From 5841d5d8e1c581c14946a01bf51dccdd442cd6f4 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Daniel=20D=C3=A4schle?= <daniel.daeschle@gmail.com>
Date: Tue, 5 Jan 2021 15:11:43 +0100
Subject: [PATCH] all: implement basic comptime field selector (#7888)

---
 vlib/v/ast/ast.v                              | 23 ++++--
 vlib/v/ast/str.v                              |  3 +
 vlib/v/checker/checker.v                      | 34 ++++++++-
 ...comptime_field_selector_not_in_for_err.out |  7 ++
 .../comptime_field_selector_not_in_for_err.vv | 14 ++++
 .../comptime_field_selector_not_name_err.out  |  7 ++
 .../comptime_field_selector_not_name_err.vv   | 17 +++++
 vlib/v/fmt/fmt.v                              | 11 ++-
 .../fmt/tests/comptime_field_selector_keep.vv | 23 ++++++
 ...omptime_field_selector_parentheses_keep.vv | 23 ++++++
 vlib/v/gen/cgen.v                             |  8 ++-
 vlib/v/gen/comptime.v                         | 30 ++++++--
 vlib/v/gen/js/js.v                            |  3 +
 vlib/v/parser/comptime.v                      | 71 ++++++++-----------
 vlib/v/parser/parser.v                        |  2 +-
 vlib/v/tests/comptime_field_selector_test.v   | 62 ++++++++++++++++
 16 files changed, 281 insertions(+), 57 deletions(-)
 create mode 100644 vlib/v/checker/tests/comptime_field_selector_not_in_for_err.out
 create mode 100644 vlib/v/checker/tests/comptime_field_selector_not_in_for_err.vv
 create mode 100644 vlib/v/checker/tests/comptime_field_selector_not_name_err.out
 create mode 100644 vlib/v/checker/tests/comptime_field_selector_not_name_err.vv
 create mode 100644 vlib/v/fmt/tests/comptime_field_selector_keep.vv
 create mode 100644 vlib/v/fmt/tests/comptime_field_selector_parentheses_keep.vv
 create mode 100644 vlib/v/tests/comptime_field_selector_test.v

diff --git a/vlib/v/ast/ast.v b/vlib/v/ast/ast.v
index 52717d3ffb..f4f4028273 100644
--- a/vlib/v/ast/ast.v
+++ b/vlib/v/ast/ast.v
@@ -10,11 +10,11 @@ import v.errors
 pub type TypeDecl = AliasTypeDecl | FnTypeDecl | SumTypeDecl
 
 pub type Expr = AnonFn | ArrayDecompose | ArrayInit | AsCast | Assoc | AtExpr | BoolLiteral |
-	CTempVar | CallExpr | CastExpr | ChanInit | CharLiteral | Comment | ComptimeCall | ConcatExpr |
-	EnumVal | FloatLiteral | Ident | IfExpr | IfGuardExpr | IndexExpr | InfixExpr | IntegerLiteral |
-	Likely | LockExpr | MapInit | MatchExpr | None | OrExpr | ParExpr | PostfixExpr | PrefixExpr |
-	RangeExpr | SelectExpr | SelectorExpr | SizeOf | SqlExpr | StringInterLiteral | StringLiteral |
-	StructInit | Type | TypeOf | UnsafeExpr
+	CTempVar | CallExpr | CastExpr | ChanInit | CharLiteral | Comment | ComptimeCall | ComptimeSelector |
+	ConcatExpr | EnumVal | FloatLiteral | Ident | IfExpr | IfGuardExpr | IndexExpr | InfixExpr |
+	IntegerLiteral | Likely | LockExpr | MapInit | MatchExpr | None | OrExpr | ParExpr | PostfixExpr |
+	PrefixExpr | RangeExpr | SelectExpr | SelectorExpr | SizeOf | SqlExpr | StringInterLiteral |
+	StringLiteral | StructInit | Type | TypeOf | UnsafeExpr
 
 pub type Stmt = AssertStmt | AssignStmt | Block | BranchStmt | CompFor | ConstDecl | DeferStmt |
 	EnumDecl | ExprStmt | FnDecl | ForCStmt | ForInStmt | ForStmt | GlobalDecl | GoStmt |
@@ -1056,8 +1056,19 @@ pub mut:
 	val  string
 }
 
+pub struct ComptimeSelector {
+pub:
+	has_parens bool // if $() is used, for vfmt
+	left       Expr
+	field_expr Expr
+pub mut:
+	left_type  table.Type
+	typ        table.Type
+}
+
 pub struct ComptimeCall {
 pub:
+	has_parens  bool // if $() is used, for vfmt
