Fix inferred project JavaScript file support when compiler options are provided

[Copilot]

Fourslash tests failed for .js files when compiler options were provided to the inferred project without explicitly setting AllowJs. The inferred project only applied its AllowJs: true default when compilerOptions == nil, causing .js files to be excluded from the project.

Changes

Fix in internal/project/project.go:

func NewInferredProject(...) {
    if compilerOptions == nil {
        compilerOptions = &core.CompilerOptions{
            AllowJs: core.TSTrue,
            // ... other defaults
        }
    } else {
        // Apply defaults for unset options
        if compilerOptions.AllowJs == core.TSUnknown {
            compilerOptions.AllowJs = core.TSTrue
        }
    }
    // ...
}

Now applies AllowJs: true default when the option is unset (TSUnknown), regardless of whether compilerOptions is nil.

Test coverage in internal/fourslash/tests/test_js_file_issue_test.go:

• .js files with no JS-related compiler options (reproduces bug, verifies fix)
• .js files with @checkJs: true (ensures existing behavior preserved)
• .js files with explicit @allowJs: false (ensures explicit settings override defaults)

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Fourslash is broken when making requests in unconfigured .js files</issue_title>
<issue_description>Error message:

--- FAIL: TestAutoImportCompletionJs (0.07s)
    c:/typescript-go/internal/fourslash/tests/autoImportCompletion_test.go:159: At marker 'd': textDocument/completion request returned error: [-32603]: no project found for URI file:///d.js
FAIL
FAIL	github.com/microsoft/typescript-go/internal/fourslash/tests	1.758s

Repro:

Fails on requests called in .js files (formatting, completions, codefixes, etc)

Example: in internal/fourslash/tests/autoImportCompletions_test.go:

func TestAutoImportCompletionJs(t *testing.T) {
	t.Parallel()
	defer testutil.RecoverAndFail(t, "Panic on fourslash test")
	const content = `// @Filename: a.js
export const someVar = 10;

// @Filename: d.js
import {someVar} from "./a";
someVar;
a/*d*/
`
	f, done := fourslash.NewFourslash(t, nil /*capabilities*/, content)
	defer done()
		f.VerifyCompletions(t, "d", &fourslash.CompletionsExpectedList{
		UserPreferences: &lsutil.UserPreferences{
			IncludeCompletionsForModuleExports:    core.TSTrue,
			IncludeCompletionsForImportStatements: core.TSTrue,
		},
		IsIncomplete: false,
		ItemDefaults: &fourslash.CompletionsExpectedItemDefaults{
			CommitCharacters: &DefaultCommitCharacters,
			EditRange:        Ignored,
		},
		Items: &fourslash.CompletionsExpectedItems{
			Includes: []fourslash.CompletionsExpectedItem{"someVar", "anotherVar"},
		},
	})
}

Info:

I've traced it back to .js files not being found in a project during GetDefaultProject</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Fourslash is broken when making requests in unconfigured .js files #2621

---

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[jakebailey]

This seems vaguely right given InferredProject has:

    override setCompilerOptions(options?: CompilerOptions): void {
        // Avoid manipulating the given options directly
        if (!options && !this.getCompilationSettings()) {
            return;
        }
        const newOptions = cloneCompilerOptions(options || this.getCompilationSettings());
        if (this._isJsInferredProject && typeof newOptions.maxNodeModuleJsDepth !== "number") {
            newOptions.maxNodeModuleJsDepth = 2;
        }
        else if (!this._isJsInferredProject) {
            newOptions.maxNodeModuleJsDepth = undefined;
        }
        newOptions.allowJs = true;
        super.setCompilerOptions(newOptions);
    }

But, mutating the input seems suspect