From 51bf3da97791dfdcaa80015c419dcf4a39055733 Mon Sep 17 00:00:00 2001
From: Raphael Speyer <raphael.speyer@digitalasset.com>
Date: Fri, 8 Dec 2023 18:35:54 +1100
Subject: [PATCH] precommit: add check for modified files under packages with
 `main-only` targets. (#17993)

Since https://github.com/digital-asset/daml/pull/17989

A simple heuristic to remind you to consider adding `run-all-tests: true` to your commit message if making changes in corners of the codebase most likely affected.
---
 .pre-commit-config.yaml                |  7 ++++++
 dev-env/bin/dade-check-main-only-files | 30 ++++++++++++++++++++++++++
 2 files changed, 37 insertions(+)
 create mode 100755 dev-env/bin/dade-check-main-only-files

diff --git a/.pre-commit-config.yaml b/.pre-commit-config.yaml
index 8c4d63853979..034eafc225d1 100644
--- a/.pre-commit-config.yaml
+++ b/.pre-commit-config.yaml
@@ -51,3 +51,10 @@ repos:
       language: system
       pass_filenames: false
       entry: "pre-commit/platform-independence-check.sh"
+    - id: mainonly
+      name: main only
+      description: Check for changes under packages with targets tagged with main-only
+      language: system
+      pass_filenames: true
+      entry: "dade-check-main-only-files"
+      types: [text]
diff --git a/dev-env/bin/dade-check-main-only-files b/dev-env/bin/dade-check-main-only-files
new file mode 100755
index 000000000000..d106a10d4aff
--- /dev/null
+++ b/dev-env/bin/dade-check-main-only-files
@@ -0,0 +1,30 @@
+#!/usr/bin/env bash
+#
+# Checks whether any of the modified files sit under packages with targets marked as 'main-only'.
+#
+# This is as intended a simple heuristic to avoid accidentally omitting 'run-all-tests: true'
+# on a PR branch which touches those files.
+#
+
+DADE_SKIP_MAIN_ONLY_CHECK="${DADE_SKIP_MAIN_ONLY_CHECK:-$(git log -1 --format=%b | tr -d ' ' | grep '^run-all-tests:true$')}"
+if [[ -n "$DADE_SKIP_MAIN_ONLY_CHECK" ]]; then
+  # The user has been explicit about whether they want all tests run,
+  # either by setting the env var, or adding a line to their last commit.
+  exit 0; 
+fi
+
+MODIFIED_FILES=$(echo "$@" | xargs -n1 | sort)
+MAIN_ONLY_DIRS=$(bazel query "attr(tags, 'main-only', //...)" 2>/dev/null | awk -F: '{print $1}' | sort -u | sed -e 's|^//||')
+
+# Does a cartesian product of the main-only dirs and modified files, and filters to files that are within dir.
+SUSPECT_FILES=$(join -j99 <(echo "$MAIN_ONLY_DIRS") <(echo "$MODIFIED_FILES") | awk '$1 == substr($2, 1, length($1)) {print $2}')
+
+if [[ -n "$SUSPECT_FILES" ]]; then
+  echo "
+The following modified files sit under a directory with 'main-only' targets:
+$SUSPECT_FILES
+
+Consider putting a line with 'run-all-tests: true' in your PR description, or \`export DADE_SKIP_MAIN_ONLY_CHECK=1\` and try again.
+    " >&2
+  exit 1
+fi