From 791bd3a98e84ce2fe6ce1679fe3c1f23a1ae7d22 Mon Sep 17 00:00:00 2001
From: James Lamb <jaylamb20@gmail.com>
Date: Sun, 8 Dec 2024 22:38:20 -0600
Subject: [PATCH] more changes, better docs

---
 .ci/download-r-revdeps.R             |  4 ++--
 .ci/run-revdep-checks.sh             | 11 ++++++++---
 .github/workflows/r_revdepchecks.yml | 12 ++----------
 R-package/R/lgb.train.R              |  2 ++
 4 files changed, 14 insertions(+), 15 deletions(-)

diff --git a/.ci/download-r-revdeps.R b/.ci/download-r-revdeps.R
index 4317cd7e116b..a0339f02421b 100644
--- a/.ci/download-r-revdeps.R
+++ b/.ci/download-r-revdeps.R
@@ -17,7 +17,7 @@ reverse_deps <- depDF[["to"]]
 
 # skip some dependencies with known issues:
 #
-#   * 'misspi' ()
+#   * 'misspi' (https://github.com/microsoft/LightGBM/issues/6741)
 deps_to_skip <- "misspi"
 .log(sprintf("excluding %i reverse deps: %s", length(deps_to_skip), toString(deps_to_skip)))
 reverse_deps <- reverse_deps[!reverse_deps %in% deps_to_skip]
@@ -45,7 +45,7 @@ their_deps <- unlist(
 
 all_deps <- sort(unique(c(their_deps, reverse_deps)))
 
-# don't try to install 'lightgbm', or packages expected that ship with the R standard library
+# don't try to install 'lightgbm', or packages that ship with the R standard library
 all_deps <- all_deps[!all_deps %in% c("grid", "methods", "lightgbm", "parallel", "stats", "utils")]
 
 .log(sprintf("packages required to run these checks: %i", length(all_deps)))
diff --git a/.ci/run-revdep-checks.sh b/.ci/run-revdep-checks.sh
index 3146127ab732..b889b3e54c3f 100755
--- a/.ci/run-revdep-checks.sh
+++ b/.ci/run-revdep-checks.sh
@@ -4,12 +4,17 @@ set -e -u -o pipefail
 CHECKS_OUTPUT_DIR=/tmp/lgb-revdepchecks
 mkdir -p "${CHECKS_OUTPUT_DIR}"
 
-# pre-install all of lightgbm's reverse dependencies,
-# and all of their dependencies
+# Pre-install all of lightgbm's reverse dependencies, and all of their dependencies,
+# preferring precompiled binaries where available.
+#
+# This is done for speed... tools::check_packages_in_dir() only performs source
+# installs of all packages, which results in lots of compilation. {lightgbm} checks
+# do not need to care about that... as of this writing, nothing has {lightgbm} as a
+# 'LinkingTo' dependency or otherwise needs {lightgbm} at build time.
 Rscript ./.ci/download-r-revdeps.R "${CHECKS_OUTPUT_DIR}"
 
 # build and install 'lightgbm'
-sh build-cran-package.sh --no-build-vignettes
+sh ./build-cran-package.sh --no-build-vignettes
 R CMD INSTALL --with-keep.source ./lightgbm_*.tar.gz
 
 # run 'R CMD check' on lightgbm's reverse dependencies
diff --git a/.github/workflows/r_revdepchecks.yml b/.github/workflows/r_revdepchecks.yml
index b6f1532b2fcb..9e98f4745bce 100644
--- a/.github/workflows/r_revdepchecks.yml
+++ b/.github/workflows/r_revdepchecks.yml
@@ -19,10 +19,6 @@ env:
   # ignore R CMD CHECK NOTE checking how long it has
   # been since the last submission
   _R_CHECK_CRAN_INCOMING_REMOTE_: 0
-  # Indicate that no more than 2 threads should be used.
-  # ('misspi' explicitly read this variable, and expects it to be set to 'TRUE')
-  # ref: https://github.com/wch/r-source/blob/7feb54f6a71f1a6ec9e55ac0fb20115cd1a1d4e0/doc/manual/R-ints.texi#L4163
-  _R_CHECK_LIMIT_CORES_: 'TRUE'
   # CRAN ignores the "installed size is too large" NOTE,
   # so our CI can too. Setting to a large value here just
   # to catch extreme problems
@@ -38,6 +34,8 @@ jobs:
     timeout-minutes: 60
     strategy:
       fail-fast: false
+      # NOTE: platforms that CRAN provides pre-compiled binaries on (like macOS and Windows)
+      #       are preferable for this, because packages installs are much faster
       matrix:
         os:
           - macos-14
@@ -47,12 +45,6 @@ jobs:
           fetch-depth: 5
           submodules: true
       - uses: r-lib/actions/setup-pandoc@v2
-      - name: Install tinytex
-        if: startsWith(matrix.os, 'windows')
-        uses: r-lib/actions/setup-tinytex@v2
-        env:
-          CTAN_MIRROR: https://ctan.math.illinois.edu/systems/win32/miktex
-          TINYTEX_INSTALLER: TinyTeX
       - uses: r-lib/actions/setup-r@v2
         with:
           r-version: 'release'
diff --git a/R-package/R/lgb.train.R b/R-package/R/lgb.train.R
index 4d994cfc6f04..ef86143243cd 100644
--- a/R-package/R/lgb.train.R
+++ b/R-package/R/lgb.train.R
@@ -66,6 +66,8 @@ lgb.train <- function(params = list(),
                       reset_data = FALSE,
                       serializable = TRUE) {
 
+  stop("--- Intentional error for testing ---")
+
   # validate inputs early to avoid unnecessary computation
   if (nrounds <= 0L) {
     stop("nrounds should be greater than zero")