v.gen.js: add source map creation support (inline only, no src) (#10384)

2023-08-10 21:13:21 +03:00 · 2021-06-10 07:33:46 +02:00 · 2021-06-10 07:33:46 +02:00 · 96c8d147b2
commit 96c8d147b2
parent 14519bbf5c
17 changed files with 1275 additions and 39 deletions
--- a/cmd/v/help/build-js.txt
+++ b/cmd/v/help/build-js.txt
@ -0,0 +1,22 @@
+Usage: v -b js [-options] ['run'] <target.v|target_directory> [run options]
+
+This command compiles the given target, along with their dependencies, into an Javascript source file.
+
+For more general build help, see also `v help build`.
+
+# Interfacing the Javascript Backend code generation, passing options to it:
+   -prod
+      Do not create any JS Doc comments
+
+   -sourcemap
+      Create a source map for debugging
+
+   -sourcemap-inline
+      Embed the source map directly into the JavaScript source file 
+      (currently default, external source map files not implemented)
+
+   -sourcemap-src-include
+      Include the orginal V source files into the generated source map 
+      (default false, all files in the source map are currently referenced by their absolute system file path)
+
+      The supported targets for the JS backend are: ES5 strict
--- a/vlib/builtin/js/jsfns.js.v
+++ b/vlib/builtin/js/jsfns.js.v
@ -21,6 +21,15 @@ pub struct JS.Array {

 pub struct JS.Map {}

+// browser: https://developer.mozilla.org/de/docs/Web/JavaScript/Reference/Global_Objects/Error
+// node: https://nodejs.org/api/errors.html#errors_class_error
+pub struct JS.Error {
+pub:
+	name    string
+	message string
+	stack   string
+}
+
 // Type prototype functions
 fn (v JS.String) toString() JS.String
 fn (v JS.Number) toString() JS.String
--- a/vlib/builtin/js/jsfns_node.js.v
+++ b/vlib/builtin/js/jsfns_node.js.v
@ -7,6 +7,23 @@

 module builtin

+pub struct JS.node_process {
+pub:
+	arch     string
+	argsv    []string
+	env      []string
+	platform string
+	version  string
+	// TODO: add all properties
+}
+
+// hack to access  process properties
+pub fn js_node_process() JS.node_process {
+	#return process
+
+	return JS.node_process{}
+}
+
 fn JS.process.exit(int)
 fn JS.process.stdout.write(string) bool
 fn JS.process.stdout.writeln(string) bool
--- a/vlib/os/file.c.v
+++ b/vlib/os/file.c.v
@ -166,6 +166,15 @@ pub fn stderr() File {
 	}
 }

+// read implements the Reader interface.
+pub fn (f &File) read(mut buf []byte) ?int {
+	if buf.len == 0 {
+		return 0
+	}
+	nbytes := fread(buf.data, 1, buf.len, f.cfile) ?
+	return nbytes
+}
+
 // **************************** Write ops  ***************************
 // write implements the Writer interface.
 // It returns how many bytes were actually written.
@ -439,15 +448,6 @@ pub fn (f &File) read_bytes_into(pos u64, mut buf []byte) ?int {
 	return error('Could not read file')
 }

-// read implements the Reader interface.
-pub fn (f &File) read(mut buf []byte) ?int {
-	if buf.len == 0 {
-		return 0
-	}
-	nbytes := fread(buf.data, 1, buf.len, f.cfile) ?
-	return nbytes
-}
-
 // read_at reads `buf.len` bytes starting at file byte offset `pos`, in `buf`.
 [deprecated: 'use File.read_from() instead']
 pub fn (f &File) read_at(pos u64, mut buf []byte) ?int {
--- a/vlib/v/gen/js/js.v
+++ b/vlib/v/gen/js/js.v
@ -6,6 +6,8 @@ import v.token
 import v.pref
 import v.util
 import v.depgraph
+import encoding.base64
+import v.gen.js.sourcemap

 const (
 	// https://ecma-international.org/ecma-262/#sec-reserved-words
@ -22,14 +24,21 @@ const (
 		.int_literal, .float_literal, .size_t, .bool, .string]
 )

+struct SourcemapHelper {
+	src_path string
+	src_line u32
+	ns_pos   u32
+}
+
 struct Namespace {
 	name string
 mut:
-	out      strings.Builder = strings.new_builder(128)
-	pub_vars []string
-	imports  map[string]string
-	indent   int
-	methods  map[string][]ast.FnDecl
+	out              strings.Builder = strings.new_builder(128)
+	pub_vars         []string
+	imports          map[string]string
+	indent           int
+	methods          map[string][]ast.FnDecl
+	sourcemap_helper []SourcemapHelper
 }

 [heap]
@ -60,6 +69,8 @@ mut:
 	empty_line          bool
 	cast_stack          []ast.Type
 	call_stack          []ast.CallExpr
+	is_vlines_enabled   bool // is it safe to generate #line directives when -g is passed
+	sourcemap           sourcemap.SourceMap // maps lines in generated javascrip file to original source files and line
 }

