func readGoInfo()

in go/tools/builders/read.go [369:478]
84 lines of code
28 McCabe index (conditional complexity)

func readGoInfo(f io.Reader, info *fileInfo) error {
	r := newImportReader(info.filename, f)

	r.readKeyword("package")
	r.readIdent()
	for r.peekByte(true) == 'i' {
		r.readKeyword("import")
		if r.peekByte(true) == '(' {
			r.nextByte(false)
			for r.peekByte(true) != ')' && r.err == nil {
				r.readImport()
			}
			r.nextByte(false)
		} else {
			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 {
		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 {
		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.filename, info.header, parser.ImportsOnly|parser.ParseComments)
	if info.parseErr != nil {
		return nil
	}
	info.pkg = info.parsed.Name.Name

	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})
		}
	}

	// 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]
			pos := r.pos
			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.
			embs, err := parseGoEmbed(string(line), pos)
			if err == nil {
				info.embeds = append(info.embeds, embs...)
			}
		}
	}

	return nil
}