% File src/library/utils/man/news.Rd
% Part of the R package, https://www.R-project.org
% Copyright 1995-2020 R Core Team
% Distributed under GPL 2 or later

\name{news}
\title{Build and Query R or Package News Information}
\alias{news}
\alias{print.news_db}
\description{
  Build and query the news data base for \R or add-on packages.
}
\usage{
news(query, package = "R", lib.loc = NULL, format = NULL,
     reader = NULL, db = NULL)

\S3method{print}{news_db}(x, doBrowse = interactive(),
      browser = getOption("browser"), \dots)
}
\arguments{
  \item{query}{an expression for selecting news entries}
  \item{package}{a character string giving the name of an installed
    add-on package, or \code{"R"} or \code{"R-3"} or \code{"R-2"}}.
  \item{lib.loc}{a character vector of directory names of R libraries,
    or \code{NULL}.  The default value of \code{NULL} corresponds to all
    libraries currently known.}
  \item{format}{Not yet used.}
  \item{reader}{Not yet used.}
  \item{db, x}{a news db obtained from \code{news()}.}

  \item{doBrowse}{logical specifying that the news should be opened in
    the browser (by \code{\link{browseURL}}, accessible as via
    \code{\link{help.start}}) instead of printed to the console.}
  \item{browser}{the browser to be used, see \code{\link{browseURL}}.}
  \item{\dots}{potentially further arguments passed to \code{print()}.}
}
\value{
  A data frame inheriting from class \code{"news_db"}, with
  \code{\link{attributes}} \code{"package"} (and \code{"subset"} if the
  \code{query} lead to proper subsetting).
}
\details{
  If \code{package} is \code{"R"} (default), a news db is built with the
  news since the 4.0.0 release of \R (corresponding to \R's top-level
  \file{NEWS} file). For \code{"R-3"} or \code{"R-2"}. news for \R 3.x.y
  or \R 2.x.y respectively.  Otherwise, if the given add-on package can
  be found in the given libraries, it is attempted to read its news in
  structured form from files \file{inst/NEWS.Rd}, \file{NEWS.md} (since
  \R version 3.6.0, needs packages \CRANpkg{commonmark} and
  \CRANpkg{xml2} to be available), \file{NEWS} or \file{inst/NEWS} (in
  that order).

  File \file{inst/NEWS.Rd} should be an Rd file given the entries as Rd
  \verb{\itemize} lists, grouped according to version using
  \verb{section} elements with names starting with a suitable prefix
  (e.g.\sspace{}\dQuote{Changes in version}) followed by a space and the version
  number, and optionally followed by a space and a parenthesized ISO
  8601 (\%Y-\%m-\%d, see \code{\link{strptime}}) format date, and
  possibly further grouped according to categories using
  \verb{\subsection} elements named as the categories.
  At the very end of \verb{\section{..}}, the date may also be specified
  as \verb{(\%Y-\%m-\%d, <note>)}, i.e., including parentheses.

  File \file{NEWS.md} should contain the news in Markdown (following the
  CommonMark (\url{https://commonmark.org/}) specification), with the
  primary heading level giving the version number after a prefix
  followed by a space, and optionally followed by a space and a
  parenthesized ISO 8601 format date.  Where available, secondary
  heading are taken to indicate categories.  To accommodate for common
  practice, news entries are only split down to the category level.

  The plain text \file{NEWS} files in add-on packages use a variety of
  different formats; the default news reader should be capable to
  extract individual news entries from a majority of packages from the
  standard repositories, which use (slight variations of) the following
  format:

  \itemize{
    \item Entries are grouped according to version, with version header
    \dQuote{Changes in version} at the beginning of a line, followed by
    a version number, optionally followed by an ISO 8601 format date,
    possibly parenthesized.
    \item Entries may be grouped according to category, with a category
    header (different from a version header) starting at the beginning
    of a line.
    \item Entries are written as itemize-type lists, using one of
    \samp{o}, \samp{*}, \samp{-} or \samp{+} as item tag.  Entries must
    be indented, and ideally use a common indentation for the item
    texts.
  }

  Additional formats and readers may be supported in the future.

  Package \pkg{tools} provides an (internal) utility function
  \code{news2Rd} to convert plain text \file{NEWS} files to Rd.  For
  \file{NEWS} files in a format which can successfully be handled by the
  default reader, package maintainers can use
  \code{tools:::news2Rd(dir, "NEWS.Rd")},
  possibly with additional argument \code{codify = TRUE},
  with \code{dir} a character string specifying the path to a package's
  root directory.  Upon success, the \file{NEWS.Rd} file can further be
  improved and then be moved to the \file{inst} subdirectory of the
  package source directory.

  The news db built is a character data frame inheriting from
  \code{"news_db"} with variables \code{Version}, \code{Category},
  \code{Date} and \code{Text}, where the last contains the entry texts
  read, and the other variables may be \code{NA} if they were missing or
  could not be determined.

  Using \code{query}, one can select news entries from the db.  If
  missing or \code{NULL}, the complete db is returned.  Otherwise,
  \code{query} should be an expression involving (a subset of) the
  variables \code{Version}, \code{Category}, \code{Date} and
  \code{Text}, and when evaluated within the db returning a logical
  vector with length the number of entries in the db.  The entries for
  which evaluation gave \code{TRUE} are selected.  When evaluating,
  \code{Version} and \code{Date} are coerced to
  \code{\link{numeric_version}} and \code{\link{Date}} objects,
  respectively, so that the comparison operators for these classes can
  be employed.
}

\examples{
## Build a db of all R news entries.
db <- news()
\dontshow{
  vv <- capture.output(print(db, doBrowse=FALSE))  # without an error
  stopifnot(is.character(vv), length(vv) >= 3) # was wrong (for weeks during devel.)
}
## Bug fixes with PR number in 4.0.0.
db4 <- news(Version == "4.0.0" & grepl("^BUG", Category) & grepl("PR#", Text),
            db = db)
nrow(db4)
%% Maybe reinstate after release when number is stable
%% \dontrun{stopifnot( !any(attr(db4,"bad")) && nrow(db4) == 19 )}

## print db4 to show in an HTML browser.

## News from a date range ('Matrix' is there in a regular R installation):
if(length(iM <- find.package("Matrix", quiet = TRUE)) && nzchar(iM)) {
   dM <- news(package="Matrix")
   stopifnot(identical(dM, news(db=dM)))
   dM2014 <- news("2014-01-01" <= Date & Date <= "2014-12-31", db = dM)
   stopifnot(paste0("1.1-", 2:4) \%in\% dM2014[,"Version"])
}

## Which categories have been in use? % R-core maybe should standardize a bit more
sort(table(db[, "Category"]), decreasing = TRUE)
## Entries with version >= 4.0.0
table(news(Version >= "4.0.0", db = db)$Version)

\donttest{
## do the same for R 3.x.y, more slowly
db3 <- news(package = "R-3")
sort(table(db3[, "Category"]), decreasing = TRUE)
## Entries with version >= 3.6.0
table(news(Version >= "3.6.0", db = db3)$Version)
}
}