 pub fn gen(files []&ast.File, table &ast.Table, pref &pref.Preferences) string {
@ -78,9 +89,14 @@ pub fn gen(files []&ast.File, table &ast.Table, pref &pref.Preferences) string {
 	// TODO: Add '[-no]-jsdoc' flag
 	if pref.is_prod {
 		g.enable_doc = false
+		g.is_vlines_enabled = false
 	}
 	g.init()
 	mut graph := depgraph.new_dep_graph()
+	if g.pref.sourcemap {
+		mut sg := sourcemap.generate_empty_map()
+		g.sourcemap = sg.add_map('', '', g.pref.sourcemap_src_included, 0, 0)
+	}
 	// Get class methods
 	for file in files {
 		g.file = file
@ -135,8 +151,29 @@ pub fn gen(files []&ast.File, table &ast.Table, pref &pref.Preferences) string {
 			out += val
 		}
 		out += ') {\n\t'
-		// private scope
-		out += namespace.out.str().trim_space()
+		namespace_code := namespace.out.str()
+		if g.pref.sourcemap {
+			// calculate current output start line
+			mut current_line := u32(out.count('\n') + 1)
+			mut sm_pos := u32(0)
+			for sourcemap_ns_entry in namespace.sourcemap_helper {
+				// calculate final generated location in output based on position
+				current_segment := namespace_code.substr(int(sm_pos), int(sourcemap_ns_entry.ns_pos))
+				current_line += u32(current_segment.count('\n'))
+				current_column := if last_nl_pos := current_segment.last_index('\n') {
+					u32(current_segment.len - last_nl_pos - 1)
+				} else {
+					u32(0)
+				}
+				g.sourcemap.add_mapping(sourcemap_ns_entry.src_path, sourcemap.SourcePosition{
+					source_line: sourcemap_ns_entry.src_line
+					source_column: 0 // sourcemap_ns_entry.src_column
+				}, current_line, current_column, '')
+				sm_pos = sourcemap_ns_entry.ns_pos
+			}
+		}
+		out += namespace_code
+
 		// public scope
 		out += '\n'
 		if g.enable_doc {
@ -195,6 +232,18 @@ pub fn gen(files []&ast.File, table &ast.Table, pref &pref.Preferences) string {
 		out += 'if (typeof module === "object" && module.exports) module.exports = $export;\n'
 	}
 	out += '\n'
+	if g.pref.sourcemap {
+		out += g.create_sourcemap()
+	}
+	return out
+}
+
+fn (g JsGen) create_sourcemap() string {
+	mut sm := g.sourcemap
+	mut out := '\n//# sourceMappingURL=data:application/json;base64,'
+	out += base64.encode(sm.to_json().str().bytes())
+	out += '\n'
+
 	return out
 }

@ -354,6 +403,21 @@ fn (mut g JsGen) stmts(stmts []ast.Stmt) {
 	g.dec_indent()
 }

+[inline]
+fn (mut g JsGen) write_v_source_line_info(pos token.Position) {
+	// g.inside_ternary == 0 &&
+	if g.pref.sourcemap {
+		g.ns.sourcemap_helper << SourcemapHelper{
+			src_path: util.vlines_escape_path(g.file.path, g.pref.ccompiler)
+			src_line: u32(pos.line_nr + 1)
+			ns_pos: u32(g.ns.out.len)
+		}
+	}
+	if g.pref.is_vlines && g.is_vlines_enabled {
+		g.write(' /* ${pos.line_nr + 1} $g.ns.out.len */ ')
+	}
+}
+
 fn (mut g JsGen) stmt(node ast.Stmt) {
 	g.stmt_start_pos = g.ns.out.len
 	match node {
@ -362,45 +426,56 @@ fn (mut g JsGen) stmt(node ast.Stmt) {
 			panic('inline asm is not supported by js')
 		}
 		ast.AssertStmt {
+			g.write_v_source_line_info(node.pos)
 			g.gen_assert_stmt(node)
 		}
 		ast.AssignStmt {
+			g.write_v_source_line_info(node.pos)
 			g.gen_assign_stmt(node)
 		}
 		ast.Block {
+			g.write_v_source_line_info(node.pos)
 			g.gen_block(node)
 			g.writeln('')
 		}
 		ast.BranchStmt {
+			g.write_v_source_line_info(node.pos)
 			g.gen_branch_stmt(node)
 		}
 		ast.CompFor {}
 		ast.ConstDecl {
+			g.write_v_source_line_info(node.pos)
 			g.gen_const_decl(node)
 		}
 		ast.DeferStmt {
 			g.defer_stmts << node
 		}
 		ast.EnumDecl {
+			g.write_v_source_line_info(node.pos)
 			g.gen_enum_decl(node)
 			g.writeln('')
 		}
 		ast.ExprStmt {
+			g.write_v_source_line_info(node.pos)
 			g.gen_expr_stmt(node)
 		}
 		ast.FnDecl {
+			g.write_v_source_line_info(node.pos)
 			g.fn_decl = unsafe { &node }
 			g.gen_fn_decl(node)
 		}
 		ast.ForCStmt {
+			g.write_v_source_line_info(node.pos)
 			g.gen_for_c_stmt(node)
 			g.writeln('')
 		}
 		ast.ForInStmt {
+			g.write_v_source_line_info(node.pos)
 			g.gen_for_in_stmt(node)
 			g.writeln('')
 		}
 		ast.ForStmt {
+			g.write_v_source_line_info(node.pos)
 			g.gen_for_stmt(node)
 			g.writeln('')
 		}
@ -408,18 +483,21 @@ fn (mut g JsGen) stmt(node ast.Stmt) {
 			// TODO
 		}
 		ast.GotoLabel {
+			g.write_v_source_line_info(node.pos)
 			g.writeln('${g.js_name(node.name)}:')
 		}
 		ast.GotoStmt {
 			// skip: JS has no goto
 		}
 		ast.HashStmt {
+			g.write_v_source_line_info(node.pos)
 			g.gen_hash_stmt(node)
 		}
 		ast.Import {
 			g.ns.imports[node.mod] = node.alias
 		}
 		ast.InterfaceDecl {
+			g.write_v_source_line_info(node.pos)
 			g.gen_interface_decl(node)
 		}
 		ast.Module {
@ -434,6 +512,7 @@ fn (mut g JsGen) stmt(node ast.Stmt) {
 		}
 		ast.SqlStmt {}
 		ast.StructDecl {
+			g.write_v_source_line_info(node.pos)
 			g.gen_struct_decl(node)
 		}
 		ast.TypeDecl {
--- a/vlib/v/gen/js/jsgen_test.v
+++ b/vlib/v/gen/js/jsgen_test.v
@ -1,9 +1,10 @@
 import os

 const (
-	test_dir   = os.join_path('vlib', 'v', 'gen', 'js', 'tests')
-	output_dir = '_js_tests/'
-	v_options  = '-b js -w'
+	test_dir     = os.join_path('vlib', 'v', 'gen', 'js', 'tests')
+	output_dir   = '_js_tests/'
+	v_options    = '-b js -w'
+	node_options = ''
 )

 fn testsuite_end() {
@ -12,6 +13,8 @@ fn testsuite_end() {

 const there_is_node_available = is_nodejs_working()