 	method_name string
 	left        Expr
 	is_vweb     bool
@@ -1147,7 +1158,7 @@ pub fn (expr Expr) position() token.Position {
 		IfGuardExpr {
 			return expr.expr.position()
 		}
-		ComptimeCall {
+		ComptimeCall, ComptimeSelector {
 			return expr.left.position()
 		}
 		InfixExpr {
diff --git a/vlib/v/ast/str.v b/vlib/v/ast/str.v
index f75cd0e1d7..eae56fc4ce 100644
--- a/vlib/v/ast/str.v
+++ b/vlib/v/ast/str.v
@@ -212,6 +212,9 @@ pub fn (x Expr) str() string {
 		CharLiteral {
 			return '`$x.val`'
 		}
+		ComptimeSelector {
+			return '${x.left}.$$x.field_expr'
+		}
 		EnumVal {
 			return '.$x.val'
 		}
diff --git a/vlib/v/checker/checker.v b/vlib/v/checker/checker.v
index 8b42e8e484..b794047104 100644
--- a/vlib/v/checker/checker.v
+++ b/vlib/v/checker/checker.v
@@ -69,6 +69,7 @@ mut:
 	prevent_sum_type_unwrapping_once bool   // needed for assign new values to sum type, stopping unwrapping then
 	loop_label                       string // set when inside a labelled for loop
 	timers                           &util.Timers = util.new_timers(false)
+	comptime_fields_type             map[string]table.Type
 }
 
 pub fn new_checker(table &table.Table, pref &pref.Preferences) Checker {
@@ -979,6 +980,9 @@ fn (mut c Checker) fail_if_immutable(expr ast.Expr) (string, token.Position) {
 			// TODO
 			return '', pos
 		}
+		ast.ComptimeSelector {
+			return '', pos
+		}
 		ast.Ident {
 			if expr.obj is ast.Var {
 				mut v := expr.obj as ast.Var
@@ -3201,10 +3205,26 @@ pub fn (mut c Checker) expr(node ast.Expr) table.Type {
 			}
 			if node.method_name == 'html' {
 				return c.table.find_type_idx('vweb.Result')
-			} else {
-				return table.string_type
 			}
-			// return table.void_type
+			return table.string_type
+		}
+		ast.ComptimeSelector {
+			node.left_type = c.unwrap_generic(c.expr(node.left))
+			expr_type := c.unwrap_generic(c.expr(node.field_expr))
+			expr_sym := c.table.get_type_symbol(expr_type)
+			if expr_type != table.string_type {
+				c.error('expected `string` instead of `$expr_sym.name` (e.g. `field.name`)',
+					node.field_expr.position())
+			}
+			if node.field_expr is ast.SelectorExpr {
+				expr_name := node.field_expr.expr.str()
+				if expr_name in c.comptime_fields_type {
+					return c.comptime_fields_type[expr_name]
+				}
+			}
+			c.error('compile time field access can only be used when iterating over `T.fields`',
+				node.field_expr.position())
+			return table.void_type
 		}
 		ast.ConcatExpr {
 			return c.concat_expr(mut node)
@@ -4210,6 +4230,14 @@ pub fn (mut c Checker) if_expr(mut node ast.IfExpr) table.Type {
 			}
 		}
 		if node.is_comptime { // Skip checking if needed
+			// smartcast field type on comptime if
+			if branch.cond is ast.InfixExpr {
+				if branch.cond.op == .key_is {
+					se := branch.cond.left as ast.SelectorExpr
+					got_type := (branch.cond.right as ast.Type).typ
+					c.comptime_fields_type[se.expr.str()] = got_type
+				}
+			}
 			cur_skip_flags := c.skip_flags
 			if found_branch {
 				c.skip_flags = true
diff --git a/vlib/v/checker/tests/comptime_field_selector_not_in_for_err.out b/vlib/v/checker/tests/comptime_field_selector_not_in_for_err.out
new file mode 100644
index 0000000000..e8e07aed9d
--- /dev/null
+++ b/vlib/v/checker/tests/comptime_field_selector_not_in_for_err.out
@@ -0,0 +1,7 @@
+vlib/v/checker/tests/comptime_field_selector_not_in_for_err.vv:9:5: error: compile time field access can only be used when iterating over `T.fields`
+    7 |     mut t := T{}
+    8 |     name := 'test'
