Add [\!shouldfail] reproducer for transitive implicit-dep tracking bug

test/e2e/fixtures/header_dep_transitive/Tuprules.tup

@@ -0,0 +1,2 @@
+S = $(TUP_CWD)
+CFLAGS = -I$(S)/include

test/e2e/fixtures/header_dep_transitive/include/newhdr.h

@@ -0,0 +1,2 @@
+#pragma once
+#define EXTRA 100

test/e2e/fixtures/header_dep_transitive/include/old.h

@@ -0,0 +1,2 @@
+#pragma once
+#define ANSWER 1

test/e2e/fixtures/header_dep_transitive/src/Tupfile

@@ -0,0 +1,2 @@
+include_rules
+: main.c |> gcc $(CFLAGS) -c %f -o %o |> %B.o

test/e2e/fixtures/header_dep_transitive/src/main.c

@@ -0,0 +1,3 @@
+#include "old.h"
+int get_answer(void) { return ANSWER; }
+int main(void) { return get_answer(); }

test/e2e/fixtures/header_dep_transitive/test.sh

@@ -0,0 +1,122 @@
+#!/usr/bin/env bash
+# Reproducer for pup's transitive implicit-dep tracking bug.
+#
+# Scenario:
+#   1. Source includes only old.h. pup builds, records old.h as implicit dep.
+#   2. old.h is modified to transitively include a new header (newhdr.h).
+#      pup detects old.h changed and recompiles, but FAILS to add newhdr.h
+#      to the source's implicit-dep set.
+#   3. newhdr.h is modified. pup reports "Nothing to do." because its
+#      stale dep set says the source only depends on old.h (unchanged).
+#
+# Expected: step 3 rebuilds, .o reflects the new constant.
+# Observed: step 3 is a no-op; .o is stale.
+#
+# Test exits 0 on success (bug fixed), non-zero on failure (bug present).
+
+set -u
+
+PUP="${PUP:-$(command -v pup || echo /home/mural/bin/pup)}"
+BUILD_DIR="build/x86"
+OBJ="${BUILD_DIR}/src/main.o"
+
+die() {
+    echo "FAIL: $*" >&2
+    exit 1
+}
+
+# Extract the immediate-mode operand of the first mov $0xXX instruction.
+# Returns the hex literal as it appears in objdump output (e.g. "0x1").
+constant_in_obj() {
+    objdump -d "$1" 2>/dev/null \
+        | grep -oE 'mov +\$0x[0-9a-f]+' \
+        | head -1 \
+        | grep -oE '0x[0-9a-f]+'
+}
+
+# Decode a hex literal (with 0x prefix) to a decimal integer for printing.
+hex_to_dec() {
+    printf '%d' "$1" 2>/dev/null
+}
+
+# ---------- Step 1: initial build ----------
+echo "=== Step 1: initial build (source includes old.h only) ==="
+"$PUP" configure -B "$BUILD_DIR" >/dev/null || die "configure failed"
+"$PUP" -B "$BUILD_DIR" >/dev/null || die "initial build failed"
+[[ -f "$OBJ" ]] || die "expected $OBJ after initial build"
+
+K1="$(constant_in_obj "$OBJ")"
+echo "  observed constant in $OBJ: $K1 ($(hex_to_dec "$K1"))"
+[[ "$K1" == "0x1" ]] || die "expected 0x1 (ANSWER=1) after step 1, got $K1"
+
+# ---------- Step 2: make old.h transitively include newhdr.h ----------
+echo
+echo "=== Step 2: modify old.h to #include newhdr.h ==="
+cat > include/old.h << 'EOF'
+#pragma once
+#include "newhdr.h"
+#define ANSWER EXTRA
+EOF
+
+"$PUP" -B "$BUILD_DIR" >/dev/null || die "rebuild after old.h edit failed"
+
+K2="$(constant_in_obj "$OBJ")"
+echo "  observed constant in $OBJ: $K2 ($(hex_to_dec "$K2"))"
+[[ "$K2" == "0x64" ]] \
+    || die "expected 0x64 (EXTRA=100) after step 2, got $K2 — old.h change not picked up"
+
+# ---------- Forensic between step 2 and 3: did pup record newhdr.h? ----------
+# After step 2 the .d file from gcc lists both old.h AND newhdr.h. If pup's
+# dep-recording is healthy, both should appear as implicit edges for main.o's
+# compile. If newhdr.h is missing here, the bug is in dep recording (post-
+# execution .d-file processing), not in change detection.
+echo
+echo "=== Forensic: pup show index for main.c's compile after step 2 ==="
+INDEX_OUT="$("$PUP" show index -B "$BUILD_DIR" main.c 2>&1)"
+echo "$INDEX_OUT" | sed 's/^/  /'
+
+if echo "$INDEX_OUT" | grep -q "implicit:.*newhdr.h"; then
+    echo "  forensic: newhdr.h IS recorded as an implicit dep — proceed"
+else
+    echo
+    echo "  forensic: newhdr.h is NOT in main.c's implicit-dep set."
+    echo "            Root cause: pup's post-execution .d-file processing did"
+    echo "            not extend the implicit-dep set with newly-discovered"
+    echo "            transitive headers."
+fi
+
+# ---------- Step 3: modify newhdr.h (the transitive header) ----------
+echo
+echo "=== Step 3: modify newhdr.h (EXTRA 100 -> 7777) ==="
+cat > include/newhdr.h << 'EOF'
+#pragma once
+#define EXTRA 7777
+EOF
+
+OUT="$("$PUP" -B "$BUILD_DIR" 2>&1)"
+EC=$?
+echo "  pup output: $OUT"
+[[ $EC -eq 0 ]] || die "rebuild returned non-zero: $EC"
+
+K3="$(constant_in_obj "$OBJ")"
+echo "  observed constant in $OBJ: $K3 ($(hex_to_dec "$K3"))"
+
+if [[ "$OUT" == *"Nothing to do"* ]]; then
+    echo
+    echo "BUG PRESENT: pup reported 'Nothing to do' after newhdr.h change."
+    echo "             newhdr.h is transitively included by old.h, which is in"
+    echo "             the source's implicit-dep set, but newhdr.h itself was"
+    echo "             never recorded — confirmed by 'pup show index' above."
+fi
+
+if [[ "$K3" != "0x1e61" ]]; then
+    echo
+    echo "Diagnostic:"
+    echo "  expected $OBJ to contain 0x1e61 (EXTRA=7777)"
+    echo "  actually  contains $K3 ($(hex_to_dec "$K3"))"
+    echo "  this means main.c was NOT recompiled after newhdr.h changed"
+    die "transitive header change was not detected"
+fi
+
+echo
+echo "PASS: pup detected transitive header change."

