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js_parser_lower.go
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js_parser_lower.go
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// This file contains code for "lowering" syntax, which means converting it to
// older JavaScript. For example, "a ** b" becomes a call to "Math.pow(a, b)"
// when lowered. Which syntax is lowered is determined by the language target.
package js_parser
import (
"fmt"
"github.com/evanw/esbuild/internal/compat"
"github.com/evanw/esbuild/internal/config"
"github.com/evanw/esbuild/internal/js_ast"
"github.com/evanw/esbuild/internal/js_lexer"
"github.com/evanw/esbuild/internal/logger"
)
func (p *parser) markSyntaxFeature(feature compat.JSFeature, r logger.Range) (didGenerateError bool) {
didGenerateError = true
if !p.options.unsupportedJSFeatures.Has(feature) {
if feature == compat.TopLevelAwait && !p.options.outputFormat.KeepES6ImportExportSyntax() {
p.log.AddRangeError(&p.tracker, r, fmt.Sprintf(
"Top-level await is currently not supported with the %q output format", p.options.outputFormat.String()))
return
}
didGenerateError = false
return
}
var name string
var notes []logger.MsgData
where := "the configured target environment"
if tsTarget := p.options.tsTarget; tsTarget != nil && tsTarget.UnsupportedJSFeatures.Has(feature) {
tracker := logger.MakeLineColumnTracker(&tsTarget.Source)
where = fmt.Sprintf("%s (%q)", where, tsTarget.Target)
notes = []logger.MsgData{logger.RangeData(&tracker, tsTarget.Range, fmt.Sprintf(
"The target environment was set to %q here", tsTarget.Target))}
} else if p.options.originalTargetEnv != "" {
where = fmt.Sprintf("%s (%s)", where, p.options.originalTargetEnv)
}
switch feature {
case compat.DefaultArgument:
name = "default arguments"
case compat.RestArgument:
name = "rest arguments"
case compat.ArraySpread:
name = "array spread"
case compat.ForOf:
name = "for-of loops"
case compat.ObjectAccessors:
name = "object accessors"
case compat.ObjectExtensions:
name = "object literal extensions"
case compat.Destructuring:
name = "destructuring"
case compat.NewTarget:
name = "new.target"
case compat.Const:
name = "const"
case compat.Let:
name = "let"
case compat.Class:
name = "class syntax"
case compat.Generator:
name = "generator functions"
case compat.AsyncAwait:
name = "async functions"
case compat.AsyncGenerator:
name = "async generator functions"
case compat.ForAwait:
name = "for-await loops"
case compat.NestedRestBinding:
name = "non-identifier array rest patterns"
case compat.ImportAssertions:
p.log.AddRangeErrorWithNotes(&p.tracker, r, fmt.Sprintf(
"Using an arbitrary value as the second argument to \"import()\" is not possible in %s", where), notes)
return
case compat.TopLevelAwait:
p.log.AddRangeErrorWithNotes(&p.tracker, r, fmt.Sprintf(
"Top-level await is not available in %s", where), notes)
return
case compat.ArbitraryModuleNamespaceNames:
p.log.AddRangeErrorWithNotes(&p.tracker, r, fmt.Sprintf(
"Using a string as a module namespace identifier name is not supported in %s", where), notes)
return
case compat.BigInt:
// Transforming these will never be supported
p.log.AddRangeErrorWithNotes(&p.tracker, r, fmt.Sprintf(
"Big integer literals are not available in %s", where), notes)
return
case compat.ImportMeta:
// This can't be polyfilled
p.log.AddRangeWarningWithNotes(&p.tracker, r, fmt.Sprintf(
"\"import.meta\" is not available in %s and will be empty", where), notes)
return
default:
p.log.AddRangeErrorWithNotes(&p.tracker, r, fmt.Sprintf(
"This feature is not available in %s", where), notes)
return
}
p.log.AddRangeErrorWithNotes(&p.tracker, r, fmt.Sprintf(
"Transforming %s to %s is not supported yet", name, where), notes)
return
}
func (p *parser) isStrictMode() bool {
return p.currentScope.StrictMode != js_ast.SloppyMode
}
func (p *parser) isStrictModeOutputFormat() bool {
return p.options.outputFormat == config.FormatESModule
}
type strictModeFeature uint8
const (
withStatement strictModeFeature = iota
deleteBareName
forInVarInit
evalOrArguments
reservedWord
legacyOctalLiteral
legacyOctalEscape
ifElseFunctionStmt
)
func (p *parser) markStrictModeFeature(feature strictModeFeature, r logger.Range, detail string) {
var text string
canBeTransformed := false
switch feature {
case withStatement:
text = "With statements"
case deleteBareName:
text = "Delete of a bare identifier"
case forInVarInit:
text = "Variable initializers inside for-in loops"
canBeTransformed = true
case evalOrArguments:
text = fmt.Sprintf("Declarations with the name %q", detail)
case reservedWord:
text = fmt.Sprintf("%q is a reserved word and", detail)
