Move std-rfc into Nushell (#15042)

Move `std-rfc` into Nushell.  `use std-rfc/<submodule>` now works "out-of-the-box"

crates/nu-std/std-rfc/str/mod.nu

@@ -0,0 +1,136 @@
+# Removes common indent from a multi-line string based on the number of spaces on the last line.
+# 
+# Example - Two leading spaces are removed from all lines:
+#
+# > let s = "
+#      Heading
+#        Indented Line
+#        Another Indented Line
+#
+#      Another Heading
+#      "
+# > $a | str dedent
+#
+# # => Heading
+# # =>   Indented Line
+# # =>   Another Indented Line
+# # => 
+# # => Another Heading
+export def dedent [
+    --tabs (-t)
+]: string -> string {
+    let string = $in
+
+    if ($string !~ $'^\s*(char lsep)') {
+        return (error make {
+            msg: 'First line must be empty'
+        })
+    }
+
+    if ($string !~ $'(char lsep)[ \t]*$') {
+        return (error make {
+            msg: 'Last line must contain only whitespace indicating the dedent'
+        })
+     }
+
+    # Get indent characters from the last line
+    let indent_chars = $string
+        | str replace -r $"\(?s\).*(char lsep)\([ \t]*\)$" '$1'
+
+    # Skip the first and last lines
+    let lines = (
+        $string
+        | lines
+        | skip
+        | # Only drop if there is whitespace. Otherwise, `lines`
+        | # drops a 0-length line anyway
+        | if ($indent_chars | str length) > 0 { drop } else {}
+        | enumerate
+        | rename lineNumber text
+    )
+
+    # Has to be done outside the replacement block or the error
+    # is converted to text. This is probably a Nushell bug, and
+    # this code can be recombined with the next iterator when
+    # the Nushell behavior is fixed.
+    for line in $lines {
+        # Skip lines with whitespace-only
+        if $line.text like '^\s*$' { continue }
+        # Error if any line doesn't start with enough indentation
+        if ($line.text | parse -r $"^\(($indent_chars)\)" | get capture0?.0?) != $indent_chars {
+            error make {
+                msg: $"Line ($line.lineNumber + 1) must have an indent of ($indent_chars | str length) or more."
+            }
+        }
+    }
+
+    $lines
+    | each {|line|
+        # Don't operate on lines containing only whitespace
+        if ($line.text not-like '^\s*$') {
+            $line.text | str replace $indent_chars ''
+        } else {
+            $line.text
+        }
+      }
+    | str join (char line_sep)
+}
+
+# Remove common indent from a multi-line string based on the line with the smallest indent
+# 
+# Example - Two leading spaces are removed from all lines:
+#
+# > let s = "
+#      Heading
+#        Indented Line
+#        Another Indented Line
+#
+#      Another Heading
+#   "
+# > $a | str dedent
+#
+# # => Heading
+# # =>   Indented Line
+# # =>   Another Indented Line
+# # =>
+# # => Another Heading
+#
+export def unindent [
+    --tabs (-t)            # String uses tabs instead of spaces for indentation
+]: string -> string {
+    let indent_char = match $tabs {
+        true => '\t'
+        false => ' '
+    }
+
+    let text = (
+        $in
+        | # Remove the first line if it is only whitespace (tabs or spaces)
+        | str replace -r $'^[ \t]*(char lsep)' ''
+        | # Remove the last line if it is only whitespace (tabs or spaces)
+        | str replace -r $'(char lsep)[ \t]*$' ''
+    )
+
+    # Early return if there is only a single, empty (other than whitespace) line
+    if ($text like '^[ \t]*$') {
+        return $text
+    }
+
+    let minimumIndent = (
+        $text
+        | lines
+        | # Ignore indentation in any line that is only whitespace
+        | where $it not-like '^[ \t]*$'
+        | # Replaces the text with its indentation
+        | each {
+            str replace -r $"^\(($indent_char)*\).*" '$1'
+            | str length
+        }
+        | math min
+    )
+
+    let indent_chars = ('' | fill -c $indent_char -w $minimumIndent)
+
+    $text
+    | str replace -r --all $"\(?m\)^($indent_chars)" ''
+}