Config path builder

Build a nested settings document out of the flat path=value lines of an environment file.

Apply the assignments one by one, in order, to a document that starts as an empty object.

Path. A path is a key followed by any number of steps, each either .key (a field of an object) or [n] (an element of a list). A key is one or more of the characters A-Z a-z 0-9 _ -. An index n is 0, or a number from 1 to 99 without leading zeros. So a.b[2].c and grid[0][3] are valid, while x..y, [0]=1, k[01], k[100], k[a], a[0]b and paths with other characters are not. A line is split at its first =; everything after it is the value.

Rejected lines. A line with no = or with an invalid path is skipped and its position (0-based) is reported.

Value. true and false become booleans. 0, or an optional - followed by a number without leading zeros other than -0 itself, becomes an integer. Anything else, including the empty string, 007, -0, 1.5 and True, stays a string.

Assigning. Walk the path from the root, creating what is missing. A key step needs an object and an index step needs a list there; if the spot holds something else (a different kind of container, a string, a number, or null), it is replaced by a fresh empty object or list, and everything it contained is lost. A list that is too short is extended with null up to the index. The last step sets the value, replacing whatever was there.

Input: assignments, a list of strings.

Output: an object with two fields: "config", the final document, and "rejected", the positions of the skipped lines in increasing order.