fix(text) dedent now handles declining indents and empty lines

Also adds two tests for indent/dedent regaring newlines added

3 files changed, 58 insertions, 4 deletions

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 5ae62df..c21a1a6 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -11,6 +11,8 @@ see [CONTRIBUTING.md](CONTRIBUTING.md#release-instructions-for-a-new-version) fo
    [#387](https://github.com/lunarmodules/Penlight/pull/387)
  - fix: `xml.maptags` would hang if it encountered text-nodes
    [#396](https://github.com/lunarmodules/Penlight/pull/396)
+ - fix: `text.dedent` didn't handle declining indents nor empty lines
+   [#402](https://github.com/lunarmodules/Penlight/pull/402)
 
 ## 1.11.0 (2021-08-18)
 
diff --git a/lua/pl/text.lua b/lua/pl/text.lua
index 1ebdd29..35232c8 100644
--- a/lua/pl/text.lua
+++ b/lua/pl/text.lua
@@ -52,14 +52,40 @@ end
 
 --- dedent a multiline string by removing any initial indent.
 -- useful when working with [[..]] strings.
+-- Empty lines are ignored.
 -- @tparam string s the (multiline) string
 -- @return a string with initial indent zero.
+-- @usage
+-- local s = dedent [[
+--          One
+--
+--        Two
+--
+--      Three
+-- ]]
+-- assert(s == [[
+--     One
+--
+--   Two
+--
+-- Three
+-- ]])
 function text.dedent (s)
     assert_arg(1,s,'string')
-    local sl = split(s,'\n')
-    local _,i2 = (#sl>0 and sl[1] or ''):find('^%s*')
-    sl = imap(string.sub,sl,i2+1)
-    return concat(sl,'\n')..'\n'
+    local lst = split(s,'\n')
+    if #lst>0 then
+      local ind_size = math.huge
+      for i, line in ipairs(lst) do
+        local i1, i2 = lst[i]:find('^%s*[^%s]')
+        if i1 and i2 < ind_size then
+          ind_size = i2
+        end
+      end
+      for i, line in ipairs(lst) do
+        lst[i] = lst[i]:sub(ind_size, -1)
+      end
+    end
+    return concat(lst,'\n')..'\n'
 end
 
 --- format a paragraph into lines so that they fit into a line width.
diff --git a/spec/text_spec.lua b/spec/text_spec.lua
index d50624f..095afb8 100644
--- a/spec/text_spec.lua
+++ b/spec/text_spec.lua
@@ -66,6 +66,11 @@ end
 ]], text.indent("easy\n\nenough!", 2 ,'*'))
     end)
 
+    it("indent() appends a newline if not present", function()
+      assert.equal("  hello\n  world\n", text.indent("hello\nworld", 2))
+      assert.equal("  hello\n  world\n", text.indent("hello\nworld\n", 2))
+    end)
+
 
     it("dedent() removes prefixed whitespace", function()
       assert.equal([[
@@ -79,6 +84,27 @@ three
 ]])
     end)
 
+    it("dedent() removes prefixed whitespace, retains structure", function()
+      assert.equal([[
+  one
+
+ two
+
+three
+]], text.dedent [[
+      one
+
+     two
+
+    three
+]])
+    end)
+
+    it("dedent() appends a newline if not present", function()
+      assert.equal("hello\nworld\n", text.dedent("  hello\n  world"))
+      assert.equal("hello\nworld\n", text.dedent("  hello\n  world\n"))
+    end)
+
 
     it("fill()/wrap() word-wraps a text", function()
       assert.equal([[