+    9 |     t.$name = '3'
+      |        ~~~~
+   10 | }
+   11 |
\ No newline at end of file
diff --git a/vlib/v/checker/tests/comptime_field_selector_not_in_for_err.vv b/vlib/v/checker/tests/comptime_field_selector_not_in_for_err.vv
new file mode 100644
index 0000000000..9f6dd63ba7
--- /dev/null
+++ b/vlib/v/checker/tests/comptime_field_selector_not_in_for_err.vv
@@ -0,0 +1,14 @@
+struct Foo {
+	test int
+	name string
+}
+
+fn test<T>() {
+	mut t := T{}
+	name := 'test'
+	t.$name = '3'
+}
+
+fn main() {
+	test<Foo>()
+}
diff --git a/vlib/v/checker/tests/comptime_field_selector_not_name_err.out b/vlib/v/checker/tests/comptime_field_selector_not_name_err.out
new file mode 100644
index 0000000000..2bedf135e0
--- /dev/null
+++ b/vlib/v/checker/tests/comptime_field_selector_not_name_err.out
@@ -0,0 +1,7 @@
+vlib/v/checker/tests/comptime_field_selector_not_name_err.vv:10:7: error: expected `string` instead of `FieldData` (e.g. `field.name`)
+    8 |     $for f in T.fields {
+    9 |         $if f.typ is string {
+   10 |             t.$f = '3'
+      |                ^
+   11 |         }
+   12 |     }
\ No newline at end of file
diff --git a/vlib/v/checker/tests/comptime_field_selector_not_name_err.vv b/vlib/v/checker/tests/comptime_field_selector_not_name_err.vv
new file mode 100644
index 0000000000..3683352fb5
--- /dev/null
+++ b/vlib/v/checker/tests/comptime_field_selector_not_name_err.vv
@@ -0,0 +1,17 @@
+struct Foo {
+	test int
+	name string
+}
+
+fn test<T>() {
+	mut t := T{}
+	$for f in T.fields {
+		$if f.typ is string {
+			t.$f = '3'
+		}
+	}
+}
+
+fn main() {
+	test<Foo>()
+}
diff --git a/vlib/v/fmt/fmt.v b/vlib/v/fmt/fmt.v
index 2f60d11f3b..6511669560 100644
--- a/vlib/v/fmt/fmt.v
+++ b/vlib/v/fmt/fmt.v
@@ -924,9 +924,18 @@ pub fn (mut f Fmt) expr(node ast.Expr) {
 					f.write("\$tmpl('$node.args_var')")
 				}
 			} else {
-				f.write('${node.left}.\$${node.method_name}($node.args_var)')
+				method_expr := if node.has_parens {
+					'(${node.method_name}($node.args_var))'
+				} else {
+					'${node.method_name}($node.args_var)'
+				}
+				f.write('${node.left}.$$method_expr')
 			}
 		}
+		ast.ComptimeSelector {
+			field_expr := if node.has_parens { '($node.field_expr)' } else { node.field_expr.str() }
+			f.write('${node.left}.$$field_expr')
+		}
 		ast.ConcatExpr {
 			for i, val in node.vals {
 				if i != 0 {
diff --git a/vlib/v/fmt/tests/comptime_field_selector_keep.vv b/vlib/v/fmt/tests/comptime_field_selector_keep.vv
new file mode 100644
index 0000000000..5d3e177da8
--- /dev/null
+++ b/vlib/v/fmt/tests/comptime_field_selector_keep.vv
@@ -0,0 +1,23 @@
+struct Foo {
+mut:
+	test string
+	name string
+}
+
+fn (f Foo) print() {
+	println('test')
+}
+
+fn test<T>() {
+	mut t := T{}
+	t.name = '2'
+	$for f in T.fields {
+		$if f.typ is string {
+			println(t.$f.name)
+		}
+	}
+}
+
+fn main() {
+	test<Foo>()
+}
diff --git a/vlib/v/fmt/tests/comptime_field_selector_parentheses_keep.vv b/vlib/v/fmt/tests/comptime_field_selector_parentheses_keep.vv
new file mode 100644
index 0000000000..e9752dee84
--- /dev/null
+++ b/vlib/v/fmt/tests/comptime_field_selector_parentheses_keep.vv
@@ -0,0 +1,23 @@
+struct Foo {
+mut:
+	test string
+	name string
+}
+
+fn (f Foo) print() {
+	println('test')
+}
+
+fn test<T>() {
+	mut t := T{}
+	t.name = '2'
+	$for f in T.fields {
+		$if f.typ is string {
+			println(t.$(f.name))
+		}
+	}
+}
+
+fn main() {
+	test<Foo>()
+}
diff --git a/vlib/v/gen/cgen.v b/vlib/v/gen/cgen.v
index 89c7819d78..86ee4aea52 100644