+const there_is_grep_available = is_grep_working()
+
 fn test_example_compilation() {
 	vexe := os.getenv('VEXE')
 	os.chdir(os.dir(vexe))
@ -20,7 +23,17 @@ fn test_example_compilation() {
 	for file in files {
 		path := os.join_path(test_dir, file)
 		println('Testing $file')
-		v_code := os.system('$vexe $v_options -o $output_dir${file}.js $path')
+		mut v_options_file := v_options
+		mut node_options_file := node_options
+		should_create_source_map := file.ends_with('_sourcemap.v')
+		if should_create_source_map {
+			println('activate -sourcemap creation')
+			v_options_file += ' -sourcemap' // activate souremap generation
+
+			println('add node option: --enable-source-maps') // requieres node >=12.12.0
+			node_options_file += ' --enable-source-maps' // activate souremap generation
+		}
+		v_code := os.system('$vexe $v_options_file -o $output_dir${file}.js $path')
 		if v_code != 0 {
 			assert false
 		}
@ -36,6 +49,15 @@ fn test_example_compilation() {
 		}
 		// Running failed
 		assert js_code == 0
+		if should_create_source_map {
+			if there_is_grep_available {
+				grep_code_sourcemap_found := os.system('grep -q -E "//#\\ssourceMappingURL=data:application/json;base64,[-A-Za-z0-9+/=]+$" $output_dir${file}.js')
+				assert grep_code_sourcemap_found == 0
+				println('file has a source map embeded')
+			} else {
+				println(' ... skipping testing for sourcemap $file, there is no grep present')
+			}
+		}
 	}
 }

