Fix initialization hook in the PROMPT_COMMAND array on Bash 5.1+

If PROMPT_COMMAND contains unrelated commands before installing
bash-preexec, then these unrelated commands may trigger
`__bp_preexec_invoke_exec`, which causes interactive mode marker to be
unset.  This causes preexec to be missed for the first interactive
command, since bash-preexec assumes that we are still not interactive.

Example of what can trigger such behavior: on Arch Linux in a login
shell /etc/profile.d/80-systemd-osc-context.sh causes
`__systemd_osc_context_precmdline` to be added to PROMPT_COMMAND, and
`__systemd_osc_context_precmdline` trips
`__bp_preexec_interactive_mode`.

This patch avoids the issue by appending our initialization hook as
the last element of PROMPT_COMMAND in Bash >= 5.1, instead of
appending the hook to the first element of PROMPT_COMMAND.

bash-preexec.sh

@@ -542,14 +542,18 @@ __bp_install_after_session_init() {
         __bp_require_not_readonly PS0 || return
     fi
 
-    local sanitized_prompt_command
-    __bp_sanitize_string sanitized_prompt_command "${PROMPT_COMMAND:-}"
-    if [[ -n "$sanitized_prompt_command" ]]; then
-        # shellcheck disable=SC2178 # PROMPT_COMMAND is not an array in bash <= 5.0
-        PROMPT_COMMAND=${sanitized_prompt_command}$'\n'
+    if __bp_use_array_prompt_command; then
+        PROMPT_COMMAND+=("${__bp_install_string}")
+    else
+        local sanitized_prompt_command
+        __bp_sanitize_string sanitized_prompt_command "${PROMPT_COMMAND:-}"
+        if [[ -n "$sanitized_prompt_command" ]]; then
+            # shellcheck disable=SC2178 # PROMPT_COMMAND is not an array in bash <= 5.0
+            PROMPT_COMMAND=${sanitized_prompt_command}$'\n'
+        fi
+        # shellcheck disable=SC2179 # PROMPT_COMMAND is not an array in bash <= 5.0
+        PROMPT_COMMAND+=${__bp_install_string}
     fi
-    # shellcheck disable=SC2179 # PROMPT_COMMAND is not an array in bash <= 5.0
-    PROMPT_COMMAND+=${__bp_install_string}
 }
 
 # Run our install so long as we're not delaying it.

test/bash-preexec.bats

@@ -76,13 +76,28 @@ set_exit_code_and_run_precmd() {
 
   # Assert that before running, the command contains the install string, and
   # afterwards it does not
-  [[ "$PROMPT_COMMAND" == *"$__bp_install_string"* ]] || return 1
+  [[ "$(join_PROMPT_COMMAND)" == *"$__bp_install_string"* ]] || return 1
 
   eval_PROMPT_COMMAND
 
-  [[ "$PROMPT_COMMAND" != *"$__bp_install_string"* ]] || return 1
+  [[ "$(join_PROMPT_COMMAND)" != *"$__bp_install_string"* ]] || return 1
 }
 
+@test "__bp_install should remove trap logic and itself from modified PROMPT_COMMAND" {
+  PROMPT_COMMAND=()
+  __bp_install_after_session_init
+  PROMPT_COMMAND="$PROMPT_COMMAND; true"
+
+  # Assert that before running, the command contains the install string, and
+  # afterwards it does not
+  [[ "$(join_PROMPT_COMMAND)" == *"$__bp_install_string"* ]] || return 1
+
+  eval_PROMPT_COMMAND
+
+  [[ "$(join_PROMPT_COMMAND)" != *"$__bp_install_string"* ]] || return 1
+}
+
+
 @test "__bp_install should preserve an existing DEBUG trap" {
   trap_invoked_count=0
   foo() { (( trap_invoked_count += 1 )); }
@@ -239,7 +254,9 @@ set_exit_code_and_run_precmd() {
 @test "Appending or prepending to PROMPT_COMMAND should work after bp_install_after_session_init" {
     __bp_install_after_session_init
     nl=$'\n'
-    PROMPT_COMMAND="$PROMPT_COMMAND; true"
+    # On Bash 5.1+ we append to the array properly,
+    # so first element of PROMPT_COMMAND may still be empty.
+    PROMPT_COMMAND="${PROMPT_COMMAND:+$PROMPT_COMMAND; }true"
     PROMPT_COMMAND="$PROMPT_COMMAND $nl true"
     PROMPT_COMMAND="$PROMPT_COMMAND; true"
     PROMPT_COMMAND="true; $PROMPT_COMMAND"
@@ -249,6 +266,24 @@ set_exit_code_and_run_precmd() {
     eval_PROMPT_COMMAND
 }
 