--- a/vlib/v/gen/cgen.v
+++ b/vlib/v/gen/cgen.v
@@ -109,7 +109,10 @@ mut:
 	inside_call                      bool
 	has_main                         bool
 	inside_const                     bool
-	comp_for_method                  string // $for method in T {
+	comp_for_method                  string      // $for method in T.methods {}
+	comp_for_field_var               string      // $for field in T.fields {}; the variable name
+	comp_for_field_value             table.Field // value of the field variable
+	comp_for_field_type              table.Type  // type of the field variable inferred from `$if field.typ is T {}`
 	comptime_var_type_map            map[string]table.Type
 	// tmp_arg_vars_to_free  []string
 	// autofree_pregen       map[string]string
@@ -2491,6 +2494,9 @@ fn (mut g Gen) expr(node ast.Expr) {
 		ast.ComptimeCall {
 			g.comptime_call(node)
 		}
+		ast.ComptimeSelector {
+			g.comptime_selector(node)
+		}
 		ast.Comment {}
 		ast.ConcatExpr {
 			g.concat_expr(node)
diff --git a/vlib/v/gen/comptime.v b/vlib/v/gen/comptime.v
index 2c02035bbf..944900e294 100644
--- a/vlib/v/gen/comptime.v
+++ b/vlib/v/gen/comptime.v
@@ -7,6 +7,26 @@ import v.ast
 import v.table
 import v.util
 
+fn (mut g Gen) comptime_selector(node ast.ComptimeSelector) {
+	g.expr(node.left)
+	if node.left_type.is_ptr() {
+		g.write('->')
+	} else {
+		g.write('.')
+	}
+	// check for field.name
+	if node.field_expr is ast.SelectorExpr {
+		if node.field_expr.expr is ast.Ident {
+			if node.field_expr.expr.name == g.comp_for_field_var &&
+				node.field_expr.field_name == 'name' {
+				g.write(g.comp_for_field_value.name)
+				return
+			}
+		}
+	}
+	g.expr(node.field_expr)
+}
+
 fn (mut g Gen) comptime_call(node ast.ComptimeCall) {
 	if node.is_vweb {
 		is_html := node.method_name == 'html'
@@ -314,17 +334,17 @@ fn (mut g Gen) comp_for(node ast.CompFor) {
 		}
 	} else if node.kind == .fields {
 		// TODO add fields
-		// TODO: temporary, remove this
-		sym_info := sym.info
-		if sym_info is table.Struct {
-			mut fields := sym_info.fields.filter(it.attrs.len == 0)
-			fields_with_attrs := sym_info.fields.filter(it.attrs.len > 0)
+		if sym.info is table.Struct {
+			mut fields := sym.info.fields.filter(it.attrs.len == 0)
+			fields_with_attrs := sym.info.fields.filter(it.attrs.len > 0)
 			fields << fields_with_attrs
 			if fields.len > 0 {
 				g.writeln('\tFieldData $node.val_var;')
 				g.writeln('\tmemset(&$node.val_var, 0, sizeof(FieldData));')
 			}
 			for field in fields {
+				g.comp_for_field_var = node.val_var
+				g.comp_for_field_value = field
 				g.writeln('\t// field $i')
 				g.writeln('\t${node.val_var}.name = _SLIT("$field.name");')
 				if field.attrs.len == 0 {
diff --git a/vlib/v/gen/js/js.v b/vlib/v/gen/js/js.v
index 924eb147d2..b8d29b7e33 100644
--- a/vlib/v/gen/js/js.v
+++ b/vlib/v/gen/js/js.v
@@ -573,6 +573,9 @@ fn (mut g JsGen) expr(node ast.Expr) {
 		ast.ComptimeCall {
 			// TODO
 		}
+		ast.ComptimeSelector {
+			// TODO
+		}
 		ast.UnsafeExpr {
 			g.expr(node.expr)
 		}
diff --git a/vlib/v/parser/comptime.v b/vlib/v/parser/comptime.v
index 507c3423aa..c5865c618b 100644
--- a/vlib/v/parser/comptime.v
+++ b/vlib/v/parser/comptime.v
@@ -263,53 +263,44 @@ fn os_from_string(os string) pref.OS {
 	return .linux
 }
 
-// `app.$action()` (`action` is a string)
-// `typ` is `App` in this example
-// fn (mut p Parser) comptime_method_call(typ table.Type) ast.ComptimeCall {
-fn (mut p Parser) comptime_method_call(left ast.Expr) ast.ComptimeCall {