test/unit/test_e2e.cpp

@@ -2105,6 +2105,29 @@ SCENARIO("Pupignore test via shell fixture", "[e2e][shell]")
     }
 }
 
+// Reproducer: when a source's already-tracked header is edited to transitively
+// include a new header, pup recompiles the source but fails to record the new
+// transitive header. Subsequent edits to that new header are then invisible to
+// change detection, and pup reports "Nothing to do" while the .o is stale.
+// See test/e2e/fixtures/header_dep_transitive/ and the parent project's
+// notes/pup-header-detection-bug.md.
+SCENARIO("Transitive implicit-dep header tracking", "[e2e][shell][incremental][!shouldfail]")
+{
+    WHEN("the header_dep_transitive shell fixture runs")
+    {
+        auto result = run_shell_fixture("header_dep_transitive");
+
+        THEN("a newly-transitive header's change triggers rebuild")
+        {
+            INFO("test.sh stdout:\n" << result.stdout_output);
+            INFO("test.sh stderr:\n" << result.stderr_output);
+            // CHECK (not REQUIRE) so !shouldfail can mark the case green
+            // without SIGABRT — the diagnostic output above survives.
+            CHECK(result.success());
+        }
+    }
+}
+
 // =============================================================================
 // Show Command Tests
 // =============================================================================