@ -54,3 +76,11 @@ fn is_nodejs_working() bool {
 	}
 	return true
 }
+
+fn is_grep_working() bool {
+	node_res := os.execute('grep --version')
+	if node_res.exit_code != 0 {
+		return false
+	}
+	return true
+}
--- a/vlib/v/gen/js/sourcemap/basic_test.v
+++ b/vlib/v/gen/js/sourcemap/basic_test.v
@ -0,0 +1,158 @@
+module sourcemap
+
+fn test_simple() {
+	mut sg := generate_empty_map()
+	mut sm := sg.add_map('hello.js', '/', true, 0, 0)
+	sm.set_source_content('hello.v', "fn main(){nprintln('Hello World! Helo \$a')\n}")
+
+	mlist := [
+		MappingInput{
+			GenPosition: GenPosition{
+				gen_line: 1
+				gen_column: 0
+			}
+			name: ''
+			source_position: SourcePosition{
+				source_line: 1
+				source_column: 0
+			}
+		},
+		MappingInput{
+			GenPosition: GenPosition{
+				gen_line: 2
+				gen_column: 0
+			}
+			name: ''
+			source_position: SourcePosition{
+				source_line: 1
+				source_column: 0
+			}
+		},
+		MappingInput{
+			GenPosition: GenPosition{
+				gen_line: 2
+				gen_column: 2
+			}
+			name: ''
+			source_position: SourcePosition{
+				source_line: 1
+				source_column: 0
+			}
+		},
+		MappingInput{
+			GenPosition: GenPosition{
+				gen_line: 2
+				gen_column: 9
+			}
+			name: ''
+			source_position: SourcePosition{
+				source_line: 1
+				source_column: 7
+			}
+		},
+		MappingInput{
+			GenPosition: GenPosition{
+				gen_line: 2
+				gen_column: 10
+			}
+			name: 'hello_name'
+			source_position: SourcePosition{
+				source_line: 1
+				source_column: 8
+			}
+		},
+		MappingInput{
+			GenPosition: GenPosition{
+				gen_line: 2
+				gen_column: 13
+			}
+			name: ''
+			source_position: SourcePosition{
+				source_line: 1
+				source_column: 0
+			}
+		},
+		MappingInput{
+			GenPosition: GenPosition{
+				gen_line: 2
+				gen_column: 14
+			}
+			name: ''
+			source_position: SourcePosition{
+				source_line: 1
+				source_column: 12
+			}
+		},
+		MappingInput{
+			GenPosition: GenPosition{
+				gen_line: 2
+				gen_column: 27
+			}
+			name: ''
+			source_position: SourcePosition{
+				source_line: 1
+				source_column: 0
+			}
+		},
+		MappingInput{
+			GenPosition: GenPosition{
+				gen_line: 2
+				gen_column: 28
+			}
+			name: ''
+			source_position: SourcePosition{
+				source_line: 1
+				source_column: 0
+			}
+		},
+		MappingInput{
+			GenPosition: GenPosition{
+				gen_line: 2
+				gen_column: 29
+			}
+			name: ''
+			source_position: SourcePosition{
+				source_line: 1
+				source_column: 0
+			}
+		},
+		MappingInput{
+			GenPosition: GenPosition{
+				gen_line: 3
+				gen_column: 0
+			}
+			name: ''
+			source_position: SourcePosition{
+				source_line: 1
+				source_column: 0
+			}
+		},
+	]
+	sm.add_mapping_list('hello.v', mlist) or { panic('x') }
+
+	json_data := sm.to_json()
+
+	expected := '{"version":3,"file":"hello.js","sourceRoot":"\\/","sources":["hello.v"],"sourcesContent":["fn main(){nprintln(\'Hello World! Helo \$a\')\\n}"],"names":["hello_name"],"mappings":"AAAA;AAAA,EAAA,OAAO,CAACA,GAAR,CAAY,aAAZ,CAAA,CAAA;AAAA"}'
+	assert json_data.str() == expected
+}
+
+fn test_source_null() {
+	mut sg := generate_empty_map()
+	mut sm := sg.add_map('hello.js', '/', true, 0, 0)
+	sm.add_mapping('hello.v', SourcePosition{
+		source_line: 0
+		source_column: 0
+	}, 1, 1, '')
+	sm.add_mapping('hello_lib1.v', SourcePosition{
+		source_line: 0
+		source_column: 0
+	}, 2, 1, '')
+	sm.add_mapping('hello_lib2.v', SourcePosition{
+		source_line: 0
+		source_column: 0
+	}, 3, 1, '')
+	json_data := sm.to_json()
+
+	expected := '{"version":3,"file":"hello.js","sourceRoot":"\\/","sources":["hello.v","hello_lib1.v","hello_lib2.v"],"sourcesContent":[null,null,null],"names":[],"mappings":"CA+\\/\\/\\/\\/\\/HA;CCAA;CCAA"}'
+	assert json_data.str() == expected
+}
--- a/vlib/v/gen/js/sourcemap/compare_test.v
+++ b/vlib/v/gen/js/sourcemap/compare_test.v
@ -0,0 +1,322 @@
+module sourcemap
+
+fn test_cmp_eq() {
+	a := Mapping{
+		GenPosition: GenPosition{
+			gen_line: 1
+			gen_column: 0
+		}
+		sources_ind: 2
+		names_ind: IndexNumber(3)
+		source_position: SourcePosition{
+			source_line: 4
+			source_column: 5
+		}
+	}
+
+	b := Mapping{
+		GenPosition: GenPosition{
+			gen_line: 1
+			gen_column: 0
+		}
+		sources_ind: 2
+		names_ind: IndexNumber(3)
+		source_position: SourcePosition{
+			source_line: 4
+			source_column: 5
+		}
+	}
+
+	assert !compare_by_generated_positions_inflated(a, b)
+}
+
+fn test_cmp_name() {
+	a := Mapping{
+		GenPosition: GenPosition{
+			gen_line: 1
+			gen_column: 0
+		}
+		sources_ind: 2
+		names_ind: IndexNumber(3)
+		source_position: SourcePosition{
+			source_line: 4
+			source_column: 5
+		}
+	}
+
+	b := Mapping{
+		GenPosition: GenPosition{
+			gen_line: 1
+			gen_column: 0
+		}
+		sources_ind: 2
+		names_ind: IndexNumber(4)
+		source_position: SourcePosition{
+			source_line: 4
+			source_column: 5
+		}
+	}
+
+	assert compare_by_generated_positions_inflated(a, b)
+}
+
+fn test_cmp_name_empty() {
+	a := Mapping{
+		GenPosition: GenPosition{
+			gen_line: 1
+			gen_column: 0
+		}
+		sources_ind: 2
+		names_ind: IndexNumber(3)
+		source_position: SourcePosition{
+			source_line: 4
+			source_column: 5
+		}
+	}
+
+	b := Mapping{
+		GenPosition: GenPosition{
+			gen_line: 1
+			gen_column: 0
+		}
+		sources_ind: 2
+		names_ind: Empty{}
+		source_position: SourcePosition{
+			source_line: 4
+			source_column: 5
+		}
+	}
+
+	assert compare_by_generated_positions_inflated(a, b)
+}
+
+fn test_cmp_name_empty_empty() {
+	a := Mapping{
+		GenPosition: GenPosition{
+			gen_line: 1
+			gen_column: 0
+		}
+		sources_ind: 2
+		names_ind: Empty{}
+		source_position: SourcePosition{
+			source_line: 4
+			source_column: 5
+		}
+	}
+
+	b := Mapping{
+		GenPosition: GenPosition{
+			gen_line: 1
+			gen_column: 0
+		}
+		sources_ind: 2
+		names_ind: Empty{}
+		source_position: SourcePosition{
+			source_line: 4
+			source_column: 5
+		}
+	}
+
+	assert !compare_by_generated_positions_inflated(a, b)
