1 files changed, 248 insertions, 20 deletions

diff --git a/src/go/build/read.go b/src/go/build/read.go
index 29b8cdc786..6806a51c24 100644
--- a/src/go/build/read.go
+++ b/src/go/build/read.go
@@ -7,7 +7,13 @@ package build
 import (
 	"bufio"
 	"errors"
+	"fmt"
+	"go/ast"
+	"go/parser"
 	"io"
+	"strconv"
+	"strings"
+	"unicode"
 	"unicode/utf8"
 )
 
@@ -57,6 +63,29 @@ func (r *importReader) readByte() byte {
 	return c
 }
 
+// readByteNoBuf is like readByte but doesn't buffer the byte.
+// It exhausts r.buf before reading from r.b.
+func (r *importReader) readByteNoBuf() byte {
+	if len(r.buf) > 0 {
+		c := r.buf[0]
+		r.buf = r.buf[1:]
+		return c
+	}
+	c, err := r.b.ReadByte()
+	if err == nil && c == 0 {
+		err = errNUL
+	}
+	if err != nil {
+		if err == io.EOF {
+			r.eof = true
+		} else if r.err == nil {
+			r.err = err
+		}
+		c = 0
+	}
+	return c
+}
+
 // peekByte returns the next byte from the input reader but does not advance beyond it.
 // If skipSpace is set, peekByte skips leading spaces and comments.
 func (r *importReader) peekByte(skipSpace bool) byte {
@@ -117,6 +146,74 @@ func (r *importReader) nextByte(skipSpace bool) byte {
 	return c
 }
 
+var goEmbed = []byte("go:embed")
+
+// findEmbed advances the input reader to the next //go:embed comment.
+// It reports whether it found a comment.
+// (Otherwise it found an error or EOF.)
+func (r *importReader) findEmbed(first bool) bool {
+	// The import block scan stopped after a non-space character,
+	// so the reader is not at the start of a line on the first call.
+	// After that, each //go:embed extraction leaves the reader
+	// at the end of a line.
+	startLine := !first
+	var c byte
+	for r.err == nil && !r.eof {
+		c = r.readByteNoBuf()
+	Reswitch:
+		switch c {
+		default:
+			startLine = false
+
+		case '\n':
+			startLine = true
+
+		case ' ', '\t':
+			// leave startLine alone
+
+		case '/':
+			c = r.readByteNoBuf()
+			switch c {
+			default:
+				startLine = false
+				goto Reswitch
+
+			case '*':
+				var c1 byte
+				for (c != '*' || c1 != '/') && r.err == nil {
+					if r.eof {
+						r.syntaxError()
+					}
+					c, c1 = c1, r.readByteNoBuf()
+				}
+				startLine = false
+
+			case '/':
+				if startLine {
+					// Try to read this as a //go:embed comment.
+					for i := range goEmbed {
+						c = r.readByteNoBuf()
+						if c != goEmbed[i] {
+							goto SkipSlashSlash
+						}
+					}
+					c = r.readByteNoBuf()
+					if c == ' ' || c == '\t' {
+						// Found one!
+						return true
+					}
+				}
+			SkipSlashSlash:
+				for c != '\n' && r.err == nil && !r.eof {
+					c = r.readByteNoBuf()
+				}
+				startLine = true
+			}
+		}
+	}
+	return false
+}
+
 // readKeyword reads the given keyword from the input.
 // If the keyword is not present, readKeyword records a syntax error.
 func (r *importReader) readKeyword(kw string) {
@@ -147,15 +244,11 @@ func (r *importReader) readIdent() {
 
 // readString reads a quoted string literal from the input.
 // If an identifier is not present, readString records a syntax error.
-func (r *importReader) readString(save *[]string) {
+func (r *importReader) readString() {
 	switch r.nextByte(true) {
 	case '`':
-		start := len(r.buf) - 1
 		for r.err == nil {
 			if r.nextByte(false) == '`' {
-				if save != nil {
-					*save = append(*save, string(r.buf[start:]))
-				}
 				break
 			}
 			if r.eof {
@@ -163,13 +256,9 @@ func (r *importReader) readString(save *[]string) {
 			}
 		}
 	case '"':
-		start := len(r.buf) - 1
 		for r.err == nil {
 			c := r.nextByte(false)
 			if c == '"' {
-				if save != nil {
-					*save = append(*save, string(r.buf[start:]))
-				}
 				break
 			}
 			if r.eof || c == '\n' {
@@ -186,17 +275,17 @@ func (r *importReader) readString(save *[]string) {
 
 // readImport reads an import clause - optional identifier followed by quoted string -
 // from the input.
-func (r *importReader) readImport(imports *[]string) {
+func (r *importReader) readImport() {
 	c := r.peekByte(true)
 	if c == '.' {
 		r.peek = 0
 	} else if isIdent(c) {
 		r.readIdent()
 	}
-	r.readString(imports)
+	r.readString()
 }
 
-// readComments is like ioutil.ReadAll, except that it only reads the leading
+// readComments is like io.ReadAll, except that it only reads the leading
 // block of comments in the file.
 func readComments(f io.Reader) ([]byte, error) {
 	r := &importReader{b: bufio.NewReader(f)}
@@ -208,9 +297,14 @@ func readComments(f io.Reader) ([]byte, error) {
 	return r.buf, r.err
 }
 
