Replace tabs with spaces

src/Runic.jl

@@ -39,8 +39,8 @@ struct Node
     tags::TagType
 end
 
-function Node(head::JuliaSyntax.SyntaxHead, span::Integer)
-    return Node(head, span % UInt32, (), 0 % TagType)
+function Node(head::JuliaSyntax.SyntaxHead, span::Integer, tags::Integer = 0)
+    return Node(head, span % UInt32, (), tags % TagType)
 end
 
 function Node(head::JuliaSyntax.SyntaxHead, kids::Vector{Node})
@@ -78,6 +78,7 @@ JuliaSyntax.span(node::Node) = span(node)
 # Matching JuliaSyntax.(head|span|flags|kind)
 head(node::Node) = node.head
 span(node::Node) = node.span
+tags(node::Node) = node.tags
 flags(node::Node) = JuliaSyntax.flags(node)
 kind(node::Node) = JuliaSyntax.kind(node)
 
@@ -298,6 +299,7 @@ function format_node!(ctx::Context, node::Node)::Union{Node, Nothing, NullNode}
 
     # Go through the runestone and apply transformations.
     ctx.call_depth += 1
+    @return_something replace_tabs_with_four_spaces(ctx, node)
     @return_something no_leading_and_single_trailing_newline(ctx, node)
     @return_something max_three_consecutive_newlines(ctx, node)
     @return_something insert_delete_mark_newlines(ctx, node)

src/runestone.jl

@@ -25,6 +25,23 @@ function trim_trailing_whitespace(ctx::Context, node::Node)
     return node′
 end
 
+function replace_tabs_with_four_spaces(ctx::Context, node::Node)
+    kind(node) in KSet"Whitespace NewlineWs" || return nothing
+    @assert is_leaf(node)
+    bytes = read_bytes(ctx, node)
+    tabidx = findfirst(x -> x == UInt8('\t'), bytes)
+    tabidx === nothing && return nothing
+    while tabidx !== nothing
+        bytes[tabidx] = UInt8(' ')
+        for _ in 1:3
+            insert!(bytes, tabidx, UInt8(' '))
+        end
+        tabidx = findnext(x -> x == UInt8('\t'), bytes, tabidx + 4)
+    end
+    nb = replace_bytes!(ctx, bytes, span(node))
+    return Node(head(node), nb, tags(node))
+end
+
 function format_hex_literals(ctx::Context, node::Node)
     kind(node) === K"HexInt" || return nothing
     @assert flags(node) == 0

test/runtests.jl

@@ -769,3 +769,8 @@ end
         @test format_string("$(nl)"; filemode = true) == "\n"
     end
 end
+
+@testset "https://youtu.be/SsoOG6ZeyUI?si=xpKpnczuqsOThtFP" begin
+    @test format_string("f(a,\tb)") == "f(a, b)"
+    @test format_string("begin\n\tx = 1\nend") == "begin\n    x = 1\nend"
+end