compiler: print asserted source line on failure

vlib/compiler/compile_errors.v

@@ -96,7 +96,7 @@ fn (s &Scanner) error_with_col(msg string, col int) {
 	eprintln('${fullpath}:${s.line_nr + 1}:${col}: $final_message')
 	
 	if s.should_print_line_on_error && s.nlines > 0 {
-		context_start_line := imax(0,          (s.line_nr - error_context_before + 1 ))
+		context_start_line := imax(0,        (s.line_nr - error_context_before    ))
 		context_end_line   := imin(s.nlines-1, (s.line_nr + error_context_after + 1 ))
 		for cline := context_start_line; cline < context_end_line; cline++ {
 			line := '${(cline+1):5d}| ' + s.line( cline )
@@ -132,7 +132,13 @@ fn (s &Scanner) error_with_col(msg string, col int) {
 [inline] fn imin(a,b int) int { 	return if a < b { a } else { b } }
 
 fn (s &Scanner) get_error_filepath() string {
-	if s.should_print_relative_paths_on_error {
+	verror_paths_override := os.getenv('VERROR_PATHS')
+	use_relative_paths := match verror_paths_override {
+		'relative' { true }
+		'absolute' { false }
+		else { s.should_print_relative_paths_on_error }
+	}
+	if use_relative_paths {
 		workdir := os.getwd() + os.path_separator
 		if s.file_path.starts_with(workdir) {
 			return s.file_path.replace( workdir, '')
@@ -247,10 +253,11 @@ fn (s mut Scanner) get_scanner_pos_of_token(t &Token) ScannerPos {
 	/////////////////// which just returns a struct, and that works
 	/////////////////// in gcc and clang, but causes the TCC problem.
 
+	maxline := imin( s.nlines, tline + 2 * error_context_after)
 	for {
 		prevlinepos = s.pos
 		if s.pos >= s.text.len { break }		
-		if s.line_nr > tline { break }
+		if s.line_nr > maxline { break }
 		////////////////////////////////////////
 		if tline == s.line_nr {
 			sptoken = s.get_scanner_pos()

vlib/compiler/main.v

@@ -648,9 +648,12 @@ pub fn (v &V)  get_user_files() []string {
 	// libs, but we dont know	which libs need to be added yet
 	mut user_files := []string
 
+	if v.pref.is_test {
+		user_files << os.join(v.vroot,'vlib','compiler','preludes','tests_assertions.v')
+	}
+	
 	if v.pref.is_test && v.pref.is_stats {
-		user_files << os.join(v.vroot, 'vlib', 'benchmark', 'tests',
+		user_files << os.join(v.vroot,'vlib','compiler','preludes','tests_with_stats.v')
-			'always_imported.v')
 	}
 	
 	// v volt/slack_test.v: compile all .v files to get the environment

vlib/compiler/parser.v

@@ -3578,20 +3578,49 @@ fn (p mut Parser) assert_statement() {
 	tmp := p.get_tmp()
 	p.gen('bool $tmp = ')
 	p.check_types(p.bool_expression(), 'bool')
+	nline := p.scanner.line_nr
 	// TODO print "expected:  got" for failed tests
 	filename := cescaped_path(p.file_path)
-	p.genln(';
+	cfname:=p.cur_fn.name.replace('main__', '')
-\n
+	sourceline := p.scanner.line( nline - 1 ).replace('"', '\'')
 
+	if !p.pref.is_test {
+		// an assert used in a normal v program. no fancy formatting
+		p.genln(';\n
+/// sline: "$sourceline"
 if (!$tmp) {
-  println(tos2((byte *)"\\x1B[31mFAILED: $p.cur_fn.name() in $filename:$p.scanner.line_nr\\x1B[0m"));
 	g_test_fails++;
+	eprintln(tos3("${filename}:${p.scanner.line_nr}: FAILED: ${cfname}()"));
+	eprintln(tos3("Source: $sourceline"));
+    v_panic(tos3("An assertion failed."));
+	return;
+} else {
+	g_test_oks++;
+}
+')
+		return
+	}
+	
+	p.genln(';\n
+if (!$tmp) {
+  g_test_fails++;
+  main__cb_assertion_failed( 
+     tos3("$filename"), 
+     $p.scanner.line_nr, 
+     tos3("$sourceline"),
+     tos3("$p.cur_fn.name()")
+  );
   return;
   // TODO
   // Maybe print all vars in a test function if it fails?
 } else {
   g_test_oks++;
-  //println(tos2((byte *)"\\x1B[32mPASSED: $p.cur_fn.name()\\x1B[0m"));
+  main__cb_assertion_ok( 
+     tos3("$filename"), 
+     $p.scanner.line_nr, 
+     tos3("$sourceline"),
+     tos3("$p.cur_fn.name()")
+  );
 }
 
