[Hrushikesh Ramilla (Hrushikesh-ramilla)]

Fixes #3614

Problem

In createVirtualTypeScriptEnvironment, createFile and updateFile currently parse a full s.SourceFile AST and pass it to the compiler host (updateFile), which stores it in its internal sourceFiles map.
However, the language service never reads that map — its host's getScriptSnapshot reads raw text from sys, and the language service parses and caches its own SourceFile ASTs from those snapshots.
As a result, every file in the virtual TypeScript environment is held in memory as two duplicate ASTs.

Solution

• In createVirtualTypeScriptEnvironment, pass { fileName, text } instead of parsing an unread duplicate s.createSourceFile() or s.updateSourceFile().
• In createVirtualLanguageServiceHost, write directly to sys and avoid storing redundant SourceFiles in the compiler host map.
• Added comprehensive unit tests in packages/typescript-vfs/test/index.test.ts verifying that s.createSourceFile and s.updateSourceFile are not parsed redundantly and that language service AST retrieval works on demand.

Verification

pm test in packages/typescript-vfs: 25 / 25 tests passed (including new tests).

• dts lint: 0 errors.

[Hrushikesh Ramilla (Hrushikesh-ramilla)]

@microsoft-github-policy-service agree