Keep the end of long output, and pass the command line to _helpless

etc/profile.d/help50.sh

@@ -53,8 +53,15 @@ function _help50() {
         # Remove script's own output (if this is user's first command)
         typescript=$(echo "$typescript" | sed '1{/^Script started on .*/d}')
 
-        # Cap typescript at MIN(1K lines, 1M bytes), else `read` is slow
-        typescript=$(echo "$typescript" | head -n 1024 | cut -b 1-1048576)
+        # Cap typescript, else `read` below is slow. Keep the first few lines, where the
+        # command line itself is echoed (found below), plus the last 1K lines, where
+        # errors tend to be (tracebacks, `make: *** Error`, segfaults); a long-running
+        # program that prints a lot and then crashes would otherwise lose its error.
+        typescript=$(echo "$typescript" | cut -b 1-1048576)
+        local total=$(echo "$typescript" | wc -l)
+        if [[ $total -gt 1088 ]]; then
+            typescript=$(echo "$typescript" | head -n 64; echo "[... $((total - 1088)) lines omitted ...]"; echo "$typescript" | tail -n 1024)
+        fi
 
         # Remove ANSI characters
         typescript=$(echo "$typescript" | ansi2txt)
@@ -108,8 +115,10 @@ function _help50() {
             _helpful "$help"
         elif [[ $status -ne 0 ]]; then # If helpless
 
-            # Cap what's relayed downstream (e.g., ddb50 rejects > 10,000 characters), keeping the end, where errors tend to be
-            _helpless "$(echo "$typescript" | tail -c 8192)"
+            # Pass the output (capped, e.g., since ddb50 rejects > 10,000 characters, keeping the end,
+            # where errors tend to be) and the command line itself, so that whatever explains the
+            # output can see what was run
+            _helpless "$(echo "$typescript" | tail -c 8192)" "$argv"
         fi
     else
         _helped
@@ -123,7 +132,11 @@ function _rhetorical() {
     _alert "That was a rhetorical question. <3"
 }
 
-# Default helpers
+# Default helpers, overridable (e.g., by cs50/codespace) by defining them before this file is sourced:
+#   _helped              last command succeeded
+#   _helpful ADVICE      a helper had advice for the failed command
+#   _helpless OUTPUT CMD no helper had advice; OUTPUT is the failed command's (cleaned, capped)
+#                        output, possibly empty, and CMD its command line
 if ! type _helped >/dev/null 2>&1; then
     function _helped() { :; } # Silent
 fi

tests/smoke.sh

@@ -25,4 +25,27 @@ run "$IMAGE" bash --login -c 'valgrind python x.py < /dev/null; test $? -eq 1' 2
 echo "- _fold wraps without a terminal"
 run "$IMAGE" bash --login -c '. /opt/cs50/lib/cli; TERM= _fold "$(printf "a %.0s" {1..100})"' | head -n 1 | grep -qE '^.{1,80}$'
 
+echo "- _helpless gets the end of a failed command's long output, plus its command line"
+run "$IMAGE" bash --login -c '
+    export HELP50=$(mktemp)
+    _helpless() { printf "%s" "$1" > /tmp/output; printf "%s" "$2" > /tmp/cmd; }
+    . /etc/profile.d/help50.sh
+
+    # A command that prints 3000 lines and then fails, as script(1) records it
+    { printf "$ ./slow\r\n"; seq 3000 | sed "s/$/\r/"; printf "Error: boom\r\n"; } > "$HELP50"
+    set -o history; history -s ./slow; set +o history
+    false; _help50
+    test "$(cat /tmp/cmd)" = ./slow &&
+    test "$(head -n 1 /tmp/output)" = 1 &&
+    grep -qx "\[... 1914 lines omitted ...\]" /tmp/output &&
+    ! grep -qx 1000 /tmp/output &&
+    test "$(tail -n 1 /tmp/output)" = "Error: boom" || exit 1
+
+    # A command that fails without output
+    : > "$HELP50"
+    set -o history; history -s ./slow; set +o history
+    false; _help50
+    test "$(cat /tmp/cmd)" = ./slow && test ! -s /tmp/output || exit 1
+'
+
 echo "OK"