4 files changed, 82 insertions, 4 deletions
diff --git a/src/cmd/compile/internal/noder/linker.go b/src/cmd/compile/internal/noder/linker.go
index 0f39fdec05..44de017ae5 100644
--- a/src/cmd/compile/internal/noder/linker.go
+++ b/src/cmd/compile/internal/noder/linker.go
@@ -5,6 +5,7 @@
 package noder
 
 import (
+	"internal/buildcfg"
 	"internal/pkgbits"
 	"io"
 
@@ -269,6 +270,16 @@ func (l *linker) relocFuncExt(w *pkgbits.Encoder, name *ir.Name) {
 	l.pragmaFlag(w, name.Func.Pragma)
 	l.linkname(w, name)
 
+	if buildcfg.GOARCH == "wasm" {
+		if name.Func.WasmImport != nil {
+			w.String(name.Func.WasmImport.Module)
+			w.String(name.Func.WasmImport.Name)
+		} else {
+			w.String("")
+			w.String("")
+		}
+	}
+
 	// Relocated extension data.
 	w.Bool(true)
 
diff --git a/src/cmd/compile/internal/noder/noder.go b/src/cmd/compile/internal/noder/noder.go
index 10619bf569..16113e37a3 100644
--- a/src/cmd/compile/internal/noder/noder.go
+++ b/src/cmd/compile/internal/noder/noder.go
@@ -7,6 +7,7 @@ package noder
 import (
 	"errors"
 	"fmt"
+	"internal/buildcfg"
 	"os"
 	"path/filepath"
 	"runtime"
@@ -166,9 +167,17 @@ var allowedStdPragmas = map[string]bool{
 
 // *pragmas is the value stored in a syntax.pragmas during parsing.
 type pragmas struct {
-	Flag   ir.PragmaFlag // collected bits
-	Pos    []pragmaPos   // position of each individual flag
-	Embeds []pragmaEmbed
+	Flag       ir.PragmaFlag // collected bits
+	Pos        []pragmaPos   // position of each individual flag
+	Embeds     []pragmaEmbed
+	WasmImport *WasmImport
+}
+
+// WasmImport stores metadata associated with the //go:wasmimport pragma
+type WasmImport struct {
+	Pos    syntax.Pos
+	Module string
+	Name   string
 }
 
 type pragmaPos struct {
@@ -192,6 +201,9 @@ func (p *noder) checkUnusedDuringParse(pragma *pragmas) {
 			p.error(syntax.Error{Pos: e.Pos, Msg: "misplaced go:embed directive"})
 		}
 	}
+	if pragma.WasmImport != nil {
+		p.error(syntax.Error{Pos: pragma.WasmImport.Pos, Msg: "misplaced go:wasmimport directive"})
+	}
 }
 
 // pragma is called concurrently if files are parsed concurrently.
@@ -219,6 +231,25 @@ func (p *noder) pragma(pos syntax.Pos, blankLine bool, text string, old syntax.P
 	}
 
 	switch {
+	case strings.HasPrefix(text, "go:wasmimport "):
+		f := strings.Fields(text)
+		if len(f) != 3 {
+			p.error(syntax.Error{Pos: pos, Msg: "usage: //go:wasmimport importmodule importname"})
+			break
+		}
+		if !base.Flag.CompilingRuntime && base.Ctxt.Pkgpath != "syscall/js" && base.Ctxt.Pkgpath != "syscall/js_test" {
+			p.error(syntax.Error{Pos: pos, Msg: "//go:wasmimport directive cannot be used outside of runtime or syscall/js"})
+			break
+		}
+
+		if buildcfg.GOARCH == "wasm" {
+			// Only actually use them if we're compiling to WASM though.
+			pragma.WasmImport = &WasmImport{
+				Pos:    pos,
+				Module: f[1],
+				Name:   f[2],
+			}
+		}
 	case strings.HasPrefix(text, "go:linkname "):
 		f := strings.Fields(text)
 		if !(2 <= len(f) && len(f) <= 3) {
diff --git a/src/cmd/compile/internal/noder/reader.go b/src/cmd/compile/internal/noder/reader.go
index b7605e9317..e4ab80b2d0 100644
--- a/src/cmd/compile/internal/noder/reader.go
+++ b/src/cmd/compile/internal/noder/reader.go
@@ -1081,6 +1081,18 @@ func (r *reader) funcExt(name *ir.Name, method *types.Sym) {
 	fn.Pragma = r.pragmaFlag()
 	r.linkname(name)
 
