Update error messaging to bypass panicwrap only on non-recoverable

errors

While working on this change it was found that prefixing an error
message with the ErrorPrefix string would trigger a copyOutput function
that would copy any outputted string to Stderr, until a new ErrorPrefix
or Outprefix string is encountered in the output. During background runs of
Packer an error message with the ErrorPrefix was being outputted which
was causing all output, including Stdout, to be written to Stderr.

This change updates the logic to only override the Stdout logging
for non-recoverable errors. The idea being that any non-recoverable
error should bypass panicwrap so that user know an error occurred.
All other errors should follow the same behavior that we had prior to
Packer v1.7.1.

Closes #10855

main.go

@@ -152,6 +152,10 @@ func wrappedMain() int {
 	// passed into commands like `packer build`
 	config, err := loadConfig()
 	if err != nil {
+		// Writing to Stdout here so that the error message bypasses panicwrap. By using the
+		// ErrorPrefix this output will be redirected to Stderr by the copyOutput func.
+		// TODO: nywilken need to revisit this setup to better output errors to Stderr, and output to Stdout
+		// without panicwrap
 		fmt.Fprintf(os.Stdout, "%s Error loading configuration: \n\n%s\n", ErrorPrefix, err)
 		return 1
 	}
@@ -166,6 +170,10 @@ func wrappedMain() int {
 
 	cacheDir, err := packersdk.CachePath()
 	if err != nil {
+		// Writing to Stdout here so that the error message bypasses panicwrap. By using the
+		// ErrorPrefix this output will be redirected to Stderr by the copyOutput func.
+		// TODO: nywilken need to revisit this setup to better output errors to Stderr, and output to Stdout
+		// without panicwrap
 		fmt.Fprintf(os.Stdout, "%s Error preparing cache directory: \n\n%s\n", ErrorPrefix, err)
 		return 1
 	}
@@ -187,6 +195,7 @@ func wrappedMain() int {
 		// Set this so that we don't get colored output in our machine-
 		// readable UI.
 		if err := os.Setenv("PACKER_NO_COLOR", "1"); err != nil {
+			// Outputting error using Ui here to conform to the machine readable format.
 			ui.Error(fmt.Sprintf("Packer failed to initialize UI: %s\n", err))
 			return 1
 		}
@@ -202,12 +211,16 @@ func wrappedMain() int {
 			currentPID := os.Getpid()
 			backgrounded, err := checkProcess(currentPID)
 			if err != nil {
-				ui.Error(fmt.Sprintf("cannot determine if process is in background: %s\n", err))
+				// Writing to Stderr will ensure that the output gets captured by panicwrap.
+				// This error message and any other message writing to Stderr after this point will only show up with PACKER_LOG=1
+				// TODO: nywilken need to revisit this setup to better output errors to Stderr, and output to Stdout without panicwrap.
+				fmt.Fprintf(os.Stderr, "%s cannot determine if process is in background: %s\n", ErrorPrefix, err)
 			}
+
 			if backgrounded {
-				ui.Error("Running in background, not using a TTY\n")
+				fmt.Fprintf(os.Stderr, "%s Running in background, not using a TTY\n", ErrorPrefix)
 			} else if TTY, err := openTTY(); err != nil {
-				ui.Error(fmt.Sprintf("No tty available: %s\n", err))
+				fmt.Fprintf(os.Stderr, "%s No tty available: %s\n", ErrorPrefix, err)
 			} else {
 				basicUi.TTY = TTY
 				basicUi.PB = &packer.UiProgressBar{}
@@ -245,7 +258,11 @@ func wrappedMain() int {
 	}
 
 	if err != nil {
-		ui.Error(fmt.Sprintf("Error executing CLI: %s\n", err))
+		// Writing to Stdout here so that the error message bypasses panicwrap. By using the
+		// ErrorPrefix this output will be redirected to Stderr by the copyOutput func.
+		// TODO: nywilken need to revisit this setup to better output errors to Stderr, and output to Stdout
+		// without panicwrap
+		fmt.Fprintf(os.Stdout, "%s Error executing CLI: %s\n", ErrorPrefix, err)
 		return 1
 	}