 ')

vlib/compiler/preludes/tests_assertions.v

@@ -0,0 +1,35 @@
+module main
+
+import os
+import term
+
+////////////////////////////////////////////////////////////////////
+/// This file will get compiled as part of the main program,
+/// for a _test.v file.
+/// The methods defined here are called back by the test program's
+/// assert statements, on each success/fail. The goal is to make
+/// customizing the look & feel of the assertions results easier,
+/// since it is done in normal V code, instead of in embedded C ...
+////////////////////////////////////////////////////////////////////
+
+fn cb_assertion_failed(filename string, line int, sourceline string, funcname string){
+	color_on := term.can_show_color_on_stderr()
+	use_relative_paths := match os.getenv('VERROR_PATHS') {
+		'absolute' { false }
+		else { true }
+	}
+	final_filename := if use_relative_paths { filename } else { os.realpath( filename ) }
+	final_funcname := funcname.replace('main__','')
+
+	mut fail_message := 'FAILED assertion'
+	if color_on { fail_message = term.bold(term.red(fail_message)) }
+	
+	eprintln('$final_filename:$line: $fail_message')
+	eprintln('Function: $final_funcname')
+	eprintln('Source  : $sourceline')
+}
+
+fn cb_assertion_ok(filename string, line int, sourceline string, funcname string){
+	//do nothing for now on an OK assertion
+	//println('OK ${line:5d}|$sourceline ')
+}

vlib/compiler/scanner.v

@@ -236,6 +236,12 @@ fn (s mut Scanner) skip_whitespace() {
 	}
 }
 
+fn (s mut Scanner) end_of_file() ScanRes {
+	s.pos = s.text.len
+	s.inc_line_number()
+	return scan_res(.eof, '')
+}
+
 fn (s mut Scanner) scan() ScanRes {
 	//if s.line_comment != '' {
 		//s.fgenln('// LC "$s.line_comment"')
@@ -246,7 +252,7 @@ fn (s mut Scanner) scan() ScanRes {
 	}
 	s.started = true
 	if s.pos >= s.text.len {
-		return scan_res(.eof, '')
+		return s.end_of_file()
 	}
 	if !s.inside_string {
 		s.skip_whitespace()
@@ -263,7 +269,7 @@ fn (s mut Scanner) scan() ScanRes {
 	s.skip_whitespace()
 	// end of file
 	if s.pos >= s.text.len {
-		return scan_res(.eof, '')
+		return s.end_of_file()
 	}
 	// handle each char
 	c := s.text[s.pos]
@@ -618,7 +624,7 @@ fn (s mut Scanner) scan() ScanRes {
 	}
 	$if windows {
 		if c == `\0` {
-			return scan_res(.eof, '')
+			return s.end_of_file()
 		}
 	}
 	mut msg := 'invalid character `${c.str()}`'
@@ -626,7 +632,7 @@ fn (s mut Scanner) scan() ScanRes {
 		msg += ', use \' to denote strings'
 	}
 	s.error(msg)
-	return scan_res(.eof, '')
+	return s.end_of_file()
 }
 
 fn (s &Scanner) current_column() int {
@@ -804,7 +810,9 @@ fn (s mut Scanner) inc_line_number() {
 	s.last_nl_pos = s.pos
 	s.line_nr++
 	s.line_ends   << s.pos
-	s.nlines++
+	if s.line_nr > s.nlines { 
+		s.nlines = s.line_nr
+	}
 }
 
 fn (s Scanner) line(n int) string {