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Add support for preserve_single_line_if::Bool #937

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5d0295e
Add support for `preserve_single_line_if = x::Bool`
alexandergunnarson Aug 8, 2025
516c505
Update options.jl
alexandergunnarson Aug 8, 2025
d9839df
Keep default
alexandergunnarson Aug 14, 2025
8ebd28a
Merge branch 'master' into patch-1
penelopeysm May 27, 2026
cae12ce
Fix preserve_single_line_if and add tests
alexandergunnarson May 28, 2026
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1 change: 1 addition & 0 deletions src/options.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -36,6 +36,7 @@ Base.@kwdef struct Options
yas_style_nesting::Bool = false
short_circuit_to_if::Bool = false
disallow_single_arg_nesting::Bool = false
preserve_single_line_if::Bool = false

function Options(args...)
opts = new(args...)
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57 changes: 49 additions & 8 deletions src/styles/default/pretty.jl
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Expand Up @@ -1852,27 +1852,68 @@ function p_if(
return t
end

preserve_single_line =
s.opts.preserve_single_line_if &&
on_same_line(s, s.offset, s.offset + span(cst) - 1)

is_first = true

for c in children(cst)
if kind(c) in KSet"if elseif else"
if !haschildren(c)
add_node!(t, pretty(style, c, s, ctx, lineage), s; max_padding = 0)
if preserve_single_line && !is_first
add_node!(t, Whitespace(1), s)
end
add_node!(
t,
pretty(style, c, s, ctx, lineage),
s;
max_padding = if preserve_single_line
-1
else
0
end,
join_lines = preserve_single_line && !is_first,
)
else
len = length(t)
n = pretty(style, c, s, ctx, lineage)
add_node!(t, n, s)
if preserve_single_line && !is_first
add_node!(t, Whitespace(1), s)
end
add_node!(t, n, s; join_lines = preserve_single_line && !is_first)
t.len = max(len, length(n))
end
is_first = false
elseif kind(c) === K"end"
add_node!(t, pretty(style, c, s, ctx, lineage), s)
elseif kind(c) === K"block"
s.indent += s.opts.indent
if preserve_single_line
add_node!(t, Whitespace(1), s)
end
add_node!(
t,
pretty(style, c, s, newctx(ctx; ignore_single_line = true), lineage),
pretty(style, c, s, ctx, lineage),
s;
max_padding = s.opts.indent,
join_lines = preserve_single_line,
)
s.indent -= s.opts.indent
elseif kind(c) === K"block"
if preserve_single_line
add_node!(t, Whitespace(1), s)
add_node!(
t,
pretty(style, c, s, ctx, lineage),
s;
join_lines = true,
)
else
s.indent += s.opts.indent
add_node!(
t,
pretty(style, c, s, newctx(ctx; ignore_single_line = true), lineage),
s;
max_padding = s.opts.indent,
)
s.indent -= s.opts.indent
end
elseif !JuliaSyntax.is_whitespace(c)
add_node!(t, Whitespace(1), s)
add_node!(t, pretty(style, c, s, ctx, lineage), s; join_lines = true)

@penelopeysm penelopeysm May 28, 2026 •
edited
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(If you agree with (2), then I believe this is the appropriate fix:)

Suggested change
add_node!(t, pretty(style, c, s, ctx, lineage), s; join_lines = true)
ctx2 = preserve_single_line_if ? newctx(ctx; nonest=true) : ctx
add_node!(t, pretty(style, c, s, ctx2, lineage), s; join_lines = true)

@penelopeysm penelopeysm May 28, 2026

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(1) looks trickier to accomplish to me. I haven't attempted to figure out how that would be done.

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71 changes: 71 additions & 0 deletions test/options.jl
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Expand Up @@ -2644,4 +2644,75 @@
"""
@test fmt(s1, 2, 1; disallow_single_arg_nesting = true) == s2
end

@testset "preserve single line if" begin
# Basic single-line if is preserved
str = "if x > 0 return 1 end"
@test fmt(str; preserve_single_line_if = true) == str

# Single-line if is expanded when option is false (default)
str_ = "if x > 0 return 1 end"
str = """
if x > 0
return 1
end"""
@test fmt(str_; preserve_single_line_if = false) == str
@test fmt(str_) == str

# Multi-line if is not affected by the option
str = """
if x > 0
return 1
end
"""
@test fmt(str; preserve_single_line_if = true) == str

# Single-line if-else
str = "if x > 0 1 else 2 end"
@test fmt(str; preserve_single_line_if = true) == str

# Single-line if-elseif-else
str = "if x > 0 1 elseif x < 0 2 else 0 end"
@test fmt(str; preserve_single_line_if = true) == str

# Multi-line if-else is not affected
str = """
if x > 0
return 1
else
return 2
end
"""
@test fmt(str; preserve_single_line_if = true) == str

# Nested single-line if
str = "if x > 0 if y > 0 return 1 end end"
@test fmt(str; preserve_single_line_if = true) == str

# Inside a function
str = """
function f()
if rand() < 0.5 return 2 end
0
end
"""
@test fmt(str; preserve_single_line_if = true) == str

# Inside a function, expanded when option is false
str_ = """
function f()
if rand() < 0.5 return 2 end
0
end
"""
str = """
function f()
if rand() < 0.5
return 2
end
0
end
"""
@test fmt(str_; preserve_single_line_if = false) == str
end
end
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