+}
+
+fn test_cmp_source_position_empty_eq() {
+	a := Mapping{
+		GenPosition: GenPosition{
+			gen_line: 1
+			gen_column: 0
+		}
+		sources_ind: 2
+		names_ind: Empty{}
+		source_position: Empty{}
+	}
+
+	b := Mapping{
+		GenPosition: GenPosition{
+			gen_line: 1
+			gen_column: 0
+		}
+		sources_ind: 2
+		names_ind: Empty{}
+		source_position: Empty{}
+	}
+
+	assert !compare_by_generated_positions_inflated(a, b)
+}
+
+fn test_cmp_source_position_empty_diff() {
+	a := Mapping{
+		GenPosition: GenPosition{
+			gen_line: 1
+			gen_column: 0
+		}
+		sources_ind: 2
+		names_ind: Empty{}
+		source_position: SourcePosition{
+			source_line: 4
+			source_column: 5
+		}
+	}
+
+	b := Mapping{
+		GenPosition: GenPosition{
+			gen_line: 1
+			gen_column: 0
+		}
+		sources_ind: 2
+		names_ind: Empty{}
+		source_position: Empty{}
+	}
+
+	assert compare_by_generated_positions_inflated(a, b)
+}
+
+fn test_cmp_source_position_column_diff() {
+	a := Mapping{
+		GenPosition: GenPosition{
+			gen_line: 1
+			gen_column: 0
+		}
+		sources_ind: 2
+		names_ind: Empty{}
+		source_position: SourcePosition{
+			source_line: 4
+			source_column: 5
+		}
+	}
+
+	b := Mapping{
+		GenPosition: GenPosition{
+			gen_line: 1
+			gen_column: 0
+		}
+		sources_ind: 2
+		names_ind: Empty{}
+		source_position: SourcePosition{
+			source_line: 4
+			source_column: 99
+		}
+	}
+
+	assert compare_by_generated_positions_inflated(a, b)
+}
+
+fn test_cmp_source_position_line_diff() {
+	a := Mapping{
+		GenPosition: GenPosition{
+			gen_line: 1
+			gen_column: 0
+		}
+		sources_ind: 2
+		names_ind: Empty{}
+		source_position: SourcePosition{
+			source_line: 4
+			source_column: 5
+		}
+	}
+
+	b := Mapping{
+		GenPosition: GenPosition{
+			gen_line: 1
+			gen_column: 0
+		}
+		sources_ind: 2
+		names_ind: Empty{}
+		source_position: SourcePosition{
+			source_line: 88
+			source_column: 99
+		}
+	}
+
+	assert compare_by_generated_positions_inflated(a, b)
+}
+
+fn test_cmp_sources() {
+	a := Mapping{
+		GenPosition: GenPosition{
+			gen_line: 1
+			gen_column: 0
+		}
+		sources_ind: 2
+		names_ind: Empty{}
+		source_position: SourcePosition{
+			source_line: 4
+			source_column: 5
+		}
+	}
+
+	b := Mapping{
+		GenPosition: GenPosition{
+			gen_line: 1
+			gen_column: 0
+		}
+		sources_ind: 99
+		names_ind: Empty{}
+		source_position: SourcePosition{
+			source_line: 4
+			source_column: 5
+		}
+	}
+
+	assert compare_by_generated_positions_inflated(a, b)
+}
+
+fn test_cmp_gen_column() {
+	a := Mapping{
+		GenPosition: GenPosition{
+			gen_line: 1
+			gen_column: 0
+		}
+		sources_ind: 2
+		names_ind: Empty{}
+		source_position: SourcePosition{
+			source_line: 4
+			source_column: 5
+		}
+	}
+
+	b := Mapping{
+		GenPosition: GenPosition{
+			gen_line: 1
+			gen_column: 99
+		}
+		sources_ind: 2
+		names_ind: Empty{}
+		source_position: SourcePosition{
+			source_line: 4
+			source_column: 5
+		}
+	}
+
+	assert compare_by_generated_positions_inflated(a, b)
+}
+
+fn test_cmp_gen_line() {
+	a := Mapping{
+		GenPosition: GenPosition{
+			gen_line: 1
+			gen_column: 0
+		}
+		sources_ind: 2
+		names_ind: Empty{}
+		source_position: SourcePosition{
+			source_line: 4
+			source_column: 5
+		}
+	}
+
+	b := Mapping{
+		GenPosition: GenPosition{
+			gen_line: 1
+			gen_column: 99
+		}
+		sources_ind: 2
+		names_ind: Empty{}
+		source_position: SourcePosition{
+			source_line: 4
+			source_column: 5
+		}
+	}
+
+	assert compare_by_generated_positions_inflated(a, b)
+}
--- a/vlib/v/gen/js/sourcemap/mappings.v
+++ b/vlib/v/gen/js/sourcemap/mappings.v
@ -0,0 +1,169 @@
+module sourcemap
+
+import v.gen.js.sourcemap.vlq
+import io
+
+struct Empty {}
+
+pub struct SourcePosition {
+	source_line   u32
+	source_column u32
+}
+
+type IndexNumber = u32
+type SourcePositionType = Empty | SourcePosition
+type NameIndexType = Empty | IndexNumber
+
+struct GenPosition {
+	gen_line   u32
+	gen_column u32
+}
+
+struct MappingInput {
+	GenPosition
+	name            string
+	source_position SourcePositionType
+}
+
+struct Mapping {
+	GenPosition
+	sources_ind     u32
+	names_ind       NameIndexType
+	source_position SourcePositionType
+}
+
+struct Mappings {
+mut:
+	sorted bool
+	last   Mapping
+	values []Mapping
+}
+
+fn new_mappings() Mappings {
+	return Mappings{
+		last: Mapping{
+			GenPosition: {
+				gen_column: 0
+				gen_line: 0
+			}
+		}
+		sorted: true
+	}
+}
+
+// Add the given source mapping
+fn (mut m Mappings) add_mapping(gen_line u32, gen_column u32, sources_ind u32, source_position SourcePositionType, names_ind NameIndexType) {
+	if !(gen_line > m.last.gen_line
+		|| (gen_line == m.last.gen_line && gen_column >= m.last.gen_column)) {
+		m.sorted = false
+	}
+	m.values << Mapping{
+		GenPosition: GenPosition{
+			gen_line: gen_line
+			gen_column: gen_column
+		}
+		sources_ind: sources_ind
+		names_ind: names_ind
+		source_position: source_position
+	}
+}
+
+// Returns the flat, sorted array of mappings. The mappings are sorted by generated position.
+
+fn (mut m Mappings) get_sorted_array() []Mapping {
+	if !m.sorted {
+		panic('not implemented')
+	}
+	return m.values
+}
+
+fn (mut m Mappings) export_mappings(mut output io.Writer) ? {
+	mut previous_generated_line := u32(1)
+	mut previous_generated_column := u32(0)
+	mut previous_source_index := i64(0)
+	mut previous_source_line := i64(0)
+	mut previous_source_column := i64(0)
+	mut previous_name_index := i64(0)
+
+	line_mappings := m.get_sorted_array()
+	len := line_mappings.len
+	for i := 0; i < len; i++ {
+		mapping := line_mappings[i]
+
+		cloned_generated_line := mapping.gen_line
+		if cloned_generated_line > 0 {
+			// Write a ';' for each line between this and last line, way more efficient than storing empty lines or looping...
+			output.write(';'.repeat(int(cloned_generated_line - previous_generated_line)).bytes()) or {
+				panic('Writing vql failed!')
+			}
+		}
+		if cloned_generated_line != previous_generated_line {