+@test "Appending or prepending to PROMPT_COMMAND array should work after bp_install_after_session_init" {
+    if __bp_use_array_prompt_command; then
+        PROMPT_COMMAND=()
+        __bp_install_after_session_init
+        nl=$'\n'
+        PROMPT_COMMAND=("${PROMPT_COMMAND[@]}" "true")
+        PROMPT_COMMAND=("${PROMPT_COMMAND[@]}" "$nl true")
+        PROMPT_COMMAND=("${PROMPT_COMMAND[@]}" "true")
+        PROMPT_COMMAND=("true" "${PROMPT_COMMAND[@]}")
+        PROMPT_COMMAND=("true" "${PROMPT_COMMAND[@]}")
+        PROMPT_COMMAND=("true" "${PROMPT_COMMAND[@]}")
+        PROMPT_COMMAND=("true $nl" "${PROMPT_COMMAND[@]}")
+        eval_PROMPT_COMMAND
+    else
+        skip
+    fi
+}
+
 # Case where a user is appending or prepending to PROMPT_COMMAND.
 # This can happen after 'source bash-preexec.sh' e.g.
 # source bash-preexec.sh; PROMPT_COMMAND="$PROMPT_COMMAND; other_prompt_command_hook"
@@ -268,7 +303,11 @@ set_exit_code_and_run_precmd() {
 @test "Adding to PROMPT_COMMAND after with semicolon" {
     PROMPT_COMMAND="echo before"
     __bp_install_after_session_init
-    PROMPT_COMMAND="$PROMPT_COMMAND; echo after"
+    if __bp_use_array_prompt_command; then
+        PROMPT_COMMAND[${#PROMPT_COMMAND[@]}-1]+='; echo after'
+    else
+        PROMPT_COMMAND+='; echo after'
+    fi
 
     eval_PROMPT_COMMAND
 
@@ -285,12 +324,38 @@ set_exit_code_and_run_precmd() {
 
     precmd() { echo "inside precmd"; }
     run eval_PROMPT_COMMAND
+    [ "${#lines[@]}" == '5' ]
     [ "${lines[0]}" == "after2" ]
     [ "${lines[1]}" == "before" ]
     [ "${lines[2]}" == "before2" ]
-    [ "${lines[3]}" == "inside precmd" ]
-    [ "${lines[4]}" == "after" ]
-    [ "${#lines[@]}" == '5' ]
+    if __bp_use_array_prompt_command; then
+        [ "${lines[3]}" == "after" ]
+        [ "${lines[4]}" == "inside precmd" ]
+    else
+        [ "${lines[3]}" == "inside precmd" ]
+        [ "${lines[4]}" == "after" ]
+    fi
+}
+
+@test "during install PROMPT_COMMAND and precmd functions should be executed each once (Bash 5.1+ PROMPT_COMMAND array)" {
+    if __bp_use_array_prompt_command; then
+        PROMPT_COMMAND=("echo before")
+        PROMPT_COMMAND=("${PROMPT_COMMAND[@]}" "echo before2")
+        __bp_install_after_session_init
+        PROMPT_COMMAND=("${PROMPT_COMMAND[@]}" "echo after")
+        PROMPT_COMMAND=("echo after2" "${PROMPT_COMMAND[@]}")
+
+        precmd() { echo "inside precmd"; }
+        run eval_PROMPT_COMMAND
+        [ "${#lines[@]}" == '5' ]
+        [ "${lines[0]}" == "after2" ]
+        [ "${lines[1]}" == "before" ]
+        [ "${lines[2]}" == "before2" ]
+        [ "${lines[3]}" == "inside precmd" ]
+        [ "${lines[4]}" == "after" ]
+    else
+        skip
+    fi
 }
 
 @test "No functions defined for preexec should simply return" {