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Source file src/cmd/vet/buildtag.go

Documentation: cmd/vet

  // Copyright 2013 The Go Authors. All rights reserved.
  // Use of this source code is governed by a BSD-style
  // license that can be found in the LICENSE file.
  
  package main
  
  import (
  	"bytes"
  	"fmt"
  	"os"
  	"strings"
  	"unicode"
  )
  
  var (
  	nl         = []byte("\n")
  	slashSlash = []byte("//")
  	plusBuild  = []byte("+build")
  )
  
  func badfLine(f *File, line int, format string, args ...interface{}) {
  	msg := fmt.Sprintf(format, args...)
  	fmt.Fprintf(os.Stderr, "%s:%d: %s\n", f.name, line, msg)
  	setExit(1)
  }
  
  // checkBuildTag checks that build tags are in the correct location and well-formed.
  func checkBuildTag(f *File) {
  	if !vet("buildtags") {
  		return
  	}
  
  	// we must look at the raw lines, as build tags may appear in non-Go
  	// files such as assembly files.
  	lines := bytes.SplitAfter(f.content, nl)
  
  	// lineWithComment reports whether a line corresponds to a comment in
  	// the source file. If the source file wasn't Go, the function always
  	// returns true.
  	lineWithComment := func(line int) bool {
  		if f.file == nil {
  			// Current source file is not Go, so be conservative.
  			return true
  		}
  		for _, group := range f.file.Comments {
  			startLine := f.fset.Position(group.Pos()).Line
  			endLine := f.fset.Position(group.End()).Line
  			if startLine <= line && line <= endLine {
  				return true
  			}
  		}
  		return false
  	}
  
  	// Determine cutpoint where +build comments are no longer valid.
  	// They are valid in leading // comments in the file followed by
  	// a blank line.
  	var cutoff int
  	for i, line := range lines {
  		line = bytes.TrimSpace(line)
  		if len(line) == 0 {
  			cutoff = i
  			continue
  		}
  		if bytes.HasPrefix(line, slashSlash) {
  			continue
  		}
  		break
  	}
  
  	for i, line := range lines {
  		line = bytes.TrimSpace(line)
  		if !bytes.HasPrefix(line, slashSlash) {
  			continue
  		}
  		if !bytes.Contains(line, plusBuild) {
  			// Check that the comment contains "+build" early, to
  			// avoid unnecessary lineWithComment calls that may
  			// incur linear searches.
  			continue
  		}
  		if !lineWithComment(i + 1) {
  			// This is a line in a Go source file that looks like a
  			// comment, but actually isn't - such as part of a raw
  			// string.
  			continue
  		}
  
  		text := bytes.TrimSpace(line[2:])
  		if bytes.HasPrefix(text, plusBuild) {
  			fields := bytes.Fields(text)
  			if !bytes.Equal(fields[0], plusBuild) {
  				// Comment is something like +buildasdf not +build.
  				badfLine(f, i+1, "possible malformed +build comment")
  				continue
  			}
  			if i >= cutoff {
  				badfLine(f, i+1, "+build comment must appear before package clause and be followed by a blank line")
  				continue
  			}
  			// Check arguments.
  		Args:
  			for _, arg := range fields[1:] {
  				for _, elem := range strings.Split(string(arg), ",") {
  					if strings.HasPrefix(elem, "!!") {
  						badfLine(f, i+1, "invalid double negative in build constraint: %s", arg)
  						break Args
  					}
  					elem = strings.TrimPrefix(elem, "!")
  					for _, c := range elem {
  						if !unicode.IsLetter(c) && !unicode.IsDigit(c) && c != '_' && c != '.' {
  							badfLine(f, i+1, "invalid non-alphanumeric build constraint: %s", arg)
  							break Args
  						}
  					}
  				}
  			}
  			continue
  		}
  		// Comment with +build but not at beginning.
  		if i < cutoff {
  			badfLine(f, i+1, "possible malformed +build comment")
  			continue
  		}
  	}
  }
  

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