fix sed-lite implementation

.pre-commit-config.yaml

@@ -2,7 +2,7 @@
 # See https://pre-commit.com/hooks.html for more hooks
 repos:
   - repo: https://github.com/pre-commit/pre-commit-hooks
-    rev: v3.2.0
+    rev: v6.0.0
     hooks:
       - id: trailing-whitespace
       - id: end-of-file-fixer

sed-lite/src/main.zig

@@ -9,7 +9,7 @@ pub fn main() !u8 {
     var stdout_writer = std.fs.File.stdout().writer(&stdout_buffer);
     var stderr_writer = std.fs.File.stdout().writer(&.{});
     const stdout = &stdout_writer.interface;
-    defer stdout.flush() catch {};
+    defer stdout.flush() catch @panic("flush failed!");
     const stderr = &stderr_writer.interface;
     const args = try std.process.argsAlloc(allocator);
     defer std.process.argsFree(allocator, args);
@@ -89,7 +89,17 @@ const Substitution = struct {
 
 fn substituteLines(reader: *std.Io.Reader, writer: *std.Io.Writer, substitutions: []const Substitution) !usize {
     var subs: usize = 0;
-    while (reader.takeDelimiterExclusive('\n')) |line| {
+    var first_line = true;
+    while (reader.takeDelimiter('\n')) |line_opt| {
+        // takeDelimiter returns null at EOF
+        const line = line_opt orelse break;
+
+        // Write newline before each line except the first
+        if (!first_line) {
+            try writer.writeByte('\n');
+        }
+        first_line = false;
+
         var substituted = false;
         for (substitutions) |sub| {
             if (std.mem.eql(u8, line, sub.original)) {
@@ -101,9 +111,6 @@ fn substituteLines(reader: *std.Io.Reader, writer: *std.Io.Writer, substitutions
         }
         if (!substituted)
             try writer.writeAll(line);
-
-        if (reader.peekByte() != error.EndOfStream)
-            try writer.writeByte('\n');
     } else |err| if (err != error.EndOfStream) return err;
     return subs;
 }
@@ -120,7 +127,7 @@ test "substitute lines exact match" {
         .{ .original = "replace_me", .replacement = "new_line" },
     };
 
-    try substituteLines(
+    _ = try substituteLines(
         &input_stream,
         &output_stream,
         &substitutions,
@@ -141,7 +148,7 @@ test "no match found" {
         .{ .original = "nonexistent", .replacement = "replacement" },
     };
 
-    try substituteLines(
+    _ = try substituteLines(
         &input_stream,
         &output_stream,
         &substitutions,
@@ -163,7 +170,7 @@ test "partial match not replaced" {
         .{ .original = "match", .replacement = "replaced" },
     };
 
-    try substituteLines(
+    _ = try substituteLines(
         &input_stream,
         &output_stream,
         &substitutions,
@@ -186,7 +193,7 @@ test "multiple substitutions" {
         .{ .original = "replace_also", .replacement = "also_new" },
     };
 
-    try substituteLines(
+    _ = try substituteLines(
         &input_stream,
         &output_stream,
         &substitutions,