-// readImports is like ioutil.ReadAll, except that it expects a Go file as input
-// and stops reading the input once the imports have completed.
-func readImports(f io.Reader, reportSyntaxError bool, imports *[]string) ([]byte, error) {
+// readGoInfo expects a Go file as input and reads the file up to and including the import section.
+// It records what it learned in *info.
+// If info.fset is non-nil, readGoInfo parses the file and sets info.parsed, info.parseErr,
+// info.imports, info.embeds, and info.embedErr.
+//
+// It only returns an error if there are problems reading the file,
+// not for syntax errors in the file itself.
+func readGoInfo(f io.Reader, info *fileInfo) error {
 	r := &importReader{b: bufio.NewReader(f)}
 
 	r.readKeyword("package")
@@ -220,28 +314,162 @@ func readImports(f io.Reader, reportSyntaxError bool, imports *[]string) ([]byte
 		if r.peekByte(true) == '(' {
 			r.nextByte(false)
 			for r.peekByte(true) != ')' && r.err == nil {
-				r.readImport(imports)
+				r.readImport()
 			}
 			r.nextByte(false)
 		} else {
-			r.readImport(imports)
+			r.readImport()
 		}
 	}
 
+	info.header = r.buf
+
 	// If we stopped successfully before EOF, we read a byte that told us we were done.
 	// Return all but that last byte, which would cause a syntax error if we let it through.
 	if r.err == nil && !r.eof {
-		return r.buf[:len(r.buf)-1], nil
+		info.header = r.buf[:len(r.buf)-1]
 	}
 
 	// If we stopped for a syntax error, consume the whole file so that
 	// we are sure we don't change the errors that go/parser returns.
-	if r.err == errSyntax && !reportSyntaxError {
+	if r.err == errSyntax {
 		r.err = nil
 		for r.err == nil && !r.eof {
 			r.readByte()
 		}
+		info.header = r.buf
+	}
+	if r.err != nil {
+		return r.err
+	}
+
+	if info.fset == nil {
+		return nil
+	}
+
+	// Parse file header & record imports.
+	info.parsed, info.parseErr = parser.ParseFile(info.fset, info.name, info.header, parser.ImportsOnly|parser.ParseComments)
+	if info.parseErr != nil {
+		return nil
+	}
+
+	hasEmbed := false
+	for _, decl := range info.parsed.Decls {
+		d, ok := decl.(*ast.GenDecl)
+		if !ok {
+			continue
+		}
+		for _, dspec := range d.Specs {
+			spec, ok := dspec.(*ast.ImportSpec)
+			if !ok {
+				continue
+			}
+			quoted := spec.Path.Value
+			path, err := strconv.Unquote(quoted)
+			if err != nil {
+				return fmt.Errorf("parser returned invalid quoted string: <%s>", quoted)
+			}
+			if path == "embed" {
+				hasEmbed = true
+			}
+
+			doc := spec.Doc
+			if doc == nil && len(d.Specs) == 1 {
+				doc = d.Doc
+			}
+			info.imports = append(info.imports, fileImport{path, spec.Pos(), doc})
+		}
 	}
 
-	return r.buf, r.err
+	// If the file imports "embed",
+	// we have to look for //go:embed comments
+	// in the remainder of the file.
+	// The compiler will enforce the mapping of comments to
+	// declared variables. We just need to know the patterns.
+	// If there were //go:embed comments earlier in the file
+	// (near the package statement or imports), the compiler
+	// will reject them. They can be (and have already been) ignored.
+	if hasEmbed {
+		var line []byte
+		for first := true; r.findEmbed(first); first = false {
+			line = line[:0]
+			for {
+				c := r.readByteNoBuf()
+				if c == '\n' || r.err != nil || r.eof {
+					break
+				}
+				line = append(line, c)
+			}
+			// Add args if line is well-formed.
+			// Ignore badly-formed lines - the compiler will report them when it finds them,
+			// and we can pretend they are not there to help go list succeed with what it knows.
+			args, err := parseGoEmbed(string(line))
+			if err == nil {
+				info.embeds = append(info.embeds, args...)
+			}
+		}
+	}
+
+	return nil
+}
+
+// parseGoEmbed parses the text following "//go:embed" to extract the glob patterns.
+// It accepts unquoted space-separated patterns as well as double-quoted and back-quoted Go strings.
+// There is a copy of this code in cmd/compile/internal/gc/noder.go as well.
+func parseGoEmbed(args string) ([]string, error) {
+	var list []string
+	for args = strings.TrimSpace(args); args != ""; args = strings.TrimSpace(args) {
+		var path string
+	Switch:
+		switch args[0] {
+		default:
+			i := len(args)
+			for j, c := range args {
+				if unicode.IsSpace(c) {
+					i = j
+					break
+				}
+			}
+			path = args[:i]
+			args = args[i:]
+
+		case '`':
+			i := strings.Index(args[1:], "`")
+			if i < 0 {
+				return nil, fmt.Errorf("invalid quoted string in //go:embed: %s", args)
+			}
+			path = args[1 : 1+i]
+			args = args[1+i+1:]
+
+		case '"':
+			i := 1
+			for ; i < len(args); i++ {
+				if args[i] == '\\' {
+					i++
+					continue
+				}
+				if args[i] == '"' {
+					q, err := strconv.Unquote(args[:i+1])
+					if err != nil {
+						return nil, fmt.Errorf("invalid quoted string in //go:embed: %s", args[:i+1])
+					}
+					path = q
+					args = args[i+1:]
+					break Switch
+				}
+			}
+			if i >= len(args) {
+				return nil, fmt.Errorf("invalid quoted string in //go:embed: %s", args)
+			}
+		}
+
+		if args != "" {
+			r, _ := utf8.DecodeRuneInString(args)
+			if !unicode.IsSpace(r) {
+				return nil, fmt.Errorf("invalid quoted string in //go:embed: %s", args)
+			}
+		}
+		list = append(list, path)
+	}
+	return list, nil
 }