+			previous_generated_column = 0
+			previous_generated_line = cloned_generated_line
+		} else {
+			if i > 0 {
+				if !compare_by_generated_positions_inflated(mapping, line_mappings[i - 1]) {
+					continue
+				}
+				output.write(','.bytes()) or { panic('Writing vql failed!') }
+			}
+		}
+
+		vlq.encode(i64(mapping.gen_column - previous_generated_column), mut &output) ?
+		previous_generated_column = mapping.gen_column
+		match mapping.source_position {
+			Empty {}
+			SourcePosition {
+				vlq.encode(i64(mapping.sources_ind - previous_source_index), mut &output) ?
+				previous_source_index = mapping.sources_ind
+				// lines are stored 0-based in SourceMap spec version 3
+				vlq.encode(i64(mapping.source_position.source_line - 1 - previous_source_line), mut
+					output) ?
+				previous_source_line = mapping.source_position.source_line - 1
+				vlq.encode(i64(mapping.source_position.source_column - previous_source_column), mut
+					output) ?
+				previous_source_column = mapping.source_position.source_column
+
+				match mapping.names_ind {
+					Empty {}
+					IndexNumber {
+						vlq.encode(i64(mapping.names_ind - previous_name_index), mut &output) ?
+						previous_name_index = mapping.names_ind
+					}
+				}
+			}
+		}
+	}
+}
+
+fn compare_by_generated_positions_inflated(mapping_a Mapping, mapping_b Mapping) bool {
+	if mapping_a.gen_line != mapping_b.gen_line {
+		return true
+	}
+	if mapping_a.gen_column != mapping_b.gen_column {
+		return true
+	}
+
+	if mapping_a.sources_ind != mapping_b.sources_ind {
+		return true
+	}
+
+	if mapping_a.source_position.type_name() == mapping_b.source_position.type_name()
+		&& mapping_b.source_position is SourcePosition {
+		if
+			(mapping_a.source_position as SourcePosition).source_line != (mapping_b.source_position as SourcePosition).source_line || (mapping_a.source_position as SourcePosition).source_column != (mapping_b.source_position as SourcePosition).source_column {
+			return true
+		}
+	} else {
+		if mapping_a.source_position.type_name() != mapping_b.source_position.type_name() {
+			return true
+		}
+	}
+
+	if mapping_a.names_ind.type_name() == mapping_b.names_ind.type_name()
+		&& mapping_a.names_ind is IndexNumber {
+		return (mapping_a.names_ind as IndexNumber) != (mapping_b.names_ind as IndexNumber)
+	} else {
+		return mapping_a.names_ind.type_name() != mapping_b.names_ind.type_name()
+	}
+}
--- a/vlib/v/gen/js/sourcemap/sets.v
+++ b/vlib/v/gen/js/sourcemap/sets.v
@ -0,0 +1,16 @@
+module sourcemap
+
+struct Sets {
+mut:
+	value map[string]u32
+}
+
+// adds a new element to a Set if new and returns index position of new or existing element
+fn (mut s Sets) add(element string) u32 {
+	index := s.value[element] or {
+		index := u32(s.value.len)
+		s.value[element] = index
+		return index
+	}
+	return index
+}
--- a/vlib/v/gen/js/sourcemap/source_map.v
+++ b/vlib/v/gen/js/sourcemap/source_map.v
@ -0,0 +1,131 @@
+module sourcemap
+
+import io
+import os
+import x.json2
+
+const (
+	source_map_version = 3
+)
+
+type SourceMapJson = map[string]json2.Any
+
+struct SourceMap {
+pub mut:
+	version                int               [json: version]
+	file                   string            [json: file]
+	source_root            string            [json: source_root]
+	sources                Sets              [json: sources]
+	sources_content        map[string]string
+	names                  Sets
+	mappings               Mappings
+	sources_content_inline bool
+}
+
+struct StringWriter {
+pub mut:
+	bytes []byte
+}
+
+pub fn new_sourcemap(file string, source_root string, sources_content_inline bool) SourceMap {
+	return SourceMap{
+		version: sourcemap.source_map_version
+		file: file
+		source_root: source_root
+		mappings: new_mappings()
+		sources_content_inline: sources_content_inline
+	}
+}
+
+// Add a single mapping from original source line and column to the generated source's line and column for this source map being created.
+pub fn (mut sm SourceMap) add_mapping(source_name string, source_position SourcePositionType, gen_line u32, gen_column u32, name string) {
+	assert source_name.len != 0
+
+	sources_ind := sm.sources.add(source_name)
+
+	names_ind := if name.len != 0 {
+		NameIndexType(IndexNumber(sm.names.add(name)))
+	} else {
+		NameIndexType(Empty{})
+	}
+	sm.mappings.add_mapping(gen_line, gen_column, sources_ind, source_position, names_ind)
+}
+
+// Add multiple mappings from the same source
+pub fn (mut sm SourceMap) add_mapping_list(source_name string, mapping_list []MappingInput) ? {
+	assert source_name.len != 0
+
+	sources_ind := sm.sources.add(source_name)
+
+	for mapping in mapping_list {
+		names_ind := if mapping.name.len != 0 {
+			NameIndexType(IndexNumber(sm.names.add(mapping.name)))
+		} else {
+			NameIndexType(Empty{})
+		}
+		sm.mappings.add_mapping(mapping.gen_line, mapping.gen_column, sources_ind, mapping.source_position,
+			names_ind)
+	}
+}
+
+// Set the source content for a source file.
+pub fn (mut sm SourceMap) set_source_content(source_name string, source_content string) {
+	sm.sources_content[source_name] = source_content
+}
+
+fn (mut sm SourceMap) export_mappings(mut writer io.Writer) {
+	sm.mappings.export_mappings(mut writer) or { panic('export failed') }
+}
+
+fn (mut sm SourceMap) export_mappings_string() string {
+	mut output := StringWriter{}
+
+	sm.mappings.export_mappings(mut output) or { panic('export failed') }
+	return output.bytes.bytestr()
+}
+
+// create a JSON representing the sourcemap
+// Sourcemap Specs http://sourcemaps.info/spec.html
+pub fn (mut sm SourceMap) to_json() SourceMapJson {
+	mut source_map_json := map[string]json2.Any{}
+	source_map_json['version'] = sm.version
+	if sm.file != '' {
+		source_map_json['file'] = json2.Any(sm.file)
+	}
+	if sm.source_root != '' {
+		source_map_json['sourceRoot'] = json2.Any(sm.source_root)
+	}
+	mut sources_json := []json2.Any{}
+	mut sources_content_json := []json2.Any{}
