add `alignTable`, `parseTableCells` to align/format a tab(etc) delimited table (#10182)

* add compiler/unittest_light.nim for easy diffing: assertEquals and mismatch
* fixup
* add alignTable, parseTableCells

2 files changed, 120 insertions, 0 deletions

diff --git a/compiler/asciitables.nim b/compiler/asciitables.nim
new file mode 100644
index 000000000..c25d54bde
--- /dev/null
+++ b/compiler/asciitables.nim
@@ -0,0 +1,83 @@
+#[
+move to std/asciitables.nim once stable, or to a nimble paackage
+once compiler can depend on nimble
+]#
+
+type Cell* = object
+  text*: string
+  width*, row*, col*, ncols*, nrows*: int
+
+iterator parseTableCells*(s: string, delim = '\t'): Cell =
+  ## iterates over all cells in a `delim`-delimited `s`, after a 1st
+  ## pass that computes number of rows, columns, and width of each column.
+  var widths: seq[int]
+  var cell: Cell
+  template update() =
+    if widths.len<=cell.col:
+      widths.setLen cell.col+1
+      widths[cell.col] = cell.width
+    else:
+      widths[cell.col] = max(widths[cell.col], cell.width)
+    cell.width = 0
+
+  for a in s:
+    case a
+    of '\n':
+      update()
+      cell.col = 0
+      cell.row.inc
+    elif a == delim:
+      update()
+      cell.col.inc
+    else:
+      # todo: consider multi-width chars when porting to non-ascii implementation
+      cell.width.inc
+  if s.len > 0 and s[^1] != '\n':
+    update()
+
+  cell.ncols = widths.len
+  cell.nrows = cell.row + 1
+  cell.row = 0
+  cell.col = 0
+  cell.width = 0
+
+  template update2() =
+    cell.width = widths[cell.col]
+    yield cell
+    cell.text = ""
+    cell.width = 0
+    cell.col.inc
+
+  template finishRow() =
+    for col in cell.col..<cell.ncols:
+      cell.col = col
+      update2()
+    cell.col = 0
+
+  for a in s:
+    case a
+    of '\n':
+      finishRow()
+      cell.row.inc
+    elif a == delim:
+      update2()
+    else:
+      cell.width.inc
+      cell.text.add a
+
+  if s.len > 0 and s[^1] != '\n':
+    finishRow()
+
+proc alignTable*(s: string, delim = '\t', fill = ' ', sep = " "): string =
+  ## formats a `delim`-delimited `s` representing a table; each cell is aligned
+  ## to a width that's computed for each column; consecutive columns are
+  ## delimted by `sep`, and alignment space is filled using `fill`.
+  ## More customized formatting can be done by calling `parseTableCells` directly.
+  for cell in parseTableCells(s, delim):
+    result.add cell.text
+    for i in cell.text.len..<cell.width:
+      result.add fill
+    if cell.col < cell.ncols-1:
+      result.add sep
+    if cell.col == cell.ncols-1 and cell.row < cell.nrows - 1:
+      result.add '\n'
diff --git a/compiler/unittest_light.nim b/compiler/unittest_light.nim
new file mode 100644
index 000000000..bcba6f7c7
--- /dev/null
+++ b/compiler/unittest_light.nim
@@ -0,0 +1,37 @@
+# note: consider merging tests/assert/testhelper.nim here.
+
+proc mismatch*[T](lhs: T, rhs: T): string =
+  ## Simplified version of `unittest.require` that satisfies a common use case,
+  ## while avoiding pulling too many dependencies. On failure, diagnostic
+  ## information is provided that in particular makes it easy to spot
+  ## whitespace mismatches and where the mismatch is.
+  proc replaceInvisible(s: string): string =
+    for a in s:
+      case a
+      of '\n': result.add "\\n\n"
+      else: result.add a
+
+  proc quoted(s: string): string = result.addQuoted s
+
+  result.add "\n"
+  result.add "lhs:{\n" & replaceInvisible(
+      $lhs) & "}\nrhs:{\n" & replaceInvisible($rhs) & "}\n"
+  when compiles(lhs.len):
+    if lhs.len != rhs.len:
+      result.add "lhs.len: " & $lhs.len & " rhs.len: " & $rhs.len & "\n"
+    when compiles(lhs[0]):
+      var i = 0
+      while i < lhs.len and i < rhs.len:
+        if lhs[i] != rhs[i]: break
+        i.inc
+      result.add "first mismatch index: " & $i & "\n"
+      if i < lhs.len and i < rhs.len:
+        result.add "lhs[i]: {" & quoted($lhs[i]) & "} rhs[i]: {" & quoted(
+            $rhs[i]) & "}"
+      result.add "lhs[0..<i]:{\n" & replaceInvisible($lhs[
+          0..<i]) & "}\nrhs[0..<i]:{\n" & replaceInvisible($rhs[0..<i]) & "}"
+
+proc assertEquals*[T](lhs: T, rhs: T) =
+  when false: # can be useful for debugging to see all that's fed to this.
+    echo "----" & $lhs
+  doAssert lhs==rhs, mismatch(lhs, rhs)