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zig fmt incorrectly allows extra newlines at end of file #2074

andrewrk opened this Issue Mar 18, 2019 · 2 comments


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andrewrk commented Mar 18, 2019

Here's a (currently failing) test to go in std/zig/parser_test.zig:

test "zig fmt: extra newlines at the end" {
    try testTransform(
        \\const a = b;
        \\const a = b;

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shawnl commented Mar 21, 2019

How should zig fmt handle extra newlines inside the file? Should reduce more than two adjacent newlines to two, except at the end, where only one is allowed?


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andrewrk commented Mar 21, 2019

Should reduce more than two adjacent newlines to two, except at the end, where only one is allowed?

Correct. This behavior is already implemented, except for the end. I believe the problem is actually in the detection of changes:


Lines 36 to 62 in b5cc92f

if (!self.anything_changed_ptr.*) {
const end = self.source_index + bytes.len;
if (end > self.source.len) {
self.anything_changed_ptr.* = true;
} else {
const src_slice = self.source[self.source_index..end];
self.source_index += bytes.len;
if (!mem.eql(u8, bytes, src_slice)) {
self.anything_changed_ptr.* = true;
try self.child_stream.write(bytes);
var my_stream = MyStream{
.stream = MyStream.Stream{ .writeFn = MyStream.write },
.child_stream = stream,
.anything_changed_ptr = &anything_changed,
.source_index = 0,
.source = tree.source,
try renderRoot(allocator, &, tree);
return anything_changed;

I think this logic is simply missing a check for source_index not matching source.len and marking anything_changed as true in this case.

andrewrk added a commit that referenced this issue Mar 26, 2019

fmt: check for extra newline at end of file
`anything_changed` checks if `source_index` == `source.len`
Fixes #2074

@andrewrk andrewrk modified the milestones: 0.5.0, 0.4.0 Apr 8, 2019

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