case legacyOctalLiteral:
text = "Legacy octal literals"
case legacyOctalEscape:
text = "Legacy octal escape sequences"
case ifElseFunctionStmt:
text = "Function declarations inside if statements"
default:
text = "This feature"
}
if p.isStrictMode() {
var why string
var notes []logger.MsgData
var where logger.Range
switch p.currentScope.StrictMode {
case js_ast.ImplicitStrictModeImport:
where = p.es6ImportKeyword
case js_ast.ImplicitStrictModeExport:
where = p.es6ExportKeyword
case js_ast.ImplicitStrictModeTopLevelAwait:
where = p.topLevelAwaitKeyword
case js_ast.ImplicitStrictModeClass:
why = "All code inside a class is implicitly in strict mode"
where = p.enclosingClassKeyword
case js_ast.ExplicitStrictMode:
why = "Strict mode is triggered by the \"use strict\" directive here"
where = p.source.RangeOfString(p.currentScope.UseStrictLoc)
}
if where.Len > 0 {
if why == "" {
why = fmt.Sprintf("This file is implicitly in strict mode because of the %q keyword here", p.source.TextForRange(where))
}
notes = []logger.MsgData{logger.RangeData(&p.tracker, where, why)}
}
p.log.AddRangeErrorWithNotes(&p.tracker, r,
fmt.Sprintf("%s cannot be used in strict mode", text), notes)
} else if !canBeTransformed && p.isStrictModeOutputFormat() {
p.log.AddRangeError(&p.tracker, r,
fmt.Sprintf("%s cannot be used with the \"esm\" output format due to strict mode", text))
}
}
// Mark the feature if "loweredFeature" is unsupported. This is used when one
// feature is implemented in terms of another feature.
func (p *parser) markLoweredSyntaxFeature(feature compat.JSFeature, r logger.Range, loweredFeature compat.JSFeature) {
if p.options.unsupportedJSFeatures.Has(loweredFeature) {
p.markSyntaxFeature(feature, r)
}
}
func (p *parser) privateSymbolNeedsToBeLowered(private *js_ast.EPrivateIdentifier) bool {
symbol := &p.symbols[private.Ref.InnerIndex]
return p.options.unsupportedJSFeatures.Has(symbol.Kind.Feature()) || symbol.PrivateSymbolMustBeLowered
}
func (p *parser) captureThis() js_ast.Ref {
if p.fnOnlyDataVisit.thisCaptureRef == nil {
ref := p.newSymbol(js_ast.SymbolHoisted, "_this")
p.fnOnlyDataVisit.thisCaptureRef = &ref
}
return *p.fnOnlyDataVisit.thisCaptureRef
}
func (p *parser) captureArguments() js_ast.Ref {
if p.fnOnlyDataVisit.argumentsCaptureRef == nil {
ref := p.newSymbol(js_ast.SymbolHoisted, "_arguments")
p.fnOnlyDataVisit.argumentsCaptureRef = &ref
}
return *p.fnOnlyDataVisit.argumentsCaptureRef
}
func (p *parser) lowerFunction(
isAsync *bool,
args *[]js_ast.Arg,
bodyLoc logger.Loc,
bodyStmts *[]js_ast.Stmt,
preferExpr *bool,
hasRestArg *bool,
isArrow bool,
) {
// Lower object rest binding patterns in function arguments
if p.options.unsupportedJSFeatures.Has(compat.ObjectRestSpread) {
var prefixStmts []js_ast.Stmt
// Lower each argument individually instead of lowering all arguments
// together. There is a correctness tradeoff here around default values
// for function arguments, with no right answer.
//
// Lowering all arguments together will preserve the order of side effects
// for default values, but will mess up their scope:
//
// // Side effect order: a(), b(), c()
// function foo([{[a()]: w, ...x}, y = b()], z = c()) {}
//
// // Side effect order is correct but scope is wrong
// function foo(_a, _b) {
// var [[{[a()]: w, ...x}, y = b()], z = c()] = [_a, _b]
// }
//
// Lowering each argument individually will preserve the scope for default
// values that don't contain object rest binding patterns, but will mess up
// the side effect order:
//
// // Side effect order: a(), b(), c()
// function foo([{[a()]: w, ...x}, y = b()], z = c()) {}
//
// // Side effect order is wrong but scope for c() is correct
// function foo(_a, z = c()) {
// var [{[a()]: w, ...x}, y = b()] = _a
// }
//
// This transform chooses to lower each argument individually with the
// thinking that perhaps scope matters more in real-world code than side
// effect order.
for i, arg := range *args {
if bindingHasObjectRest(arg.Binding) {
ref := p.generateTempRef(tempRefNoDeclare, "")
target := js_ast.ConvertBindingToExpr(arg.Binding, nil)
init := js_ast.Expr{Loc: arg.Binding.Loc, Data: &js_ast.EIdentifier{Ref: ref}}
p.recordUsage(ref)
if decls, ok := p.lowerObjectRestToDecls(target, init, nil); ok {
// Replace the binding but leave the default value intact
(*args)[i].Binding.Data = &js_ast.BIdentifier{Ref: ref}
// Append a variable declaration to the function body
prefixStmts = append(prefixStmts, js_ast.Stmt{Loc: arg.Binding.Loc,
Data: &js_ast.SLocal{Kind: js_ast.LocalVar, Decls: decls}})
}
}
}
if len(prefixStmts) > 0 {
*bodyStmts = append(prefixStmts, *bodyStmts...)
