replace ArrayLists with bounded storage

1 files changed, 27 insertions, 9 deletions

diff --git a/mupdf.zig b/mupdf.zig
index c80f678d..a407ea09 100644
--- a/mupdf.zig
+++ b/mupdf.zig
@@ -248,17 +248,23 @@ fn flatCSources(b: *std.Build, io: std.Io, dependency: *std.Build.Dependency, re
         std.debug.panic("MuPDF source directory is missing: {s}", .{relative_dir});
     defer dir.close(io);
 
-    var files: std.ArrayList([]const u8) = .empty;
+    const max_flat_sources = 4096;
+    var bounded: [max_flat_sources][]const u8 = undefined;
+    var count: usize = 0;
     var it = dir.iterate();
     while (it.next(io) catch @panic("read MuPDF source directory")) |entry| {
         // Some filesystems report d_type as unknown. The selected directories
         // are flat and immutable, so the suffix is the reliable predicate.
         if (!std.mem.endsWith(u8, entry.name, ".c")) continue;
-        files.append(b.allocator, b.fmt("{s}/{s}", .{ relative_dir, entry.name })) catch @panic("OOM");
+        if (count == bounded.len) std.debug.panic("MuPDF source directory exceeds {d} C files: {s}", .{ bounded.len, relative_dir });
+        bounded[count] = b.fmt("{s}/{s}", .{ relative_dir, entry.name });
+        count += 1;
     }
-    std.mem.sort([]const u8, files.items, {}, lessThan);
-    if (files.items.len == 0) std.debug.panic("MuPDF source directory has no C files: {s}", .{relative_dir});
-    return files.items;
+    if (count == 0) std.debug.panic("MuPDF source directory has no C files: {s}", .{relative_dir});
+    const files = b.allocator.alloc([]const u8, count) catch @panic("OOM");
+    @memcpy(files, bounded[0..count]);
+    std.mem.sort([]const u8, files, {}, lessThan);
+    return files;
 }
 
 fn readMakelists(b: *std.Build, io: std.Io, dependency: *std.Build.Dependency) []const u8 {
@@ -271,7 +277,7 @@ fn readMakelists(b: *std.Build, io: std.Io, dependency: *std.Build.Dependency) [
 }
 
 fn makeSources(b: *std.Build, makelists: []const u8, variable: []const u8) []const []const u8 {
-    var files: std.ArrayList([]const u8) = .empty;
+    var count: usize = 0;
     var lines = std.mem.splitScalar(u8, makelists, '\n');
     while (lines.next()) |raw_line| {
         const line = std.mem.trim(u8, raw_line, " \t\r");
@@ -279,11 +285,23 @@ fn makeSources(b: *std.Build, makelists: []const u8, variable: []const u8) []con
         const assignment = std.mem.trimStart(u8, line[variable.len..], " \t");
         if (!std.mem.startsWith(u8, assignment, "+=")) continue;
         const path = std.mem.trim(u8, assignment[2..], " \t\r");
+        if (std.mem.endsWith(u8, path, ".c")) count += 1;
+    }
+    if (count == 0) std.debug.panic("MuPDF Makelists variable has no C sources: {s}", .{variable});
+    const files = b.allocator.alloc([]const u8, count) catch @panic("OOM");
+    lines = std.mem.splitScalar(u8, makelists, '\n');
+    var file_i: usize = 0;
+    while (lines.next()) |raw_line| {
+        const line = std.mem.trim(u8, raw_line, " \t\r");
+        if (!std.mem.startsWith(u8, line, variable)) continue;
+        const assignment = std.mem.trimStart(u8, line[variable.len..], " \t");
+        if (!std.mem.startsWith(u8, assignment, "+=")) continue;
+        const path = std.mem.trim(u8, assignment[2..], " \t\r");
         if (!std.mem.endsWith(u8, path, ".c")) continue;
-        files.append(b.allocator, b.dupe(path)) catch @panic("OOM");
+        files[file_i] = b.dupe(path);
+        file_i += 1;
     }
-    if (files.items.len == 0) std.debug.panic("MuPDF Makelists variable has no C sources: {s}", .{variable});
-    return files.items;
+    return files;
 }
 
 fn lessThan(_: void, a: []const u8, b: []const u8) bool {