source: ps/trunk/build/premake/premake5/scripts/changes.lua

---
-- Output a list of merged PRs since last release in the CHANGES.txt format.
---

local usage = "Usage: premake5 --file=scripts/changes.lua --since=<rev> changes"

local sinceRev = _OPTIONS["since"]

if not sinceRev then
    print(usage)
    error("Missing `--since`", 0)
end


local function parsePullRequestId(line)
    return line:match("#%d+%s")
end

local function parseTitle(line)
    return line:match("||(.+)")
end

local function parseAuthor(line)
    return line:match("%s([^%s]-)/")
end

local function parseLog(line)
    local pr = parsePullRequestId(line)
    local title = parseTitle(line)
    local author = parseAuthor(line)
    return string.format("* PR %s %s (@%s)", pr, title, author)
end


local function gatherChanges()
    local cmd = string.format('git log HEAD "^%s" --merges --first-parent --format="%%s||%%b"', _OPTIONS["since"])
    local output = os.outputof(cmd)

    changes = {}

    for line in output:gmatch("[^\r\n]+") do
        table.insert(changes, parseLog(line))
    end

    return changes
end


local function generateChanges()
    local changes = gatherChanges()
    table.sort(changes)
    for i = 1, #changes do
        print(changes[i])
    end
end


newaction {
    trigger = "changes",
    description = "Generate list of git merges in CHANGES.txt format",
    execute = generateChanges
}

newoption {
    trigger = "since",
    value = "revision",
    description = "Log merges since this revision"
}