}
}
// Lower async functions
if p.options.unsupportedJSFeatures.Has(compat.AsyncAwait) && *isAsync {
// Use the shortened form if we're an arrow function
if preferExpr != nil {
*preferExpr = true
}
// Determine the value for "this"
thisValue, hasThisValue := p.valueForThis(bodyLoc, false /* shouldWarn */)
if !hasThisValue {
thisValue = js_ast.Expr{Loc: bodyLoc, Data: js_ast.EThisShared}
}
// Move the code into a nested generator function
fn := js_ast.Fn{
IsGenerator: true,
Body: js_ast.FnBody{Loc: bodyLoc, Stmts: *bodyStmts},
}
*bodyStmts = nil
// Errors thrown during argument evaluation must reject the
// resulting promise, which needs more complex code to handle
couldThrowErrors := false
for _, arg := range *args {
if _, ok := arg.Binding.Data.(*js_ast.BIdentifier); !ok ||
(arg.DefaultOrNil.Data != nil && couldPotentiallyThrow(arg.DefaultOrNil.Data)) {
couldThrowErrors = true
break
}
}
// Forward the arguments to the wrapper function
usesArgumentsRef := !isArrow && p.fnOnlyDataVisit.argumentsRef != nil &&
p.symbolUses[*p.fnOnlyDataVisit.argumentsRef].CountEstimate > 0
var forwardedArgs js_ast.Expr
if !couldThrowErrors && !usesArgumentsRef {
// Simple case: the arguments can stay on the outer function. It's
// worth separating out the simple case because it's the common case
// and it generates smaller code.
forwardedArgs = js_ast.Expr{Loc: bodyLoc, Data: js_ast.ENullShared}
} else {
// If code uses "arguments" then we must move the arguments to the inner
// function. This is because you can modify arguments by assigning to
// elements in the "arguments" object:
//
// async function foo(x) {
// arguments[0] = 1;
// // "x" must be 1 here
// }
//
// Complex case: the arguments must be moved to the inner function
fn.Args = *args
fn.HasRestArg = *hasRestArg
*args = nil
*hasRestArg = false
// Make sure to not change the value of the "length" property. This is
// done by generating dummy arguments for the outer function equal to
// the expected length of the function:
//
// async function foo(a, b, c = d, ...e) {
// }
//
// This turns into:
//
// function foo(_0, _1) {
// return __async(this, arguments, function* (a, b, c = d, ...e) {
// });
// }
//
// The "_0" and "_1" are dummy variables to ensure "foo.length" is 2.
for i, arg := range fn.Args {
if arg.DefaultOrNil.Data != nil || fn.HasRestArg && i+1 == len(fn.Args) {
// Arguments from here on don't add to the "length"
break
}
// Generate a dummy variable
argRef := p.newSymbol(js_ast.SymbolOther, fmt.Sprintf("_%d", i))
p.currentScope.Generated = append(p.currentScope.Generated, argRef)
*args = append(*args, js_ast.Arg{Binding: js_ast.Binding{Loc: arg.Binding.Loc, Data: &js_ast.BIdentifier{Ref: argRef}}})
}
// Forward all arguments from the outer function to the inner function
if !isArrow {
// Normal functions can just use "arguments" to forward everything
forwardedArgs = js_ast.Expr{Loc: bodyLoc, Data: &js_ast.EIdentifier{Ref: *p.fnOnlyDataVisit.argumentsRef}}
} else {
// Arrow functions can't use "arguments", so we need to forward
// the arguments manually.
//
// Note that if the arrow function references "arguments" in its body
// (even if it's inside another nested arrow function), that reference
// to "arguments" will have to be subsituted with a captured variable.
// This is because we're changing the arrow function into a generator
// function, which introduces a variable named "arguments". This is
// handled separately during symbol resolution instead of being handled
// here so we don't need to re-traverse the arrow function body.
