Support interactive issue resolution prompts

This adds a new flag, -i / --interactive, which enables opening a
Bash prompt whenever something goes wrong in the bootstrap. This is
highly useful when developing or debugging live-bootstrap, but it
needs to be off by default, for use in automated processes.

In the future, asking for variables at runtime could (and perhaps
should) also be gated behind this flag.

rootfs.py

@@ -32,6 +32,7 @@ def create_configuration_file(args):
         config.write(f"UPDATE_CHECKSUMS={args.update_checksums}\n")
         config.write(f"JOBS={args.cores}\n")
         config.write(f"INTERNAL_CI={args.internal_ci or False}\n")
+        config.write(f"INTERACTIVE={args.interactive}\n")}
         config.write(f"BARE_METAL={args.bare_metal}\n")
         if (args.bare_metal or args.qemu) and not args.kernel:
             if args.repo or args.external_sources:
@@ -70,21 +71,24 @@ def main():
                         help="Force all files timestamps to be 0 unix time",
                         action="store_true")
     parser.add_argument("--update-checksums",
-                        help="Update checksum files.",
+                        help="Update checksum files",
                         action="store_true")
     parser.add_argument("--external-sources",
-                        help="Download sources externally from live-bootstrap.",
+                        help="Download sources externally from live-bootstrap",
                         action="store_true")
     parser.add_argument("--build-kernels",
-                        help="Also build kernels in chroot and bwrap builds.",
+                        help="Also build kernels in chroot and bwrap builds",
                         action="store_true")
     parser.add_argument("--no-create-config",
                         help="Do not automatically create config file",
                         action="store_true")
+    parser.add_argument("-i", "--interactive",
+                        help="Use interactive prompts to resolve issues during bootstrap",
+                        action="store_true")
     parser.add_argument("-r", "--repo",
-                        help="Path to prebuilt binary packages.", nargs=None)
+                        help="Path to prebuilt binary packages", nargs=None)
     parser.add_argument("--early-preseed",
-                        help="Skip early stages of live-bootstrap.", nargs=None)
+                        help="Skip early stages of live-bootstrap", nargs=None)
     parser.add_argument("--internal-ci", help="INTERNAL for github CI")
 
     # QEMU arguments

seed/script-generator.c

@@ -425,7 +425,17 @@ FILE *start_script(int id, int using_bash) {
 
 	if (using_bash) {
 		fputs("#!/bin/bash\n", out);
-		fputs("set -e\n", out);
+		if (strcmp(get_var("INTERACTIVE"), "True") == 0) {
+			if (using_bash != 1) {
+				fputs("trap 'env PS1=\"[TRAP] \\w # \" bash -i' ERR\n", out);
+			} else {
+				fputs("trap 'bash -c '\"'\"'while true; do printf \""
+				"[TRAP - use Ctrl+D] $(pwd) # \"; $(cat); done'\"'\"'' ERR\n",
+				out);
+			}
+		} else {
+			fputs("set -e\n", out);
+		}
 		fputs("cd /steps\n", out);
 		fputs(". ./bootstrap.cfg\n", out);
 		fputs(". ./env\n", out);
@@ -537,7 +547,7 @@ void generate(Directive *directives) {
 					 */
 					generate_preseed_jump(counter);
 				}
-				using_bash = 1;
+				using_bash += 1;
 				/* Create call to new script. */
 				output_call_script(out, "", int2str(counter, 10, 0), using_bash, 0);
 				fclose(out);