compiler: handle a panic when an error is produced, but source == ''

vlib/v/util/errors.v

@@ -13,24 +13,24 @@ import v.token
 // NB: using only the filename may lead to inability of IDE/editors
 // to find the source file, when the IDE has a different working folder than
 // v itself.
-
+// error_context_before - how many lines of source context to print before the pointer line
+// error_context_after - ^^^ same, but after
 const (
-	error_context_before = 2 // how many lines of source context to print before the pointer line
+	error_context_before = 2
-	error_context_after = 2 // ^^^ same, but after
+	error_context_after  = 2
 )
 
+// emanager.support_color - should the error and other messages
+// have ANSI terminal escape color codes in them.
+// By default, v tries to autodetect, if the terminal supports colors.
+// Use -color and -nocolor options to override the detection decision.
 pub const (
 	emanager = new_error_manager()
 )
 
-//
-
 pub struct EManager {
 pub mut:
-	support_color bool // should the error and other messages
+	support_color bool
-	// have ANSI terminal escape color codes in them.
-	// By default, v tries to autodetect, if the terminal supports colors.
-	// Use -color and -nocolor options to override the detection decision.
 }
 
 pub fn (e &EManager) set_support_color(b bool) {
@@ -38,10 +38,13 @@ pub fn (e &EManager) set_support_color(b bool) {
 }
 
 pub fn new_error_manager() &EManager {
-	return &EManager{ support_color: term.can_show_color_on_stderr() }
+	return &EManager{
+		support_color: term.can_show_color_on_stderr()
+	}
 }
 
-pub fn formatted_error(kind string /*error or warn*/, emsg string, filepath string, pos token.Position) string {
+// formatted_error - `kind` may be 'error' or 'warn'
+pub fn formatted_error(kind, emsg, filepath string, pos token.Position) string {
 	mut path := filepath
 	verror_paths_override := os.getenv('VERROR_PATHS')
 	if verror_paths_override == 'absolute' {
@@ -55,20 +58,43 @@ pub fn formatted_error(kind string /*error or warn*/, emsg string, filepath stri
 	}
 	//
 	mut source_context := ''
-	source := util.read_file(filepath) or { '' }
+	source := read_file(filepath) or {
-	source_lines := source.split_into_lines()
+		''
-	mut p := util.imax(0, util.imin(source.len -1, pos.pos))
+	}
+	mut p := imax(0, imin(source.len - 1, pos.pos))
+	if source.len > 0 {
 		for ; p >= 0; p-- {
 			if source[p] == `\r` || source[p] == `\n` {
 				break
 			}
 		}
-	column := util.imax(0, pos.pos - p - 1)
+	}
+	column := imax(0, pos.pos - p - 1)
 	position := '${path}:${pos.line_nr+1}:${util.imax(1,column+1)}:'
+	source_context += source_context(source, column, pos).join('\n')
+	final_position := if emanager.support_color { term.bold(position) } else { position }
+	mut final_kind := kind
+	if emanager.support_color {
+		final_kind = if kind.contains('error') {
+			term.bold(term.red(kind))
+		} else {
+			term.bold(term.bright_blue(kind))
+		}
+	}
+	final_msg := emsg // if emanager.support_color { term.bold(emsg) } else { emsg }
+	final_context := if source_context.len > 0 { '\n$source_context' } else { '' }
 	//
-	bline := util.imax(0, pos.line_nr - error_context_before)
+	return '$final_position $final_kind $final_msg $final_context'.trim_space()
-	aline := util.imin(source_lines.len-1, pos.line_nr + error_context_after)
+}
+
+pub fn source_context(source string, column int, pos token.Position) []string {
 	mut clines := []string{}
+	if source.len == 0 {
+		return clines
+	}
+	source_lines := source.split_into_lines()
+	bline := imax(0, pos.line_nr - error_context_before)
+	aline := imax(0, imin(source_lines.len - 1, pos.line_nr + error_context_after))
 	tab_spaces := '    '
 	for iline := bline; iline <= aline; iline++ {
 		sline := source_lines[iline]
@@ -84,13 +110,17 @@ pub fn formatted_error(kind string /*error or warn*/, emsg string, filepath stri
 			// where it is needed. That is the reason we can not just
 			// use strings.repeat(` `, col) to form it.
 			mut pointerline := []string{}
-			for i, c in sline {
+			for i, bchar in sline {
 				if i < column {
-					mut x := c
+					mut x := bchar
 					if x == `\t` {
 						pointerline << tab_spaces
 					} else {
-						x = if x.is_space() { c } else { ` ` }
+						x = if x.is_space() {
+							bchar
+						} else {
+							` `
+						}
 						pointerline << x.str()
 					}
 					continue
@@ -99,37 +129,27 @@ pub fn formatted_error(kind string /*error or warn*/, emsg string, filepath stri
 					max_len := sline.len - pointerline.len // rest of the line
 					len := if pos.len > max_len { max_len } else { pos.len }
 					underline := '~'.repeat(len)
-					pointerline << if emanager.support_color { term.bold(term.blue(underline)) } else { underline }
+					pointerline << if emanager.support_color {
+						term.bold(term.blue(underline))
 					} else {
-					pointerline << if emanager.support_color { term.bold(term.blue('^')) } else { '^' }
+						underline
+					}
+				} else {
+					pointerline << if emanager.support_color {
+						term.bold(term.blue('^'))
+					} else {
+						'^'
+					}
 				}
 				break
 			}
 			clines << '       ' + pointerline.join('')
 		}
 	}
-	source_context += clines.join('\n')
+	return clines
-	//
-	final_position := if emanager.support_color {
-		term.bold(position)
-	} else {
-		position
-	}
-	mut final_kind := kind
-	if emanager.support_color {
-		final_kind = if kind.contains('error') {
-			term.bold(term.red(kind))
-		}else{
-			term.bold(term.bright_blue(kind))
-		}
-	}
-	final_msg := emsg // if emanager.support_color { term.bold(emsg) } else { emsg }
-	final_context := if source_context.len > 0 { '\n$source_context' } else { '' }
-	//
-	return '$final_position $final_kind $final_msg $final_context'.trim_space()
 }
 
-pub fn verror(kind string, s string) {
+pub fn verror(kind, s string) {
 	if emanager.support_color {
 		eprintln(term.bold(term.red(kind)) + ': $s')
 	} else {