+	for source_file, _ in sm.sources.value {
+		sources_json << source_file
+		if source_file in sm.sources_content {
+			sources_content_json << sm.sources_content[source_file]
+		} else {
+			if sm.sources_content_inline {
+				if source_file_content := os.read_file(source_file) {
+					sources_content_json << source_file_content
+				} else {
+					sources_content_json << json2.null
+				}
+			} else {
+				sources_content_json << json2.null
+			}
+		}
+	}
+	source_map_json['sources'] = json2.Any(sources_json)
+	source_map_json['sourcesContent'] = json2.Any(sources_content_json)
+
+	mut names_json := []json2.Any{}
+	for name, _ in sm.names.value {
+		names_json << name
+	}
+	source_map_json['names'] = json2.Any(names_json)
+	source_map_json['mappings'] = sm.export_mappings_string()
+	return source_map_json
+}
+
+fn (mut w StringWriter) write(buf []byte) ?int {
+	w.bytes << buf
+	return buf.len
+}
--- a/vlib/v/gen/js/sourcemap/source_map_generator.v
+++ b/vlib/v/gen/js/sourcemap/source_map_generator.v
@ -0,0 +1,46 @@
+module sourcemap
+
+struct V3 {
+	SourceMap
+pub:
+	sections []Section [json: sections]
+}
+
+struct Offset {
+pub mut:
+	line   int [json: line]
+	column int [json: column]
+}
+
+struct Section {
+pub mut:
+	offset     Offset    [json: offset]
+	source_map SourceMap [json: map]
+}
+
+struct Generator {
+mut:
+	file string
+	// source_root string
+	sections []Section
+}
+
+pub fn generate_empty_map() &Generator {
+	return &Generator{}
+}
+
+pub fn (mut g Generator) add_map(file string, source_root string, sources_content_inline bool, line_offset int, column_offset int) &SourceMap {
+	source_map := new_sourcemap(file, source_root, sources_content_inline)
+
+	offset := Offset{
+		line: line_offset
+		column: column_offset
+	}
+
+	g.sections << Section{
+		offset: offset
+		source_map: source_map
+	}
+
+	return &source_map
+}
--- a/vlib/v/gen/js/sourcemap/vlq/vlq.v
+++ b/vlib/v/gen/js/sourcemap/vlq/vlq.v
@ -0,0 +1,115 @@
+module vlq
+
+import io
+
+const (
+	shift                  = byte(5)
+	mask                   = byte((1 << shift) - 1)
+	continued              = byte(1 << shift)
+	max_i64                = u64(9223372036854775807)
+
+	// index start is: byte - vlq.enc_char_special_plus
+	enc_index              = [62, 0, 0, 0, 63, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 0, 0, 0,
+		0, 0, 0, 0, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21,
+		22, 23, 24, 25, 0, 0, 0, 0, 0, 0, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39,
+		40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51]!
+
+	enc_table              = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/'
+
+	enc_char_start_au      = 65
+	enc_char_end_zu        = 90
+	enc_char_start_al      = 97
+	enc_char_end_zl        = 122
+	enc_char_start_zero    = 48
+	enc_char_end_nine      = 57
+	enc_char_special_plus  = 43
+	enc_char_special_slash = 47
+)
+
+[inline]
+fn abs64(x i64) u64 {
+	return if x < 0 { u64(-x) } else { u64(x) }
+}
+
+// Decode a single base64 digit.
+[inline]
+fn decode64(input byte) byte {
+	$if debug {
+		assert input >= vlq.enc_char_special_plus
+		assert input <= vlq.enc_char_end_zl
+	}
+	return byte(vlq.enc_index[input - vlq.enc_char_special_plus])
+}
+
+// Decode a single VLQ value from the input stream, returning the value.
+//
+// # Range
+//
+// Supports all numbers that can be represented by a sign bit and a 63 bit
+// absolute value: `[-(2^63 - 1), 2^63 - 1]`.
+//
+// Note that `i64::MIN = -(2^63)` cannot be represented in that form, and this
+// NOT IMPLEMENTED: function will return `Error::Overflowed` when attempting to decode it.
+pub fn decode(mut input io.Reader) ?i64 {
+	mut buf := []byte{len: 1}
+
+	mut accum := u64(0)
+	mut shifter := 0
+	mut digit := byte(0)
+
+	mut keep_going := true
+	for keep_going {
+		len := input.read(mut buf) or { return error('Unexpected EOF') }
+		if len == 0 {
+			return error('no content')
+		}
+		digit = decode64(buf[0])
+		keep_going = (digit & vlq.continued) != 0
+
+		digit_value := u64(digit & vlq.mask) << u32(shifter) // TODO: check Overflow
+
+		accum += digit_value
+		shifter += vlq.shift
+	}
+
+	abs_value := accum / 2
+	if abs_value > vlq.max_i64 {
+		return error('Overflow')
+	}
+
+	// The low bit holds the sign.
+	return if (accum & 1) != 0 { (-i64(abs_value)) } else { i64(abs_value) }
+}
+
+[inline]
+fn encode64(input byte) byte {
+	$if debug {
+		assert input < 64
+	}
+	return vlq.enc_table[input]
+}
+
+// Encode a value as Base64 VLQ, sending it to the writer
+pub fn encode(value i64, mut output io.Writer) ? {
+	signed := value < 0
+	mut value_u64 := abs64(value) << 1
+	if signed {
+		if value_u64 == 0 {
+			// Wrapped
+			value_u64 = vlq.max_i64 + 1
+		}
+		value_u64 |= 1
+	}
+	for {
+		mut digit := byte(value_u64) & vlq.mask
+		value_u64 >>= vlq.shift
+		if value_u64 > 0 {
+			digit |= vlq.continued
+		}
+		bytes := [encode64(digit)]
+		output.write(bytes) or { return error('Write failed') }
+		if value_u64 == 0 {
+			break
+		}
+	}
+}
--- a/vlib/v/gen/js/sourcemap/vlq/vlq_decode_test.v
+++ b/vlib/v/gen/js/sourcemap/vlq/vlq_decode_test.v
@ -0,0 +1,52 @@
+module vlq
+
+import io
+
+struct TestReader {
+pub:
+	bytes []byte
+mut:
+	i int
+}
+
+struct TestData {
+	decode_val string
+	expected   i64
+}
+
+type TestDataList = []TestData
+
+fn test_decode_a() ? {
+	decode_values := [
+		TestData{'A', 0},
+		TestData{'C', 1},
+		TestData{'D', -1},
+		TestData{'2H', 123},
+		TestData{'qxmvrH', 123456789},
+		TestData{'+/////B', 1073741823} /* 2^30-1 */,
+		// TestData{'hgggggggggggI', 9_223_372_036_854_775_808} /* 2^63 */,
+	]
+
+	for _, test_data in decode_values {
+		mut input := make_test_reader(test_data.decode_val)
+
+		res := decode(mut &input) ?
+		assert res == test_data.expected
+	}
+}
+
+fn (mut b TestReader) read(mut buf []byte) ?int {
+	if !(b.i < b.bytes.len) {
+		return none
+	}
+	n := copy(buf, b.bytes[b.i..])
+	b.i += n