+	if buildcfg.GOARCH == "wasm" {
+		xmod := r.String()
+		xname := r.String()
+
+		if xmod != "" && xname != "" {
+			fn.WasmImport = &ir.WasmImport{
+				Module: xmod,
+				Name:   xname,
+			}
+		}
+	}
+
 	typecheck.Func(fn)
 
 	if r.Bool() {
diff --git a/src/cmd/compile/internal/noder/writer.go b/src/cmd/compile/internal/noder/writer.go
index da5c1e910d..5dd8d1de2d 100644
--- a/src/cmd/compile/internal/noder/writer.go
+++ b/src/cmd/compile/internal/noder/writer.go
@@ -6,6 +6,7 @@ package noder
 
 import (
 	"fmt"
+	"internal/buildcfg"
 	"internal/pkgbits"
 
 	"cmd/compile/internal/base"
@@ -1003,11 +1004,15 @@ func (w *writer) funcExt(obj *types2.Func) {
 	if pragma&ir.Systemstack != 0 && pragma&ir.Nosplit != 0 {
 		w.p.errorf(decl, "go:nosplit and go:systemstack cannot be combined")
 	}
+	wi := asWasmImport(decl.Pragma)
 
 	if decl.Body != nil {
 		if pragma&ir.Noescape != 0 {
 			w.p.errorf(decl, "can only use //go:noescape with external func implementations")
 		}
+		if wi != nil {
+			w.p.errorf(decl, "can only use //go:wasmimport with external func implementations")
+		}
 		if (pragma&ir.UintptrKeepAlive != 0 && pragma&ir.UintptrEscapes == 0) && pragma&ir.Nosplit == 0 {
 			// Stack growth can't handle uintptr arguments that may
 			// be pointers (as we don't know which are pointers
@@ -1028,7 +1033,8 @@ func (w *writer) funcExt(obj *types2.Func) {
 		if base.Flag.Complete || decl.Name.Value == "init" {
 			// Linknamed functions are allowed to have no body. Hopefully
 			// the linkname target has a body. See issue 23311.
-			if _, ok := w.p.linknames[obj]; !ok {
+			// Wasmimport functions are also allowed to have no body.
+			if _, ok := w.p.linknames[obj]; !ok && wi == nil {
 				w.p.errorf(decl, "missing function body")
 			}
 		}
@@ -1041,6 +1047,17 @@ func (w *writer) funcExt(obj *types2.Func) {
 	w.Sync(pkgbits.SyncFuncExt)
 	w.pragmaFlag(pragma)
 	w.linkname(obj)
+
+	if buildcfg.GOARCH == "wasm" {
+		if wi != nil {
+			w.String(wi.Module)
+			w.String(wi.Name)
+		} else {
+			w.String("")
+			w.String("")
+		}
+	}
+
 	w.Bool(false) // stub extension
 	w.Reloc(pkgbits.RelocBody, body)
 	w.Sync(pkgbits.SyncEOF)
@@ -2728,6 +2745,13 @@ func asPragmaFlag(p syntax.Pragma) ir.PragmaFlag {
 	return p.(*pragmas).Flag
 }
 
+func asWasmImport(p syntax.Pragma) *WasmImport {
+	if p == nil {
+		return nil
+	}
+	return p.(*pragmas).WasmImport
+}
+
 // isPtrTo reports whether from is the type *to.
 func isPtrTo(from, to types2.Type) bool {
 	ptr, ok := from.(*types2.Pointer)