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zig fmt: avoid unnecessary file system access

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zig fmt previously would write a temp file, and then either rename it
into place if necessary, or unlink it if nothing was changed. Now zig
fmt renders into a memory buffer, and only writes the temp file and
renames it into place if anything changed.

Based on the performance testing I did this actually did not have much
of an impact, however it's likely that on other operating systems and
other hard drives this could make a big difference.
This commit is contained in:
Andrew Kelley 2020-06-20 20:14:33 -04:00
parent 0a9672fb86
commit 64dfd1883e
1 changed files with 16 additions and 7 deletions
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23
src-self-hosted/main.zig
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@ -546,6 +546,7 @@ const Fmt = struct {
any_error: bool,
color: Color,
gpa: *Allocator,
out_buffer: std.ArrayList(u8),
const SeenMap = std.AutoHashMap(fs.File.INode, void);
};
@ -641,7 +642,10 @@ pub fn cmdFmt(gpa: *Allocator, args: []const []const u8) !void {
.seen = Fmt.SeenMap.init(gpa),
.any_error = false,
.color = color,
.out_buffer = std.ArrayList(u8).init(gpa),
};
defer fmt.seen.deinit();
defer fmt.out_buffer.deinit();
for (input_files.span()) |file_path| {
// Get the real path here to avoid Windows failing on relative file paths with . or .. in them.
@ -767,14 +771,19 @@ fn fmtPathFile(
fmt.any_error = true;
}
} else {
const baf = try io.BufferedAtomicFile.create(fmt.gpa, dir, sub_path, .{ .mode = stat.mode });
defer baf.destroy();
// As a heuristic, we make enough capacity for the same as the input source.
try fmt.out_buffer.ensureCapacity(source_code.len);
fmt.out_buffer.items.len = 0;
const anything_changed = try std.zig.render(fmt.gpa, fmt.out_buffer.writer(), tree);
if (!anything_changed)
return; // Good thing we didn't waste any file system access on this.
const anything_changed = try std.zig.render(fmt.gpa, baf.stream(), tree);
if (anything_changed) {
std.debug.warn("{}\n", .{file_path});
try baf.finish();
}
var af = try dir.atomicFile(sub_path, .{ .mode = stat.mode });
defer af.deinit();
try af.file.writeAll(fmt.out_buffer.items);
try af.finish();
std.debug.warn("{}\n", .{file_path});
}
}