// If we need to forward more than the current number of arguments,
// add a rest argument to the set of forwarding variables. This is the
// case if the arrow function has rest or default arguments.
if len(*args) < len(fn.Args) {
argRef := p.newSymbol(js_ast.SymbolOther, fmt.Sprintf("_%d", len(*args)))
p.currentScope.Generated = append(p.currentScope.Generated, argRef)
*args = append(*args, js_ast.Arg{Binding: js_ast.Binding{Loc: bodyLoc, Data: &js_ast.BIdentifier{Ref: argRef}}})
*hasRestArg = true
}
// Forward all of the arguments
items := make([]js_ast.Expr, 0, len(*args))
for i, arg := range *args {
id := arg.Binding.Data.(*js_ast.BIdentifier)
item := js_ast.Expr{Loc: arg.Binding.Loc, Data: &js_ast.EIdentifier{Ref: id.Ref}}
if *hasRestArg && i+1 == len(*args) {
item.Data = &js_ast.ESpread{Value: item}
}
items = append(items, item)
}
forwardedArgs = js_ast.Expr{Loc: bodyLoc, Data: &js_ast.EArray{Items: items, IsSingleLine: true}}
}
}
// "async function foo(a, b) { stmts }" => "function foo(a, b) { return __async(this, null, function* () { stmts }) }"
*isAsync = false
callAsync := p.callRuntime(bodyLoc, "__async", []js_ast.Expr{
thisValue,
forwardedArgs,
{Loc: bodyLoc, Data: &js_ast.EFunction{Fn: fn}},
})
returnStmt := js_ast.Stmt{Loc: bodyLoc, Data: &js_ast.SReturn{ValueOrNil: callAsync}}
// Prepend the "super" index function if necessary
if p.fnOrArrowDataVisit.superIndexRef != nil {
argRef := p.newSymbol(js_ast.SymbolOther, "key")
p.currentScope.Generated = append(p.currentScope.Generated, *p.fnOrArrowDataVisit.superIndexRef, argRef)
superIndexStmt := js_ast.Stmt{Loc: bodyLoc, Data: &js_ast.SLocal{
Decls: []js_ast.Decl{{
Binding: js_ast.Binding{Loc: bodyLoc, Data: &js_ast.BIdentifier{Ref: *p.fnOrArrowDataVisit.superIndexRef}},
ValueOrNil: js_ast.Expr{Loc: bodyLoc, Data: &js_ast.EArrow{
Args: []js_ast.Arg{{
Binding: js_ast.Binding{Loc: bodyLoc, Data: &js_ast.BIdentifier{Ref: argRef}},
}},
Body: js_ast.FnBody{
Loc: bodyLoc,
Stmts: []js_ast.Stmt{{Loc: bodyLoc, Data: &js_ast.SReturn{
ValueOrNil: js_ast.Expr{Loc: bodyLoc, Data: &js_ast.EIndex{
Target: js_ast.Expr{Loc: bodyLoc, Data: js_ast.ESuperShared},
Index: js_ast.Expr{Loc: bodyLoc, Data: &js_ast.EIdentifier{Ref: argRef}},
}},
}}},
},
PreferExpr: true,
}},
}},
}}
p.recordUsage(argRef)
*bodyStmts = []js_ast.Stmt{superIndexStmt, returnStmt}
} else {
*bodyStmts = []js_ast.Stmt{returnStmt}
}
}
}
func (p *parser) lowerOptionalChain(expr js_ast.Expr, in exprIn, childOut exprOut) (js_ast.Expr, exprOut) {
valueWhenUndefined := js_ast.Expr{Loc: expr.Loc, Data: js_ast.EUndefinedShared}
endsWithPropertyAccess := false
containsPrivateName := false
startsWithCall := false
originalExpr := expr
chain := []js_ast.Expr{}
loc := expr.Loc
// Step 1: Get an array of all expressions in the chain. We're traversing the
// chain from the outside in, so the array will be filled in "backwards".
flatten:
for {
chain = append(chain, expr)
switch e := expr.Data.(type) {
case *js_ast.EDot:
expr = e.Target
if len(chain) == 1 {
endsWithPropertyAccess = true
}
if e.OptionalChain == js_ast.OptionalChainStart {
break flatten
}
case *js_ast.EIndex:
expr = e.Target
if len(chain) == 1 {
endsWithPropertyAccess = true
}
// If this is a private name that needs to be lowered, the entire chain
// itself will have to be lowered even if the language target supports
// optional chaining. This is because there's no way to use our shim
// function for private names with optional chaining syntax.
if private, ok := e.Index.Data.(*js_ast.EPrivateIdentifier); ok && p.privateSymbolNeedsToBeLowered(private) {
containsPrivateName = true
}
if e.OptionalChain == js_ast.OptionalChainStart {
break flatten
}
case *js_ast.ECall:
expr = e.Target
if e.OptionalChain == js_ast.OptionalChainStart {
startsWithCall = true
break flatten
}
case *js_ast.EUnary: // UnOpDelete
valueWhenUndefined = js_ast.Expr{Loc: loc, Data: &js_ast.EBoolean{Value: true}}
expr = e.Value
default:
panic("Internal error")
}
}
// Stop now if we can strip the whole chain as dead code. Since the chain is
// lazily evaluated, it's safe to just drop the code entirely.
