From c4b2efb8aee4af0ef179a9b49ba401de3c4ef5d2 Mon Sep 17 00:00:00 2001
From: Eric Bartels <ebartels@gmail.com>
Date: Tue, 2 Jan 2024 08:26:14 -0800
Subject: Fix(black): formatting excluded files results in blank buffer (#254)

* Fix(black): formatting excluded files results in blank buffer (#249)

* Fixed stylua formatting

* Fixed more stylua formatting

* Log buffer name and change from trace to warning

* Test fix: set_formatter_output funtion was moved out of test_util

* Avoid blank output triggering errors in fuzzer tests
---
 tests/fuzzer_spec.lua |  7 +++++++
 tests/runner_spec.lua | 13 +++++++++++++
 2 files changed, 20 insertions(+)

(limited to 'tests')

diff --git a/tests/fuzzer_spec.lua b/tests/fuzzer_spec.lua
index fc68680..c47f1e5 100644
--- a/tests/fuzzer_spec.lua
+++ b/tests/fuzzer_spec.lua
@@ -97,6 +97,7 @@ describe("fuzzer", function()
   end
 
   local function make_edits(lines)
+    local was_empty = table.concat(lines):match("^%s*$")
     lines = vim.deepcopy(lines)
     for _ = 1, math.random(0, 3) do
       do_insert(lines)
@@ -107,6 +108,12 @@ describe("fuzzer", function()
     for _ = 1, math.random(0, 3) do
       do_delete(lines)
     end
+    -- avoid blank output (whitepsace only) which is ignored when applying formatting
+    if not was_empty then
+      while table.concat(lines):match("^%s*$") do
+        do_replace(lines)
+      end
+    end
     return lines
   end
 
diff --git a/tests/runner_spec.lua b/tests/runner_spec.lua
index 5ab7893..0c45117 100644
--- a/tests/runner_spec.lua
+++ b/tests/runner_spec.lua
@@ -307,6 +307,19 @@ print("a")
       assert.are.same({ "newcontent" }, vim.api.nvim_buf_get_lines(0, 0, -1, false))
     end)
 
+    it("discards formatting changes if formatter output is empty /w non-empty input", function()
+      local bufnr = vim.fn.bufadd("testfile")
+      vim.fn.bufload(bufnr)
+      vim.api.nvim_set_current_buf(bufnr)
+      local original_lines = { "line one", "line two" }
+      vim.api.nvim_buf_set_lines(bufnr, 0, -1, true, original_lines)
+      vim.bo[bufnr].modified = false
+      set_formatter_output({ "" })
+      conform.format({ formatters = { "test" }, quiet = true })
+      local output_lines = vim.api.nvim_buf_get_lines(0, 0, -1, false)
+      assert.are.same(original_lines, output_lines)
+    end)
+
     it("formats on save", function()
       conform.setup({
         formatters_by_ft = { ["*"] = { "test" } },
-- 
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