[RFC0017] Add invalid and missingerror values

[jrentlez]

Depends on #674.

This PR implements RFC0017, accepted in #670.

Also included is a restructuring of PostgresLoaderExecutor with a more granular try/catch.

Reason for the draft status: The RFC states that a log message must be emitted every time an error is assigned to a variable. I still need to make sure that is actually the case in the implementation

Edit: sorry for the large diff

[Copilot]

Pull Request Overview

This PR implements RFC0017 by introducing invalid and missing error values to represent failed evaluations instead of returning undefined. The implementation adds new error classes (InvalidError and MissingError) and replaces undefined returns throughout the codebase with these error objects. Additionally, it includes a restructuring of PostgresLoaderExecutor with more granular error handling.

• Introduces new error types InvalidError and MissingError with corresponding type guards
• Replaces undefined returns with error objects throughout expression evaluation and property handling
• Updates all value type classes to handle error representations in type checking methods
• Restructures PostgresLoaderExecutor with granular try/catch blocks for better error isolation

Reviewed Changes

Copilot reviewed 55 out of 55 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
libs/language-server/src/lib/ast/expressions/internal-value-representation.ts	Defines new error classes and updates internal value representation types
libs/language-server/src/lib/ast/expressions/typeguards.ts	Adds type guards for error detection and removes unused helper function
libs/language-server/src/lib/ast/expressions/evaluate-expression.ts	Updates expression evaluation to return errors instead of undefined
libs/language-server/src/lib/ast/wrappers/value-type/value-type.ts	Updates ValueType interface to handle error representations
libs/language-server/src/lib/validation/validation-util.ts	Replaces undefined check with error type guard
libs/extensions/rdbms/exec/src/lib/postgres-loader-executor.ts	Restructures with granular error handling methods

Comments suppressed due to low confidence (2)

libs/language-server/src/lib/ast/expressions/typeguards.ts:69

• [nitpick] The function name ERROR_TYPEGUARD is inconsistent with the pattern of other type guards. Consider renaming to ERROR_TYPEGUARD or isError for better consistency with other type guard naming conventions.

export const ERROR_TYPEGUARD = (

libs/extensions/rdbms/exec/src/lib/postgres-loader-executor.ts:61

• The method name createError is ambiguous. Consider renaming to createExecutionError or formatDatabaseError to better indicate it creates a Result with error information, not just an Error object.

  private createError(

[georg-schwarz]

Very nice progress! Left some comments to discuss and/or address ;-)

[georg-schwarz]

Phew, what a great addition! Left some minor comments you can address if you want. Aside from that, ready to merge from my side!