+	return n
+}
+
+fn make_test_reader(data string) io.Reader {
+	buf := &TestReader{
+		bytes: data.bytes()
+	}
+	return io.new_buffered_reader(reader: buf)
+}
--- a/vlib/v/gen/js/sourcemap/vlq/vlq_encode_test.v
+++ b/vlib/v/gen/js/sourcemap/vlq/vlq_encode_test.v
@ -0,0 +1,35 @@
+module vlq
+
+struct TestData {
+	expected string
+	data_val i64
+}
+
+struct TestWriter {
+pub mut:
+	bytes []byte
+}
+
+fn test_encode_a() ? {
+	decode_values := [
+		TestData{'A', 0},
+		TestData{'C', 1},
+		TestData{'D', -1},
+		TestData{'2H', 123},
+		TestData{'qxmvrH', 123456789},
+		TestData{'+/////B', 1073741823} /* 2^30-1 */,
+		// TestData{'hgggggggggggI', 9_223_372_036_854_775_808} /* 2^63 */,
+	]
+	for _, test_data in decode_values {
+		mut output := TestWriter{}
+
+		encode(test_data.data_val, mut &output) ?
+		// dump(output.bytes)
+		assert output.bytes == test_data.expected.bytes()
+	}
+}
+
+fn (mut w TestWriter) write(buf []byte) ?int {
+	w.bytes << buf
+	return buf.len
+}
--- a/vlib/v/gen/js/tests/simple_sourcemap.v
+++ b/vlib/v/gen/js/tests/simple_sourcemap.v
@ -0,0 +1,23 @@
+module main
+
+fn main() {
+	e := JS.Error{}
+	s := e.stack
+	node_version := js_node_process().version
+	node_main := get_node_main_version(node_version)
+	if node_main >= 12 {
+		if s.contains('simple_sourcemap.v:') {
+			panic('node found no source map!')
+		} else {
+			println('source map is working')
+		}
+	} else {
+		println('skiping test! node version >=12.12.0 required. Current Version is $node_version')
+	}
+}
+
+fn get_node_main_version(str string) int {
+	a := str.slice(1, int(str.len))
+	b := a.split('.')
+	return b[0].int()
+}
--- a/vlib/v/pref/pref.v
+++ b/vlib/v/pref/pref.v
@ -85,25 +85,28 @@ pub mut:
 	// verbosity           VerboseLevel
 	is_verbose bool
 	// nofmt            bool   // disable vfmt
-	is_test           bool   // `v test string_test.v`
-	is_script         bool   // single file mode (`v program.v`), main function can be skipped
-	is_vsh            bool   // v script (`file.vsh`) file, the `os` module should be made global
-	is_livemain       bool   // main program that contains live/hot code
-	is_liveshared     bool   // a shared library, that will be used in a -live main program
-	is_shared         bool   // an ordinary shared library, -shared, no matter if it is live or not
-	is_prof           bool   // benchmark every function
-	profile_file      string // the profile results will be stored inside profile_file
-	profile_no_inline bool   // when true, [inline] functions would not be profiled
-	translated        bool   // `v translate doom.v` are we running V code translated from C? allow globals, ++ expressions, etc
-	is_prod           bool   // use "-O2"
-	obfuscate         bool   // `v -obf program.v`, renames functions to "f_XXX"
-	is_repl           bool
-	is_run            bool
-	sanitize          bool // use Clang's new "-fsanitize" option
-	is_debug          bool // false by default, turned on by -g or -cg, it tells v to pass -g to the C backend compiler.
-	is_vlines         bool // turned on by -g, false by default (it slows down .tmp.c generation slightly).
-	show_cc           bool // -showcc, print cc command
-	show_c_output     bool // -show-c-output, print all cc output even if the code was compiled correctly
+	is_test                bool   // `v test string_test.v`
+	is_script              bool   // single file mode (`v program.v`), main function can be skipped
+	is_vsh                 bool   // v script (`file.vsh`) file, the `os` module should be made global
+	is_livemain            bool   // main program that contains live/hot code
+	is_liveshared          bool   // a shared library, that will be used in a -live main program
+	is_shared              bool   // an ordinary shared library, -shared, no matter if it is live or not
+	is_prof                bool   // benchmark every function
+	profile_file           string // the profile results will be stored inside profile_file
+	profile_no_inline      bool   // when true, [inline] functions would not be profiled
+	translated             bool   // `v translate doom.v` are we running V code translated from C? allow globals, ++ expressions, etc
+	is_prod                bool   // use "-O2"
+	obfuscate              bool   // `v -obf program.v`, renames functions to "f_XXX"
+	is_repl                bool
+	is_run                 bool
+	sanitize               bool // use Clang's new "-fsanitize" option
+	is_debug               bool // false by default, turned on by -g or -cg, it tells v to pass -g to the C backend compiler.
+	sourcemap              bool // JS Backend: -sourcemap will create a source map - default false
+	sourcemap_inline       bool = true // JS Backend: -sourcemap-inline will embed the source map in the generated JaaScript file -  currently default true only implemented
+	sourcemap_src_included bool // JS Backend: -sourcemap-src-included includes V source code in source map -  default false
+	is_vlines              bool // turned on by -g, false by default (it slows down .tmp.c generation slightly).
+	show_cc                bool // -showcc, print cc command
+	show_c_output          bool // -show-c-output, print all cc output even if the code was compiled correctly
 	// NB: passing -cg instead of -g will set is_vlines to false and is_debug to true, thus making v generate cleaner C files,
 	// which are sometimes easier to debug / inspect manually than the .tmp.c files by plain -g (when/if v line number generation breaks).
 	// use cached modules to speed up compilation.
@ -322,6 +325,15 @@ pub fn parse_args(known_external_commands []string, args []string) (&Preferences
 				res.show_cc = true
 				res.show_c_output = true
 			}
+			'-sourcemap' {
+				res.sourcemap = true
+			}
+			'-sourcemap-src-included' {
+				res.sourcemap_src_included = true
+			}
+			'-sourcemap-inline' {
+				res.sourcemap_inline = true
+			}
 			'-repl' {
 				res.is_repl = true
 			}