feat: Shorten "top", "right"... properties into "inset" property

CHANGELOG.md

@@ -43,6 +43,27 @@
     a,b{color:red}
     ```
 
+* Shorten `top`, `right`, `bottom`, `left` CSS property into `inset` when it is supported ([#1758](https://github.com/evanw/esbuild/pull/1758))
+
+    This release enables collapsing of `inset` related properties:
+
+    ```css
+    /* Original code */
+    div {
+      top: 0;
+      right: 0;
+      bottom: 0;
+      left: 0;
+    }
+
+    /* Output with "--minify-syntax" */
+    div {
+      inset: 0;
+    }
+    ```
+
+    This minification rule is only enabled when `inset` property is supported by the target environment. Make sure to set esbuild's `target` setting correctly when minifying if the code will be running in an older environment (e.g. earlier than Chrome 87).
+
 ## 0.13.12
 
 * Implement initial support for simplifying `calc()` expressions in CSS ([#1607](https://github.com/evanw/esbuild/issues/1607))

internal/compat/css_table.go

@@ -13,6 +13,8 @@ const (
 	// - rgb() can accept alpha values
 	// - Space-separated functional color notations
 	Modern_RGB_HSL
+
+	InsetProperty
 )
 
 func (features CSSFeature) Has(feature CSSFeature) bool {
@@ -42,6 +44,14 @@ var cssTable = map[CSSFeature]map[Engine][]int{
 		IOS:     {12, 2},
 		Safari:  {12, 1},
 	},
+	// Data from: https://developer.mozilla.org/en-US/docs/Web/CSS/inset
+	InsetProperty: {
+		Chrome:  {87},
+		Edge:    {87},
+		Firefox: {66},
+		IOS:     {14, 5},
+		Safari:  {14, 1},
+	},
 }
 
 // Return all features that are not available in at least one environment

internal/css_ast/css_decl_table.go

@@ -171,6 +171,7 @@ const (
 	DImageOrientation
 	DImageRendering
 	DInlineSize
+	DInset
 	DJustifyContent
 	DJustifyItems
 	DJustifySelf
@@ -489,6 +490,7 @@ var KnownDeclarations = map[string]D{
 	"image-orientation":           DImageOrientation,
 	"image-rendering":             DImageRendering,
 	"inline-size":                 DInlineSize,
+	"inset":                       DInset,
 	"justify-content":             DJustifyContent,
 	"justify-items":               DJustifyItems,
 	"justify-self":                DJustifySelf,

internal/css_parser/css_decls.go

@@ -1,6 +1,7 @@
 package css_parser
 
 import (
+	"github.com/evanw/esbuild/internal/compat"
 	"github.com/evanw/esbuild/internal/css_ast"
 	"github.com/evanw/esbuild/internal/css_lexer"
 )
@@ -77,8 +78,9 @@ func compactTokenQuad(a css_ast.Token, b css_ast.Token, c css_ast.Token, d css_a
 }
 
 func (p *parser) processDeclarations(rules []css_ast.Rule) []css_ast.Rule {
-	margin := boxTracker{}
-	padding := boxTracker{}
+	margin := newBoxTracker(css_ast.DMargin, "margin", true)
+	padding := newBoxTracker(css_ast.DPadding, "padding", false)
+	inset := newBoxTracker(css_ast.DInset, "inset", true)
 	borderRadius := borderRadiusTracker{}
 
 	for i, rule := range rules {
@@ -131,6 +133,27 @@ func (p *parser) processDeclarations(rules []css_ast.Rule) []css_ast.Rule {
 				decl.Value = p.mangleBoxShadows(decl.Value)
 			}
 
+		case css_ast.DMargin:
+			if p.options.MangleSyntax {
+				margin.mangleSides(rules, decl, i, p.options.RemoveWhitespace)
+			}
+		case css_ast.DMarginTop:
+			if p.options.MangleSyntax {
+				margin.mangleSide(rules, decl, i, p.options.RemoveWhitespace, boxTop)
+			}
+		case css_ast.DMarginRight:
+			if p.options.MangleSyntax {
+				margin.mangleSide(rules, decl, i, p.options.RemoveWhitespace, boxRight)
+			}
+		case css_ast.DMarginBottom:
+			if p.options.MangleSyntax {
+				margin.mangleSide(rules, decl, i, p.options.RemoveWhitespace, boxBottom)
+			}
+		case css_ast.DMarginLeft:
+			if p.options.MangleSyntax {
+				margin.mangleSide(rules, decl, i, p.options.RemoveWhitespace, boxLeft)
+			}
+
 		case css_ast.DPadding:
 			if p.options.MangleSyntax {
 				padding.mangleSides(rules, decl, i, p.options.RemoveWhitespace)
@@ -152,25 +175,25 @@ func (p *parser) processDeclarations(rules []css_ast.Rule) []css_ast.Rule {
 				padding.mangleSide(rules, decl, i, p.options.RemoveWhitespace, boxLeft)
 			}
 