if p.options.mangleSyntax {
if isNullOrUndefined, sideEffects, ok := toNullOrUndefinedWithSideEffects(expr.Data); ok && isNullOrUndefined {
if sideEffects == couldHaveSideEffects {
return js_ast.JoinWithComma(p.simplifyUnusedExpr(expr), valueWhenUndefined), exprOut{}
}
return valueWhenUndefined, exprOut{}
}
} else {
switch expr.Data.(type) {
case *js_ast.ENull, *js_ast.EUndefined:
return valueWhenUndefined, exprOut{}
}
}
// We need to lower this if this is an optional call off of a private name
// such as "foo.#bar?.()" because the value of "this" must be captured.
if _, _, private := p.extractPrivateIndex(expr); private != nil {
containsPrivateName = true
}
// Don't lower this if we don't need to. This check must be done here instead
// of earlier so we can do the dead code elimination above when the target is
// null or undefined.
if !p.options.unsupportedJSFeatures.Has(compat.OptionalChain) && !containsPrivateName {
return originalExpr, exprOut{}
}
// Step 2: Figure out if we need to capture the value for "this" for the
// initial ECall. This will be passed to ".call(this, ...args)" later.
var thisArg js_ast.Expr
var targetWrapFunc func(js_ast.Expr) js_ast.Expr
if startsWithCall {
if childOut.thisArgFunc != nil {
// The initial value is a nested optional chain that ended in a property
// access. The nested chain was processed first and has saved the
// appropriate value for "this". The callback here will return a
// reference to that saved location.
thisArg = childOut.thisArgFunc()
} else {
// The initial value is a normal expression. If it's a property access,
// strip the property off and save the target of the property access to
// be used as the value for "this".
switch e := expr.Data.(type) {
case *js_ast.EDot:
if _, ok := e.Target.Data.(*js_ast.ESuper); ok {
// Lower "super.prop" if necessary
if p.shouldLowerSuperPropertyAccess(e.Target) {
key := js_ast.Expr{Loc: e.NameLoc, Data: &js_ast.EString{Value: js_lexer.StringToUTF16(e.Name)}}
expr = p.lowerSuperPropertyAccess(expr.Loc, key)
}
// Special-case "super.foo?.()" to avoid a syntax error. Without this,
// we would generate:
//
// (_b = (_a = super).foo) == null ? void 0 : _b.call(_a)
//
// which is a syntax error. Now we generate this instead:
//
// (_a = super.foo) == null ? void 0 : _a.call(this)
//
thisArg = js_ast.Expr{Loc: loc, Data: js_ast.EThisShared}
} else {
targetFunc, wrapFunc := p.captureValueWithPossibleSideEffects(loc, 2, e.Target, valueDefinitelyNotMutated)
expr = js_ast.Expr{Loc: loc, Data: &js_ast.EDot{
Target: targetFunc(),
Name: e.Name,
NameLoc: e.NameLoc,
}}
thisArg = targetFunc()
targetWrapFunc = wrapFunc
}
case *js_ast.EIndex:
if _, ok := e.Target.Data.(*js_ast.ESuper); ok {
// Lower "super[prop]" if necessary
if p.shouldLowerSuperPropertyAccess(e.Target) {
expr = p.lowerSuperPropertyAccess(expr.Loc, e.Index)
}
// See the comment above about a similar special case for EDot
thisArg = js_ast.Expr{Loc: loc, Data: js_ast.EThisShared}
} else {
targetFunc, wrapFunc := p.captureValueWithPossibleSideEffects(loc, 2, e.Target, valueDefinitelyNotMutated)
targetWrapFunc = wrapFunc
// Capture the value of "this" if the target of the starting call
// expression is a private property access
if private, ok := e.Index.Data.(*js_ast.EPrivateIdentifier); ok && p.privateSymbolNeedsToBeLowered(private) {
// "foo().#bar?.()" must capture "foo()" for "this"
expr = p.lowerPrivateGet(targetFunc(), e.Index.Loc, private)
thisArg = targetFunc()
break
}
expr = js_ast.Expr{Loc: loc, Data: &js_ast.EIndex{
Target: targetFunc(),
Index: e.Index,
}}
thisArg = targetFunc()
}
}
}
}
// Step 3: Figure out if we need to capture the starting value. We don't need
// to capture it if it doesn't have any side effects (e.g. it's just a bare
// identifier). Skipping the capture reduces code size and matches the output
// of the TypeScript compiler.
exprFunc, exprWrapFunc := p.captureValueWithPossibleSideEffects(loc, 2, expr, valueDefinitelyNotMutated)
expr = exprFunc()
result := exprFunc()
// Step 4: Wrap the starting value by each expression in the chain. We
// traverse the chain in reverse because we want to go from the inside out
// and the chain was built from the outside in.