+fn (mut p Parser) comptime_selector(left ast.Expr) ast.Expr {
 	p.check(.dollar)
-	method_name := p.check_name()
-	/*
-	mut j := 0
-	sym := p.table.get_type_symbol(typ)
-	if sym.kind != .struct_ {
-		p.error('not a struct')
+	mut has_parens := false
+	if p.tok.kind == .lpar {
+		p.check(.lpar)
+		has_parens = true
 	}
-	// info := sym.info as table.Struct
-	for method in sym.methods {
-		if method.return_type != table.void_type {
-			continue
+	if p.peek_tok.kind == .lpar {
+		method_name := p.check_name()
+		// `app.$action()` (`action` is a string)
+		if has_parens {
+			p.check(.rpar)
 		}
-		/*
-		receiver := method.args[0]
-		if !p.expr_var.ptr {
-			p.error('`$p.expr_var.name` needs to be a reference')
+		p.check(.lpar)
+		mut args_var := ''
+		if p.tok.kind == .name {
+			args_var = p.tok.lit
+			p.next()
 		}
-		amp := if receiver.is_mut && !p.expr_var.ptr { '&' } else { '' }
-		if j > 0 {
-			p.gen(' else ')
+		p.check(.rpar)
+		if p.tok.kind == .key_orelse {
+			p.check(.key_orelse)
+			p.check(.lcbr)
+		}
+		return ast.ComptimeCall{
+			has_parens: has_parens
+			left: left
+			method_name: method_name
+			args_var: args_var
 		}
-		p.genln('if (string_eq($method_name, _STR("$method.name")) ) ' + '${typ.name}_$method.name ($amp $p.expr_var.name);')
-		*/
-		j++
 	}
-	*/
-	p.check(.lpar)
-	mut args_var := ''
-	if p.tok.kind == .name {
-		args_var = p.tok.lit
-		p.next()
+	expr := p.expr(0)
+	if has_parens {
+		p.check(.rpar)
 	}
-	p.check(.rpar)
-	if p.tok.kind == .key_orelse {
-		p.check(.key_orelse)
-		// p.genln('else {')
-		p.check(.lcbr)
-		// p.statements()
-	}
-	return ast.ComptimeCall{
+	return ast.ComptimeSelector{
+		has_parens: has_parens
 		left: left
-		method_name: method_name
-		args_var: args_var
+		field_expr: expr
 	}
 }
diff --git a/vlib/v/parser/parser.v b/vlib/v/parser/parser.v
index 1d8239da08..d1cfd5e352 100644
--- a/vlib/v/parser/parser.v
+++ b/vlib/v/parser/parser.v
@@ -1413,7 +1413,7 @@ fn (mut p Parser) scope_register_ab() {
 fn (mut p Parser) dot_expr(left ast.Expr) ast.Expr {
 	p.next()
 	if p.tok.kind == .dollar {
-		return p.comptime_method_call(left)
+		return p.comptime_selector(left)
 	}
 	is_generic_call := p.is_generic_call()
 	name_pos := p.tok.position()
diff --git a/vlib/v/tests/comptime_field_selector_test.v b/vlib/v/tests/comptime_field_selector_test.v
new file mode 100644
index 0000000000..94fbc2ad95
--- /dev/null
+++ b/vlib/v/tests/comptime_field_selector_test.v
@@ -0,0 +1,62 @@
+struct Foo {
+	immutable int
+mut:
+	test string
+	name string
+}
+
+fn comptime_field_selector_read<T>() []string {
+	mut t := T{}
+	t.name = '2'
+	t.test = '1'
+	mut value_list := []string{}
+	$for f in T.fields {
+		$if f.typ is string {
+			value_list << t.$f.name
+		}
+	}
+	return value_list
+}
+
+fn test_comptime_field_selector_read() {
+	assert comptime_field_selector_read<Foo>() == ['1', '2']
+}
+
+fn comptime_field_selector_write<T>() T {
+	mut t := T{}
+	$for f in T.fields {
+		$if f.typ is string {
+			t.$f.name = '1'
+		}
+		$if f.typ is int {
+			t.$f.name = 1
+		}
+	}
+	return t
+}
+
+fn test_comptime_field_selector_write() {
+	res := comptime_field_selector_write<Foo>()
+	assert res.immutable == 1
+	assert res.test == '1'
+	assert res.name == '1'
+}
+
+struct Foo2 {
+	f Foo
+}
+
+fn nested_with_parentheses<T>() T {
+	mut t := T{}
+	$for f in T.fields {
+		$if f.typ is Foo {
+			t.$(f.name).test = '1'
+		}
+	}
+	return t
+}
+
+fn test_nested_with_parentheses() {
+	res := nested_with_parentheses<Foo2>()
+	assert res.f.test == '1'
+}