Add check-pr script

This script will be run by Travis-CI (on PR builds only) to run some useful
checks. Refer to the comment at the top of the script for more information.

scripts/check-pr.sh

@@ -0,0 +1,119 @@
+#!/usr/bin/env bash
+
+# This script is executed by Travis CI for every pull request opened.
+# It currently accomplishes the following objectives (for English pages only):
+#
+#  1. Detect pages that were just copied (i.e. cp pages/{common,linux}/7z.md).
+#  2. Detect pages that were added in a platform specific directory although
+#     they already exist under 'common'.
+#  3. Detect pages that were added in the 'common' platform although they
+#     already exist under a platform specific directory.
+#  4. Detect other miscellaneous anomalies in the pages folder.
+#
+# Results are printed to stdout, logs and errors to stderr.
+#
+# NOTE: must be run from the repository root directory to correctly work!
+# NOTE: no `set -e`, failure of this script should not invalidate the build.
+
+# Check for duplicated pages.
+function check_duplicates {
+  local msg='The page `%s` already exists under the `%s` platform.\n'
+  local page=$1 # page path in the format 'platform/pagename.md'
+  local parts
+  local other
+
+  readarray -td'/' parts < <(echo -n "$page")
+
+  local platform=${parts[0]}
+  local file=${parts[1]}
+
+  case "$platform" in
+    common) # check if page already exists in other platforms
+      for other in `ls pages/`; do
+        if [ "$other" != 'common' ]; then
+          if [ -f "pages/$other/$file" ]; then
+            printf "\x2d $msg" "$page" "$other"
+          fi
+        fi
+      done
+      ;;
+
+    *) # check if page already exists under common
+      if [ -f "pages/common/$file" ]; then
+        printf "\x2d $msg" "$page" 'common'
+      fi
+      ;;
+  esac
+}
+
+# Look at git diff and check for copied/duplicated pages.
+function check_diff {
+  local msg='The page `%s` seems to be a copy of `%s` (%d%% matching).\n'
+  local git_diff
+  local line
+  local entry
+
+  git_diff=`git diff --name-status --find-copies-harder --diff-filter=AC --relative=pages/ master`
+
+  if [ -n "$git_diff" ]; then
+    echo -e "Check PR: git diff:\n$git_diff" >&2
+  else
+    echo 'Check PR: looks fine, no interesting changes detected.' >&2
+    return 0
+  fi
+
+  while read line; do
+    readarray -td$'\t' entry < <(echo -n "$line")
+
+    local change="${entry[0]}"
+    local file1="${entry[1]}"
+    local file2="${entry[2]}"
+
+    case "$change" in
+      C*) # file2 is a copy of file1
+        local percentage=${change#C}
+        percentage=${percentage#0}
+        percentage=${percentage#0}
+
+        printf "\x2d $msg" "$file2" "$file1" "$percentage"
+        ;;
+
+      A) # file1 was newly added
+        check_duplicates "$file1"
+        ;;
+    esac
+  done <<< "$git_diff"
+}
+
+# Recursively check the pages/ folder for anomalies.
+function check_structure {
+  local msg_not_dir='The file `%s` does not look like a directory.\n'
+  local msg_not_file='The file `%s` does not look like a regular file.\n'
+  local msg_not_md='The file `%s` does not have a `.md` extension.\n'
+
+  for platform in pages/*; do
+    if [ ! -d "$platform" ]; then
+      printf "\x2d $msg_not_dir" "$platform"
+    else
+      for page in "$platform"/*; do
+        if [ ! -f "$page" ]; then
+          printf "\x2d $msg_not_file" "$page"
+        elif [ "${page:(-3)}" != ".md" ]; then
+          printf "\x2d $msg_not_md" "$page"
+        fi
+      done
+    fi
+  done
+}
+
+###################################
+# MAIN
+###################################
+
+if [ "$TRAVIS" = "true" ] && [ "$TRAVIS_REPO_SLUG" = "tldr-pages/tldr" ] && [ "$TRAVIS_PULL_REQUEST" != "false" ]; then
+  check_diff
+  check_structure
+else
+  echo 'Not a pull request, refusing to run.' >&2
+  exit 0
+fi