var parentThisArgFunc func() js_ast.Expr
var parentThisArgWrapFunc func(js_ast.Expr) js_ast.Expr
var privateThisFunc func() js_ast.Expr
var privateThisWrapFunc func(js_ast.Expr) js_ast.Expr
for i := len(chain) - 1; i >= 0; i-- {
// Save a reference to the value of "this" for our parent ECall
if i == 0 && in.storeThisArgForParentOptionalChain && endsWithPropertyAccess {
parentThisArgFunc, parentThisArgWrapFunc = p.captureValueWithPossibleSideEffects(result.Loc, 2, result, valueDefinitelyNotMutated)
result = parentThisArgFunc()
}
switch e := chain[i].Data.(type) {
case *js_ast.EDot:
result = js_ast.Expr{Loc: loc, Data: &js_ast.EDot{
Target: result,
Name: e.Name,
NameLoc: e.NameLoc,
}}
case *js_ast.EIndex:
if private, ok := e.Index.Data.(*js_ast.EPrivateIdentifier); ok && p.privateSymbolNeedsToBeLowered(private) {
// If this is private name property access inside a call expression and
// the call expression is part of this chain, then the call expression
// is going to need a copy of the property access target as the value
// for "this" for the call. Example for this case: "foo.#bar?.()"
if i > 0 {
if _, ok := chain[i-1].Data.(*js_ast.ECall); ok {
privateThisFunc, privateThisWrapFunc = p.captureValueWithPossibleSideEffects(loc, 2, result, valueDefinitelyNotMutated)
result = privateThisFunc()
}
}
result = p.lowerPrivateGet(result, e.Index.Loc, private)
continue
}
result = js_ast.Expr{Loc: loc, Data: &js_ast.EIndex{
Target: result,
Index: e.Index,
}}
case *js_ast.ECall:
// If this is the initial ECall in the chain and it's being called off of
// a property access, invoke the function using ".call(this, ...args)" to
// explicitly provide the value for "this".
if i == len(chain)-1 && thisArg.Data != nil {
result = js_ast.Expr{Loc: loc, Data: &js_ast.ECall{
Target: js_ast.Expr{Loc: loc, Data: &js_ast.EDot{
Target: result,
Name: "call",
NameLoc: loc,
}},
Args: append([]js_ast.Expr{thisArg}, e.Args...),
CanBeUnwrappedIfUnused: e.CanBeUnwrappedIfUnused,
}}
break
}
// If the target of this call expression is a private name property
// access that's also part of this chain, then we must use the copy of
// the property access target that was stashed away earlier as the value
// for "this" for the call. Example for this case: "foo.#bar?.()"
if privateThisFunc != nil {
result = privateThisWrapFunc(js_ast.Expr{Loc: loc, Data: &js_ast.ECall{
Target: js_ast.Expr{Loc: loc, Data: &js_ast.EDot{
Target: result,
Name: "call",
NameLoc: loc,
}},
Args: append([]js_ast.Expr{privateThisFunc()}, e.Args...),
CanBeUnwrappedIfUnused: e.CanBeUnwrappedIfUnused,
}})
privateThisFunc = nil
break
}
result = js_ast.Expr{Loc: loc, Data: &js_ast.ECall{
Target: result,
Args: e.Args,
CanBeUnwrappedIfUnused: e.CanBeUnwrappedIfUnused,
}}
case *js_ast.EUnary:
result = js_ast.Expr{Loc: loc, Data: &js_ast.EUnary{
Op: js_ast.UnOpDelete,
Value: result,
}}
default:
panic("Internal error")
}
}
// Step 5: Wrap it all in a conditional that returns the chain or the default
// value if the initial value is null/undefined. The default value is usually
// "undefined" but is "true" if the chain ends in a "delete" operator.
// "x?.y" => "x == null ? void 0 : x.y"
// "x()?.y()" => "(_a = x()) == null ? void 0 : _a.y()"
result = js_ast.Expr{Loc: loc, Data: &js_ast.EIf{
Test: js_ast.Expr{Loc: loc, Data: &js_ast.EBinary{
Op: js_ast.BinOpLooseEq,
Left: expr,
Right: js_ast.Expr{Loc: loc, Data: js_ast.ENullShared},
}},
Yes: valueWhenUndefined,
No: result,
}}
if exprWrapFunc != nil {
result = exprWrapFunc(result)
}
if targetWrapFunc != nil {
result = targetWrapFunc(result)
}
if childOut.thisArgWrapFunc != nil {
result = childOut.thisArgWrapFunc(result)
}
return result, exprOut{
thisArgFunc: parentThisArgFunc,
thisArgWrapFunc: parentThisArgWrapFunc,
}
}
func (p *parser) lowerParenthesizedOptionalChain(loc logger.Loc, e *js_ast.ECall, childOut exprOut) js_ast.Expr {
return childOut.thisArgWrapFunc(js_ast.Expr{Loc: loc, Data: &js_ast.ECall{
Target: js_ast.Expr{Loc: loc, Data: &js_ast.EDot{
