Lint for VS Code

S7 Lint for VS Code is an extension for static analysis and editor support for Siemens TIA Portal source and export formats.

This is an independent open-source project. It is not an official Siemens product and is not affiliated with, endorsed by, sponsored by, or maintained by Siemens AG. Siemens, SIMATIC, TIA Portal, and other product names are trademarks of their respective owners.

The extension is currently version 0.1.6 and under active development. It is intended to catch common structural, type, symbol, and instruction-call errors before code is imported or compiled in TIA Portal. It is not a replacement for the target CPU and TIA Portal compiler.

Supported files

• .scl: authored SCL files containing one or more block or type declarations.
• .s7dcl: LAD/FBD declaration exports, program blocks, and TYPE declarations.
• .udt: text-format PLC data type declarations.
• **/*.xml: TIA XML exports, anywhere in the workspace. PLC data type exports feed the workspace type cache; DATA_BLOCK exports (SW.Blocks.InstanceDB/ GlobalDB) feed the block index, so references to an instance DB resolve even though TIA writes it in a different format from the FUNCTION_BLOCK it instances. Every file is offered to both parsers -- they key off different root elements -- because export layout does not reliably separate the two.
• .s7res: multilingual resources with YAML/schema/duplicate-ID validation, MLC cross-reference diagnostics, definition, rename, and inline-hint support.

Current capabilities

Diagnostics

• SCL source: Checks syntax structure, symbols, member access, conditions, expressions, conversions, loops, literals, and instruction-result usage.
• Instruction calls: Validates LAD/FBD and SCL names, pins, parameters, call shapes, templates, result use, language support, and selected memory rules against the registries under resources/.
• Graphical networks: Checks LAD/FBD rung connectivity back to wire#powerrail.
• Workspace symbols and types: Resolves PLC tags from XML exports in .scl and .s7dcl, and checks UDT dependencies, duplicate declarations, circular references, array bounds, and nesting limits.
• Declarations and data access: Applies section, reference, pointer, array, operand-type, and selected cross-parameter rules when enough context exists.
• Multilingual resources: Validates .s7res structure, IDs, text values, MLC references, and orphaned entries before TIA Portal import.

Bare local names without # and differently cased type names are recognized the same way as by TIA Portal's external-source importer and receive the same validation as their canonical forms.

The parser and checks are deliberately conservative: when a type, target, or expression cannot be resolved confidently, the extension avoids guessing.

Editor support

• Completion: Context-aware suggestions for declarations, data types, instructions, symbols, and block templates. Chained member completion works across local tags, UDTs, inline structures, system types, FUNCTION_BLOCKs, DATA_BLOCKs, and instruction instances.
• Navigation and refactoring: Hover, definition, and rename support for local and workspace symbols, including bare SCL names, UDTs, blocks, and instance DATA_BLOCKs.
• Semantic highlighting: Distinguishes elementary and project data types, callable types and instances, DATA_BLOCKs, PLC tags, interface members, containers, indexable values, operators, constants, and control-flow keywords. It follows the active VS Code theme, with an optional managed S7 color preset.
• Storage layout: Hover shows calculated size, padding, byte offsets, and packed BOOL bit positions for resolvable UDT, DATA_BLOCK, array, string, and nested-structure layouts.
• Quick fixes: Adds explicit conversions, generates local or single-instance DATA_BLOCKs, creates or repairs sibling .s7res files and MLC entries, and fixes supported instruction-registry gaps.
• Multilingual resources: Definition, rename, and inline text hints for .s7res, with configurable locale fallback.
• Instruction Registry Editor: A visual editor for instruction and system- type YAML with validation, drag-and-drop ordering, undo/redo, and automatic rule reload and re-lint after saving.

Knowledge bases

The YAML under resources/ is hand-maintained source data and is loaded directly at runtime:

• instruction-registry/: LAD/FBD and SCL instruction signatures.
• type-registry/: base types, system types, expression domains, composition rules, and declaration constraints.
• diagnostic-registry/: diagnostic codes, severities, and message templates.
• system-registry/: shared memory-area and instruction-result schemas.

There is no generated mirror or synchronization step for these registries.

Repository layout

./
  src/                         extension, parsers, analysis, providers, linters
  resources/                   runtime YAML registries
  docs/fbd-knowhow/            LAD/FBD syntax and fixture-derived notes
  docs/source-document-format/ independent source-format interoperability notes
  scripts/                     test runners and fixtures (source repository only)
  syntaxes/                    VS Code language grammar and configuration
  themes/                      bundled VS Code theme

Build and test

The published VSIX excludes scripts/**. Test commands are development workflows and must be run from a source checkout. All test runners and fixtures are available in the GitHub repository under scripts/.

Run commands from the repository root:

npm install
npm test

npm test compiles the extension and runs all regression suites. The focused commands below link to their test runners in the GitHub repository:

The optional npm run test:highlight command uses test-semantic-highlighting.js from the same GitHub directory.

The diagnostic fixtures and their assertion contracts are documented in scripts/fixtures/scl-diagnostics/.

Press F5 in VS Code with this directory open to launch an Extension Development Host. The launch configuration compiles and bundles the extension first.

Package a VSIX

npm run bundle
npx @vscode/vsce package

Commands and settings

The extension contributes these commands:

• S7 Lint: Rebuild Type Cache
• S7 Lint: Re-lint All Open Files
• S7 Lint: Show Loaded Rule Stats
• S7 Lint: Open Instruction Registry Editor
• S7 Lint: Install Recommended Semantic Colors
• S7 Lint: Disable Recommended Semantic Colors

Two further commands back the registry quick fixes (tiaLint.registryMarkPinOptional, tiaLint.registryScaffoldInstruction). They take arguments supplied by the diagnostic, so they are hidden from the command palette and are invoked from the lightbulb only.

tiaLint.mlcLocale selects the preferred locale for multilingual resource resolution. Resolution falls back to en-US and then to an available locale.

tiaLint.recommendedSemanticColors.enabled controls automatic installation of the theme-scoped S7 semantic palette. Disabling it removes only values managed by S7 Lint and preserves unrelated or manually customized semantic colors.

Known limitations

• Target-specific validation: CPU family, firmware, and a block's IEC-check setting are not available from the supported project sources. Platform data in platform-availability.NOTLOADED.yaml is therefore not loaded. When IEC modes permit different results, the linter uses the permissive interpretation; bit-string arithmetic is one example.
• FUNCTION result types: The result variable is recognized, but its declared return type is not retained by the parser. Assignments to it are therefore not type-checked.
• Incomplete type information: Checks that require an unresolved symbol or an expression without one safely inferred type are skipped instead of guessed.
• Operator spacing: The lexer treats + or - immediately followed by a digit as part of a signed number. Consequently, 4-1 loses its subtraction operator and can produce a missing-semicolon diagnostic; use 4 - 1.
• XML source locations: XML UDT members do not retain source positions, so related cache diagnostics point to line 1 instead of the exact member.
• Workspace updates: Relevant file changes rebuild the complete type and block caches rather than updating only the affected entries.
• Registry confidence: Checks based on shape-only instruction entries are generally warnings. Hard errors require stronger evidence such as confirmed-compiled data.

Source-format scope and attribution are documented separately in docs/source-document-format/.

License

Licensed under the Apache License 2.0.