portindex: Do not exit non-zero on failed ports

The change in 217d852 broke existing use cases, including the portindex
run in mportsync. Restore the previous behavior by default and only exit
with a non-zero exit code if requested with the new flag 'portindex -e'.

See: #64

src/port/portindex.tcl

@@ -8,6 +8,7 @@ package require Pextlib
 
 # Globals
 set full_reindex 0
+set permit_error 0
 set stats(total) 0
 set stats(failed) 0
 set stats(skipped) 0
@@ -22,9 +23,10 @@ mportinit ui_options global_options global_variations
 # Standard procedures
 proc print_usage args {
     global argv0
-    puts "Usage: $argv0 \[-df\] \[-o output directory\] \[-p plat_ver_arch\] \[directory\]"
+    puts "Usage: $argv0 \[-dfe\] \[-o output directory\] \[-p plat_ver_arch\] \[directory\]"
     puts "-d:\tOutput debugging information"
     puts "-f:\tDo a full re-index instead of updating"
+    puts "-e:\tExit code indicates if ports failed to parse"
     puts "-o:\tOutput all files to specified directory"
     puts "-p:\tPretend to be on another platform"
 }
@@ -205,6 +207,8 @@ for {set i 0} {$i < $argc} {incr i} {
                 lappend port_options os.platform $os_platform os.major $os_major os.arch $os_arch
             } elseif {$arg eq "-f"} { # Completely rebuild index
                 set full_reindex 1
+            } elseif {$arg eq "-e"} { # Non-zero exit code on errors
+                set permit_error 1
             } else {
                 puts stderr "Unknown option: $arg"
                 print_usage
@@ -301,6 +305,6 @@ puts "\nTotal number of ports parsed:\t$stats(total)\
       \nPorts failed:\t\t\t$stats(failed)\
       \nUp-to-date ports skipped:\t$stats(skipped)\n"
 
-if {$stats(failed) > 0} {
+if {${permit_error} && $stats(failed) > 0} {
     exit 1
 }