Target: e.Target,
Name: "call",
NameLoc: loc,
}},
Args: append(append(make([]js_ast.Expr, 0, len(e.Args)+1), childOut.thisArgFunc()), e.Args...),
}})
}
func (p *parser) lowerAssignmentOperator(value js_ast.Expr, callback func(js_ast.Expr, js_ast.Expr) js_ast.Expr) js_ast.Expr {
switch left := value.Data.(type) {
case *js_ast.EDot:
if left.OptionalChain == js_ast.OptionalChainNone {
referenceFunc, wrapFunc := p.captureValueWithPossibleSideEffects(value.Loc, 2, left.Target, valueDefinitelyNotMutated)
return wrapFunc(callback(
js_ast.Expr{Loc: value.Loc, Data: &js_ast.EDot{
Target: referenceFunc(),
Name: left.Name,
NameLoc: left.NameLoc,
}},
js_ast.Expr{Loc: value.Loc, Data: &js_ast.EDot{
Target: referenceFunc(),
Name: left.Name,
NameLoc: left.NameLoc,
}},
))
}
case *js_ast.EIndex:
if left.OptionalChain == js_ast.OptionalChainNone {
targetFunc, targetWrapFunc := p.captureValueWithPossibleSideEffects(value.Loc, 2, left.Target, valueDefinitelyNotMutated)
indexFunc, indexWrapFunc := p.captureValueWithPossibleSideEffects(value.Loc, 2, left.Index, valueDefinitelyNotMutated)
return targetWrapFunc(indexWrapFunc(callback(
js_ast.Expr{Loc: value.Loc, Data: &js_ast.EIndex{
Target: targetFunc(),
Index: indexFunc(),
}},
js_ast.Expr{Loc: value.Loc, Data: &js_ast.EIndex{
Target: targetFunc(),
Index: indexFunc(),
}},
)))
}
case *js_ast.EIdentifier:
return callback(
js_ast.Expr{Loc: value.Loc, Data: &js_ast.EIdentifier{Ref: left.Ref}},
value,
)
}
// We shouldn't get here with valid syntax? Just let this through for now
// since there's currently no assignment target validation. Garbage in,
// garbage out.
return value
}
func (p *parser) lowerExponentiationAssignmentOperator(loc logger.Loc, e *js_ast.EBinary) js_ast.Expr {
if target, privateLoc, private := p.extractPrivateIndex(e.Left); private != nil {
// "a.#b **= c" => "__privateSet(a, #b, __pow(__privateGet(a, #b), c))"
targetFunc, targetWrapFunc := p.captureValueWithPossibleSideEffects(loc, 2, target, valueDefinitelyNotMutated)
return targetWrapFunc(p.lowerPrivateSet(targetFunc(), privateLoc, private,
p.callRuntime(loc, "__pow", []js_ast.Expr{
p.lowerPrivateGet(targetFunc(), privateLoc, private),
e.Right,
})))
}
return p.lowerAssignmentOperator(e.Left, func(a js_ast.Expr, b js_ast.Expr) js_ast.Expr {
// "a **= b" => "a = __pow(a, b)"
return js_ast.Assign(a, p.callRuntime(loc, "__pow", []js_ast.Expr{b, e.Right}))
})
}
func (p *parser) lowerNullishCoalescingAssignmentOperator(loc logger.Loc, e *js_ast.EBinary) js_ast.Expr {
if target, privateLoc, private := p.extractPrivateIndex(e.Left); private != nil {
if p.options.unsupportedJSFeatures.Has(compat.NullishCoalescing) {
// "a.#b ??= c" => "(_a = __privateGet(a, #b)) != null ? _a : __privateSet(a, #b, c)"
targetFunc, targetWrapFunc := p.captureValueWithPossibleSideEffects(loc, 2, target, valueDefinitelyNotMutated)
left := p.lowerPrivateGet(targetFunc(), privateLoc, private)
right := p.lowerPrivateSet(targetFunc(), privateLoc, private, e.Right)
return targetWrapFunc(p.lowerNullishCoalescing(loc, left, right))
}
// "a.#b ??= c" => "__privateGet(a, #b) ?? __privateSet(a, #b, c)"
targetFunc, targetWrapFunc := p.captureValueWithPossibleSideEffects(loc, 2, target, valueDefinitelyNotMutated)
return targetWrapFunc(js_ast.Expr{Loc: loc, Data: &js_ast.EBinary{
Op: js_ast.BinOpNullishCoalescing,
Left: p.lowerPrivateGet(targetFunc(), privateLoc, private),
Right: p.lowerPrivateSet(targetFunc(), privateLoc, private, e.Right),
}})
}
return p.lowerAssignmentOperator(e.Left, func(a js_ast.Expr, b js_ast.Expr) js_ast.Expr {
if p.options.unsupportedJSFeatures.Has(compat.NullishCoalescing) {
// "a ??= b" => "(_a = a) != null ? _a : a = b"
return p.lowerNullishCoalescing(loc, a, js_ast.Assign(b, e.Right))
}
// "a ??= b" => "a ?? (a = b)"
return js_ast.Expr{Loc: loc, Data: &js_ast.EBinary{
Op: js_ast.BinOpNullishCoalescing,
Left: a,
Right: js_ast.Assign(b, e.Right),
}}
})
}
func (p *parser) lowerLogicalAssignmentOperator(loc logger.Loc, e *js_ast.EBinary, op js_ast.OpCode) js_ast.Expr {
