Fix layout of REPL completions with newlines

Co-authored-by: Jameson Nash <[email protected]>

stdlib/REPL/src/LineEdit.jl

@@ -322,23 +322,28 @@ end
 
 # Show available completions
 function show_completions(s::PromptState, completions::Vector{String})
-    colmax = maximum(map(length, completions))
-    num_cols = max(div(width(terminal(s)), colmax+2), 1)
-    entries_per_col, r = divrem(length(completions), num_cols)
-    entries_per_col += r != 0
     # skip any lines of input after the cursor
     cmove_down(terminal(s), input_string_newlines_aftercursor(s))
     println(terminal(s))
-    for row = 1:entries_per_col
-        for col = 0:num_cols
-            idx = row + col*entries_per_col
-            if idx <= length(completions)
-                cmove_col(terminal(s), (colmax+2)*col+1)
+    if any(Base.Fix1(occursin, '\n'), completions)
+        foreach(Base.Fix1(println, terminal(s)), completions)
+    else
+        colmax = 2 + maximum(length, completions; init=1) # n.b. length >= textwidth
+        num_cols = max(div(width(terminal(s)), colmax), 1)
+        n = length(completions)
+        entries_per_col = cld(n, num_cols)
+        idx = 0
+        for _ in 1:entries_per_col
+            for col = 0:(num_cols-1)
+                idx += 1
+                idx > n && break
+                cmove_col(terminal(s), colmax*col+1)
                 print(terminal(s), completions[idx])
             end
+            println(terminal(s))
         end
-        println(terminal(s))
     end
+
     # make space for the prompt
     for i = 1:input_string_newlines(s)
         println(terminal(s))

stdlib/REPL/test/lineedit.jl

@@ -906,3 +906,17 @@ end
     @test get_last_word("a[b[]]") == "b"
     @test get_last_word("a[]") == "a[]"
 end
+
+@testset "issue #45836" begin
+    term = FakeTerminal(IOBuffer(), IOBuffer(), IOBuffer())
+    promptstate = REPL.LineEdit.init_state(term, REPL.LineEdit.mode(new_state()))
+    strings = ["abcdef", "123456", "ijklmn"]
+    REPL.LineEdit.show_completions(promptstate, strings)
+    completion = String(take!(term.out_stream))
+    @test completion == "\033[0B\n\rabcdef\r\033[8C123456\r\033[16Cijklmn\n"
+    strings2 = ["abcdef", "123456\nijklmn"]
+    promptstate = REPL.LineEdit.init_state(term, REPL.LineEdit.mode(new_state()))
+    REPL.LineEdit.show_completions(promptstate, strings2)
+    completion2 = String(take!(term.out_stream))
+    @test completion2 == "\033[0B\nabcdef\n123456\nijklmn\n"
+end