Asti's Notes
FP, Rx, EDA
A git-config parser
A line-by-line parser in F#

Reading .git/config is the fastest way of getting info on a repository and its dependencies.

The Spec

Let's start by going through the spec from https://git-scm.com/docs/git-config#_syntax

An example config:

# Core variables
[core]
	; Don't trust file modes
	filemode = false

# Our diff algorithm
[branch "master"]	
	use = true

The basics:

The # and ; characters begin comments to the end of line, blank lines are ignored.

let isComment (line:string) = line.StartsWith(';') || line.StartsWith('#') || String.IsNullOrWhiteSpace(line)

The file consists of sections and variables. A section begins with the name of the section in square brackets and continues until the next section begins.

let isSectionHeader (line:string) = line.StartsWith("[") && line.EndsWith("]")

Sections can be further divided into subsections. To begin a subsection put its name in double quotes, separated by space from the section name, in the section header.

let splitSectionHeader (line:string) = 
    line.Split([|' '|], 2) |> Array.map(fun s -> s.Trim('[',']', ' ', '"'))

Construction

What we want is a seq of ConfigSection

type ConfigSection = { Name: string; Subsection: string; Values: Map<string,string> }

The file is sequence of lines, but when we encounter a section header, all subsequent lines under it have to be grouped into that section - till the next section header is encountered.

We can do that by carrying the section header with every line until we swap out to a new section header.

Seq.scan (fun (section, prev) line -> 
	if isSectionHeader line then 
		(line, line)                        
	else
		(section, line)
) ("", "")

So this is going to be our example up top:

("","")
("core", "core")
("core", "filemode = false")

Now if we do a Seq.groupBy fst, we have our values grouped under our sections.

Here's the whole implementation:


Last modified on 2019-09-24

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