-		case css_ast.DMargin:
-			if p.options.MangleSyntax {
-				margin.mangleSides(rules, decl, i, p.options.RemoveWhitespace)
+		case css_ast.DInset:
+			if !p.options.UnsupportedCSSFeatures.Has(compat.InsetProperty) && p.options.MangleSyntax {
+				inset.mangleSides(rules, decl, i, p.options.RemoveWhitespace)
 			}
-		case css_ast.DMarginTop:
-			if p.options.MangleSyntax {
-				margin.mangleSide(rules, decl, i, p.options.RemoveWhitespace, boxTop)
+		case css_ast.DTop:
+			if !p.options.UnsupportedCSSFeatures.Has(compat.InsetProperty) && p.options.MangleSyntax {
+				inset.mangleSide(rules, decl, i, p.options.RemoveWhitespace, boxTop)
 			}
-		case css_ast.DMarginRight:
-			if p.options.MangleSyntax {
-				margin.mangleSide(rules, decl, i, p.options.RemoveWhitespace, boxRight)
+		case css_ast.DRight:
+			if !p.options.UnsupportedCSSFeatures.Has(compat.InsetProperty) && p.options.MangleSyntax {
+				inset.mangleSide(rules, decl, i, p.options.RemoveWhitespace, boxRight)
 			}
-		case css_ast.DMarginBottom:
-			if p.options.MangleSyntax {
-				margin.mangleSide(rules, decl, i, p.options.RemoveWhitespace, boxBottom)
+		case css_ast.DBottom:
+			if !p.options.UnsupportedCSSFeatures.Has(compat.InsetProperty) && p.options.MangleSyntax {
+				inset.mangleSide(rules, decl, i, p.options.RemoveWhitespace, boxBottom)
 			}
-		case css_ast.DMarginLeft:
-			if p.options.MangleSyntax {
-				margin.mangleSide(rules, decl, i, p.options.RemoveWhitespace, boxLeft)
+		case css_ast.DLeft:
+			if !p.options.UnsupportedCSSFeatures.Has(compat.InsetProperty) && p.options.MangleSyntax {
+				inset.mangleSide(rules, decl, i, p.options.RemoveWhitespace, boxLeft)
 			}
 
 		case css_ast.DBorderRadius:

internal/css_parser/css_decls_box.go

@@ -20,10 +20,22 @@ type boxSide struct {
 }
 
 type boxTracker struct {
+	key       css_ast.D
+	keyText   string
+	allowAuto bool
+
 	sides     [4]boxSide
 	important bool
 }
 
+func newBoxTracker(key css_ast.D, keyText string, allowAuto bool) boxTracker {
+	return boxTracker{
+		key:       key,
+		keyText:   keyText,
+		allowAuto: allowAuto,
+	}
+}
+
 func (box *boxTracker) updateSide(rules []css_ast.Rule, side int, new boxSide) {
 	if old := box.sides[side]; old.token.Kind != css_lexer.TEndOfFile && (!new.single || old.single) {
 		rules[old.index] = css_ast.Rule{}
@@ -39,16 +51,15 @@ func (box *boxTracker) mangleSides(rules []css_ast.Rule, decl *css_ast.RDeclarat
 	}
 
 	allowedIdent := ""
-	isMargin := decl.Key == css_ast.DMargin
-	if isMargin {
+	if box.allowAuto {
 		allowedIdent = "auto"
 	}
 	if quad, ok := expandTokenQuad(decl.Value, allowedIdent); ok {
 		for side, t := range quad {
 			t.TurnLengthIntoNumberIfZero()
 			box.updateSide(rules, side, boxSide{token: t, index: uint32(index)})
 		}
-		box.compactRules(rules, decl.KeyRange, removeWhitespace, isMargin)
+		box.compactRules(rules, decl.KeyRange, removeWhitespace)
 	} else {
 		box.sides = [4]boxSide{}
 	}
@@ -61,27 +72,21 @@ func (box *boxTracker) mangleSide(rules []css_ast.Rule, decl *css_ast.RDeclarati
 		box.important = decl.Important
 	}
 
-	isMargin := false
-	switch decl.Key {
-	case css_ast.DMarginTop, css_ast.DMarginRight, css_ast.DMarginBottom, css_ast.DMarginLeft:
-		isMargin = true
-	}
-
 	if tokens := decl.Value; len(tokens) == 1 {
-		if t := tokens[0]; t.Kind.IsNumeric() || (t.Kind == css_lexer.TIdent && isMargin && t.Text == "auto") {
+		if t := tokens[0]; t.Kind.IsNumeric() || (t.Kind == css_lexer.TIdent && box.allowAuto && t.Text == "auto") {
 			if t.TurnLengthIntoNumberIfZero() {
 				tokens[0] = t
 			}
 			box.updateSide(rules, side, boxSide{token: t, index: uint32(index), single: true})
-			box.compactRules(rules, decl.KeyRange, removeWhitespace, isMargin)
+			box.compactRules(rules, decl.KeyRange, removeWhitespace)
 			return
 		}
 	}
 
 	box.sides = [4]boxSide{}
 }
 
-func (box *boxTracker) compactRules(rules []css_ast.Rule, keyRange logger.Range, removeWhitespace bool, isMargin bool) {
+func (box *boxTracker) compactRules(rules []css_ast.Rule, keyRange logger.Range, removeWhitespace bool) {
 	// All tokens must be present
 	if eof := css_lexer.TEndOfFile; box.sides[0].token.Kind == eof || box.sides[1].token.Kind == eof ||
 		box.sides[2].token.Kind == eof || box.sides[3].token.Kind == eof {
@@ -104,18 +109,9 @@ func (box *boxTracker) compactRules(rules []css_ast.Rule, keyRange logger.Range,
 	rules[box.sides[3].index] = css_ast.Rule{}
 
 	// Insert the combined declaration where the last rule was
-	var key css_ast.D
-	var keyText string
-	if isMargin {
-		key = css_ast.DMargin
-		keyText = "margin"
-	} else {
-		key = css_ast.DPadding
-		keyText = "padding"
-	}
 	rules[box.sides[3].index].Data = &css_ast.RDeclaration{
-		Key:       key,
-		KeyText:   keyText,
+		Key:       box.key,
+		KeyText:   box.keyText,
 		Value:     tokens,
 		KeyRange:  keyRange,
 		Important: box.important,