refactor(csv): remove dead code and improve tests (#5151)

csv/parse.ts

@@ -50,35 +50,29 @@ class Parser {
   #readLine(): string | null {
     if (this.#isEOF()) return null;
 
-    if (
+    let buffer = "";
-      !this.#input.startsWith("\r\n", this.#cursor) ||
+    let hadNewline = false;
-      !this.#input.startsWith("\n", this.#cursor)
+    while (this.#cursor < this.#input.length) {
-    ) {
+      if (this.#input.startsWith("\r\n", this.#cursor)) {
-      let buffer = "";
+        hadNewline = true;
-      let hadNewline = false;
+        this.#cursor += 2;
-      while (this.#cursor < this.#input.length) {
+        break;
-        if (this.#input.startsWith("\r\n", this.#cursor)) {
+      }
-          hadNewline = true;
+      if (
-          this.#cursor += 2;
+        this.#input.startsWith("\n", this.#cursor)
-          break;
+      ) {
-        }
+        hadNewline = true;
-        if (
-          this.#input.startsWith("\n", this.#cursor)
-        ) {
-          hadNewline = true;
-          this.#cursor += 1;
-          break;
-        }
-        buffer += this.#input[this.#cursor];
         this.#cursor += 1;
+        break;
       }
-      if (!hadNewline && buffer.endsWith("\r")) {
+      buffer += this.#input[this.#cursor];
-        buffer = buffer.slice(0, -1);
+      this.#cursor += 1;
-      }
-
-      return buffer;
     }
-    return null;
+    if (!hadNewline && buffer.endsWith("\r")) {
+      buffer = buffer.slice(0, -1);
+    }
+
+    return buffer;
   }
   #isEOF(): boolean {
     return this.#cursor >= this.#input.length;

csv/parse_test.ts

@@ -813,6 +813,24 @@ Deno.test({
         assertEquals(parse(input, { trimLeadingSpace: true }), output);
       },
     });
+    await t.step({
+      name: "leading line breaks",
+      fn() {
+        const input = "\n\na,b,c";
+        const output = [["a", "b", "c"]];
+        assertEquals(parse(input), output);
+      },
+    });
+    await t.step({
+      name: "throws when skipFirstRow=true with empty data",
+      fn() {
+        assertThrows(
+          () => parse("", { skipFirstRow: true }),
+          Error,
+          "Headers must be defined",
+        );
+      },
+    });
   },
 });