Treat zero-byte tsconfig.json as an empty config (#4155)

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: jakebailey <5341706+jakebailey@users.noreply.github.com>

Author: Copilot

internal/execute/tsctests/tsc_test.go

@@ -174,6 +174,14 @@ func TestTscCommandline(t *testing.T) {
 			},
 			commandLineArgs: []string{"-p", "/home/src/workspaces/project"},
 		},
+		{
+			subScenario: "Parse -p with empty tsconfig file",
+			files: FileMap{
+				"/home/src/workspaces/project/first.ts":      `export const a = 1`,
+				"/home/src/workspaces/project/tsconfig.json": ``,
+			},
+			commandLineArgs: []string{"-p", "."},
+		},
 		{
 			subScenario:     "Parse enum type options",
 			commandLineArgs: []string{"--moduleResolution", "nodenext ", "first.ts", "--module", "nodenext", "--target", "esnext", "--moduleDetection", "auto", "--jsx", "react", "--newLine", "crlf"},

internal/tsoptions/commandlineparser.go

@@ -217,7 +217,7 @@ func tryReadFile(fileName string, readFile func(string) (string, bool), errors [
 	// this function adds a compiler diagnostic if the file cannot be read
 	text, e := readFile(fileName)
 
-	if !e || text == "" {
+	if !e {
 		// !!! Divergence: the returned error will not give a useful message
 		// errors = append(errors, ast.NewCompilerDiagnostic(diagnostics.Cannot_read_file_0_Colon_1, *e));
 		text = ""

testdata/baselines/reference/tsc/commandLine/Parse--p-with-empty-tsconfig-file.js

@@ -0,0 +1,38 @@
+currentDirectory::/home/src/workspaces/project
+useCaseSensitiveFileNames::true
+Input::
+//// [/home/src/workspaces/project/first.ts] *new* 
+export const a = 1
+//// [/home/src/workspaces/project/tsconfig.json] *new* 
+
+
+tsgo -p .
+ExitStatus:: Success
+Output::
+//// [/home/src/tslibs/TS/Lib/lib.es2025.full.d.ts] *Lib*
+/// <reference no-default-lib="true"/>
+interface Boolean {}
+interface Function {}
+interface CallableFunction {}
+interface NewableFunction {}
+interface IArguments {}
+interface Number { toExponential: any; }
+interface Object {}
+interface RegExp {}
+interface String { charAt: any; }
+interface Array<T> { length: number; [n: number]: T; }
+interface ReadonlyArray<T> {}
+interface SymbolConstructor {
+    (desc?: string | number): symbol;
+    for(name: string): symbol;
+    readonly toStringTag: symbol;
+}
+declare var Symbol: SymbolConstructor;
+interface Symbol {
+    readonly [Symbol.toStringTag]: string;
+}
+declare const console: { log(msg: any): void; };
+//// [/home/src/workspaces/project/first.js] *new* 
+export const a = 1;
+
+