if target, privateLoc, private := p.extractPrivateIndex(e.Left); private != nil {
// "a.#b &&= c" => "__privateGet(a, #b) && __privateSet(a, #b, c)"
// "a.#b ||= c" => "__privateGet(a, #b) || __privateSet(a, #b, c)"
targetFunc, targetWrapFunc := p.captureValueWithPossibleSideEffects(loc, 2, target, valueDefinitelyNotMutated)
return targetWrapFunc(js_ast.Expr{Loc: loc, Data: &js_ast.EBinary{
Op: op,
Left: p.lowerPrivateGet(targetFunc(), privateLoc, private),
Right: p.lowerPrivateSet(targetFunc(), privateLoc, private, e.Right),
}})
}
return p.lowerAssignmentOperator(e.Left, func(a js_ast.Expr, b js_ast.Expr) js_ast.Expr {
// "a &&= b" => "a && (a = b)"
// "a ||= b" => "a || (a = b)"
return js_ast.Expr{Loc: loc, Data: &js_ast.EBinary{
Op: op,
Left: a,
Right: js_ast.Assign(b, e.Right),
}}
})
}
func (p *parser) lowerNullishCoalescing(loc logger.Loc, left js_ast.Expr, right js_ast.Expr) js_ast.Expr {
// "x ?? y" => "x != null ? x : y"
// "x() ?? y()" => "_a = x(), _a != null ? _a : y"
leftFunc, wrapFunc := p.captureValueWithPossibleSideEffects(loc, 2, left, valueDefinitelyNotMutated)
return wrapFunc(js_ast.Expr{Loc: loc, Data: &js_ast.EIf{
Test: js_ast.Expr{Loc: loc, Data: &js_ast.EBinary{
Op: js_ast.BinOpLooseNe,
Left: leftFunc(),
Right: js_ast.Expr{Loc: loc, Data: js_ast.ENullShared},
}},
Yes: leftFunc(),
No: right,
}})
}
// Lower object spread for environments that don't support them. Non-spread
// properties are grouped into object literals and then passed to the
// "__spreadValues" and "__spreadProps" functions like this:
//
// "{a, b, ...c, d, e}" => "__spreadProps(__spreadValues(__spreadProps({a, b}, c), {d, e})"
//
// If the object literal starts with a spread, then we pass an empty object
// literal to "__spreadValues" to make sure we clone the object:
//
// "{...a, b}" => "__spreadProps(__spreadValues({}, a), {b})"
//
// It's not immediately obvious why we don't compile everything to a single
// call to a function that takes any number of arguments, since that would be
// shorter. The reason is to preserve the order of side effects. Consider
// this code:
//
// let a = {
// get x() {
// b = {y: 2}
// return 1
// }
// }
// let b = {}
// let c = {...a, ...b}
//
// Converting the above code to "let c = __spreadFn({}, a, null, b)" means "c"
// becomes "{x: 1}" which is incorrect. Converting the above code instead to
// "let c = __spreadProps(__spreadProps({}, a), b)" means "c" becomes
// "{x: 1, y: 2}" which is correct.
func (p *parser) lowerObjectSpread(loc logger.Loc, e *js_ast.EObject) js_ast.Expr {
needsLowering := false
if p.options.unsupportedJSFeatures.Has(compat.ObjectRestSpread) {
for _, property := range e.Properties {
if property.Kind == js_ast.PropertySpread {
needsLowering = true
break
}
}
}
if !needsLowering {
return js_ast.Expr{Loc: loc, Data: e}
}
var result js_ast.Expr
properties := []js_ast.Property{}
for _, property := range e.Properties {
if property.Kind != js_ast.PropertySpread {
properties = append(properties, property)
continue
}
if len(properties) > 0 || result.Data == nil {
if result.Data == nil {
// "{a, ...b}" => "__spreadValues({a}, b)"
result = js_ast.Expr{Loc: loc, Data: &js_ast.EObject{
Properties: properties,
IsSingleLine: e.IsSingleLine,
}}
} else {
// "{...a, b, ...c}" => "__spreadValues(__spreadProps(__spreadValues({}, a), {b}), c)"
result = p.callRuntime(loc, "__spreadProps",
[]js_ast.Expr{result, {Loc: loc, Data: &js_ast.EObject{
Properties: properties,
IsSingleLine: e.IsSingleLine,
}}})
}
properties = []js_ast.Property{}
}
// "{a, ...b}" => "__spreadValues({a}, b)"
result = p.callRuntime(loc, "__spreadValues", []js_ast.Expr{result, property.ValueOrNil})
}
if len(properties) > 0 {
// "{...a, b}" => "__spreadProps(__spreadValues({}, a), {b})"
result = p.callRuntime(loc, "__spreadProps", []js_ast.Expr{result, {Loc: loc, Data: &js_ast.EObject{
Properties: properties,
IsSingleLine: e.IsSingleLine,
}}})
}
return result
}