command/format: Don't try to fill the last terminal column

In some terminal emulators, writing a character into the last column on a
row causes the terminal to immediately wrap to the beginning of the next
line, even if the very next character in the stream is a hard newline.
That can then lead to errant blank lines in the final output which make
it harder to navigate the visual hierarchy.

As a compromise to avoid this, we'll format our horizontal rules and
paragraphs to one column less than the terminal width. That does mean that
our horizontal rules won't _quite_ cover the whole terminal width, but
it seems like a good compromise in order to get consistent behavior across
a wider variety of terminal implementations.

command/format/diagnostic.go

@@ -183,11 +183,11 @@ func Diagnostic(diag tfdiags.Diagnostic, sources map[string][]byte, color *color
 	}
 
 	if desc.Detail != "" {
-		if width != 0 {
+		if width > 1 {
 			lines := strings.Split(desc.Detail, "\n")
 			for _, line := range lines {
 				if !strings.HasPrefix(line, " ") {
-					line = wordwrap.WrapString(line, uint(width))
+					line = wordwrap.WrapString(line, uint(width-1))
 				}
 				fmt.Fprintf(&buf, "%s\n", line)
 			}

command/format/diagnostic_test.go

@@ -403,8 +403,8 @@ wrap onto multiple lines. Thank-you very much for listening.
 To fix this, run this very long command:
   terraform read-my-mind -please -thanks -but-do-not-wrap-this-line-because-it-is-prefixed-with-spaces
 
-Here is a coda which is also long enough to wrap and so it should eventually
-make it onto multiple lines. THE END
+Here is a coda which is also long enough to wrap and so it should
+eventually make it onto multiple lines. THE END
 `
 	output := Diagnostic(diags[0], nil, color, 76)
 

command/format/trivia.go

@@ -16,7 +16,10 @@ import (
 // This is intended for printing to the UI via mitchellh/cli.UI.Output, or
 // similar, which will automatically append a trailing newline too.
 func HorizontalRule(color *colorstring.Colorize, width int) string {
-	rule := strings.Repeat("─", width)
+	if width <= 1 {
+		return "\n"
+	}
+	rule := strings.Repeat("─", width-1)
 	if color == nil { // sometimes unit tests don't populate this properly
 		return "\n" + rule
 	}
@@ -34,7 +37,7 @@ func HorizontalRule(color *colorstring.Colorize, width int) string {
 // unbroken. This allows including literal segments in the output, such as
 // code snippets or filenames, where word wrapping would be confusing.
 func WordWrap(str string, width int) string {
-	if width == 0 {
+	if width <= 1 {
 		// Silly edge case. We'll just return the original string to avoid
 		// panicking or doing other weird stuff.
 		return str
@@ -44,7 +47,7 @@ func WordWrap(str string, width int) string {
 	lines := strings.Split(str, "\n")
 	for i, line := range lines {
 		if !strings.HasPrefix(line, " ") {
-			line = wordwrap.WrapString(line, uint(width))
+			line = wordwrap.WrapString(line, uint(width-1))
 		}
 		if i > 0 {
 			buf.WriteByte('\n') // reintroduce the newlines we skipped in Scan

command/state_mv_test.go

@@ -503,7 +503,8 @@ func TestStateMv_differentResourceTypes(t *testing.T) {
 		t.Fatalf("expected error output, got:\n%s", ui.OutputWriter.String())
 	}
 
-	if !strings.Contains(ui.ErrorWriter.String(), "resource types don't match") {
+	errOutput := strings.Replace(ui.ErrorWriter.String(), "\n", " ", -1)
+	if !strings.Contains(errOutput, "resource types don't match") {
 		t.Fatalf("expected initialization error, got:\n%s", ui.ErrorWriter.String())
 	}
 }