feat(cli): respect TypeScript suppression directives for import diagnostics

[ddevilz]

feat(cli): respect TypeScript suppression directives for import diagnostics

Fixes #32822

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What

Respect TypeScript suppression directives (@ts-ignore and @ts-expect-error) for import-related diagnostics in the CLI type checker.

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Why

Previously, Deno's type checker ignored suppression comments for unresolved import errors, making it impossible to suppress known or intentional "module not found" diagnostics.

This behavior was inconsistent with developer expectations when using TypeScript suppression directives.

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How

• Added check_suppressed_at() helper function to centralize suppression checking logic
• Updated is_resolution_suppressed() to use AST-based detection for accurate positioning
• Added parsed source caching to avoid re-parsing the same files multiple times
• Updated GraphWalker to check for suppression before pushing to missing_diagnostics
• Handles both single-line (//) and block (/* */) comment formats
• Supports multi-line imports by finding the AST declaration that spans the error position

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Behavior

Before

// @ts-ignore
import x from "non-existent-module";
// ❌ Error: module not found

After

// @ts-ignore
import x from "non-existent-module";
// ✅ No diagnostic emitted

Also supports multi-line imports:

// @ts-ignore
import {
  foo,
  bar,
} from "non-existent-module";
// ✅ No diagnostic emitted

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Features

• Single-line comments: // @ts-ignore and // @ts-expect-error
• Block comments: /* @ts-ignore */ and /* @ts-expect-error */
• Multi-line imports: Correctly handles imports spanning multiple lines
• Performance: Caches parsed sources to avoid redundant parsing
• Precision: Uses AST analysis to accurately position suppression comments
• Flexible formatting: Handles various whitespace patterns and annotation messages

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Design Notes

• Uses get_leading() to avoid false positives from inline comments on preceding statements
• AST-based approach ensures accurate handling of complex import structures
• Caching mechanism improves performance for large codebases
• Modular design with extracted helper functions improves maintainability

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Testing

• Comprehensive test suite covering all suppression scenarios

• Tests include:

  • Single-line and block comment suppression
  • Multi-line import handling
  • Whitespace variations and annotation messages
  • Edge cases (blank lines, inline comments, non-suppression cases)

• All tests pass in x test-spec ts_ignore_import

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Implementation Details

• Files modified: cli/type_checker.rs, cli/factory.rs
• Performance: Added parsed_source_cache to GraphWalker for efficient parsing
• Modularity: Extracted check_suppressed_at() helper function to reduce code duplication
• Accuracy: AST-based detection handles complex import structures correctly

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Checklist

• ./x fmt passes
• ./x lint passes
• ./x test-spec ts_ignore_import passes
• Issue linked (unresolved import errors can't be suppressed with // @ts-expect-error or // @ts-ignore comment #32822)

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AI Disclosure

I used AI assistance to help with implementation, test writing, and drafting this PR description.