From 7a99949f0ea82d9d4cf537b2d5dd52f0c3b53652 Mon Sep 17 00:00:00 2001
From: Delyan Angelov <delian66@gmail.com>
Date: Mon, 6 Apr 2020 19:39:58 +0300
Subject: [PATCH] errors: print more informative and pretty errors

---
 vlib/v/scanner/scanner.v | 13 ++--------
 vlib/v/util/errors.v     | 53 ++++++++++++++++++++++++++++++++++++----
 vlib/v/util/util.v       | 16 ++++++++++++
 3 files changed, 66 insertions(+), 16 deletions(-)

diff --git a/vlib/v/scanner/scanner.v b/vlib/v/scanner/scanner.v
index 351658a613..ced523ccf4 100644
--- a/vlib/v/scanner/scanner.v
+++ b/vlib/v/scanner/scanner.v
@@ -55,19 +55,10 @@ pub fn new_scanner_file(file_path string, comments_mode CommentsMode) &Scanner {
 	if !os.exists(file_path) {
 		verror("$file_path doesn't exist")
 	}
-	mut raw_text := os.read_file(file_path) or {
-		verror('scanner: failed to open $file_path')
+	raw_text := util.read_file( file_path ) or {
+		verror(err)
 		return 0
 	}
-	// BOM check
-	if raw_text.len >= 3 {
-		c_text := raw_text.str
-		if c_text[0] == 0xEF && c_text[1] == 0xBB && c_text[2] == 0xBF {
-			// skip three BOM bytes
-			offset_from_begin := 3
-			raw_text = tos(c_text[offset_from_begin], vstrlen(c_text) - offset_from_begin)
-		}
-	}
 	mut s := new_scanner(raw_text, comments_mode) // .skip_comments)
 	// s.init_fmt()
 	s.file_path = file_path
diff --git a/vlib/v/util/errors.v b/vlib/v/util/errors.v
index 05601587be..da73571a79 100644
--- a/vlib/v/util/errors.v
+++ b/vlib/v/util/errors.v
@@ -53,13 +53,56 @@ pub fn formated_error(kind string /*error or warn*/, emsg string, filepath strin
 			path = path.replace(workdir, '')
 		}
 	}
-	column := 0
-	position := '${path}:${pos.line_nr+1}:$column:'
-	// QTODO: retrieve source lines around pos.line_nr and add them here
+	//
+	mut column := 0
 	mut source_context := ''
+	source := util.read_file(filepath) or { '' }
+	source_lines := source.split_into_lines()
+	if source.len > pos.pos {
+		mut p := pos.pos
+		for ; p>=0; p-- {
+			if source[p] == `\r` || source[p] == `\n` {
+				break
+			}
+		}
+		column = pos.pos - p
+	}
+	position := '${path}:${pos.line_nr+1}:$column:'
+	//
+	bline := pos.line_nr - error_context_before
+	aline := pos.line_nr + error_context_after
+	mut clines := []string
+	for iline, sline in source_lines {
+		if iline >= bline && iline <= aline {
+			mut cline := '${iline+1:5d}| $sline'
+			if iline == pos.line_nr && emanager.support_color {
+				cline = term.red( cline )
+			}
+			clines << cline
+			//
+			if iline == pos.line_nr {
+				// The pointerline should have the same spaces/tabs as the offending
+				// line, so that it prints the ^ character exactly on the *same spot*
+				// where it is needed. That is the reason we can not just
+				// use strings.repeat(` `, col) to form it.
+				mut pointerline := []string
+				for i, c in cline {
+					if i < column {
+						x := if c.is_space() { c } else { ` ` }
+						pointerline << x.str()
+						continue
+					}
+					pointerline << if emanager.support_color { term.bold(term.blue('^')) } else { '^' }
+					break
+				}
+				clines << '      ' + pointerline.join('')
+			}
+		}
+	}
+	source_context += clines.join('\n')
 	//
 	final_position := if emanager.support_color {
-		term.bold(position) // term.white(position))
+		term.bold(position)
 	} else {
 		position
 	}
@@ -71,7 +114,7 @@ pub fn formated_error(kind string /*error or warn*/, emsg string, filepath strin
 			term.bold(term.bright_blue(kind))
 		}
 	}
-	final_msg := emsg
+	final_msg := if emanager.support_color { term.bold(emsg) } else { emsg }
 	final_context := if source_context.len > 0 { '\n$source_context' } else { '' }
 	//
 	return '$final_position $final_kind $final_msg $final_context'.trim_space()
diff --git a/vlib/v/util/util.v b/vlib/v/util/util.v
index 1272f3f247..932d40bd0b 100644
--- a/vlib/v/util/util.v
+++ b/vlib/v/util/util.v
@@ -158,3 +158,19 @@ pub fn path_of_executable(path string) string {
 	}
 	return path
 }
+
+pub fn read_file(file_path string) ?string {
+	mut raw_text := os.read_file(file_path) or {
+		return error('failed to open $file_path')
+	}
+	// BOM check
+	if raw_text.len >= 3 {
+		c_text := raw_text.str
+		if c_text[0] == 0xEF && c_text[1] == 0xBB && c_text[2] == 0xBF {
+			// skip three BOM bytes
+			offset_from_begin := 3
+			raw_text = tos(c_text[offset_from_begin], vstrlen(c_text) - offset_from_begin)
+		}
+	}
+	return raw_text
+}