cmd/go: diagnose invalid coverage runs

# bufio
coverage analysis cannot handle package (bufio_test imports testing imports bufio)
# bytes
coverage analysis cannot handle package (bytes_test imports encoding/base64 imports bytes)
# crypto/cipher
coverage analysis cannot handle package (cipher_test imports crypto/aes imports crypto/cipher)
# debug/dwarf
coverage analysis cannot handle package (dwarf_test imports debug/elf imports debug/dwarf)
# errors
coverage analysis cannot handle package (errors_test imports fmt imports errors)
# flag
coverage analysis cannot handle package (flag_test imports testing imports flag)
# fmt
coverage analysis cannot handle package (fmt_test imports testing imports fmt)
# go/ast
coverage analysis cannot handle package (ast_test imports go/format imports go/ast)
# image
coverage analysis cannot handle package (image_test imports image/gif imports image)
# io
coverage analysis cannot handle package (io_test imports bytes imports io)
# math
coverage analysis cannot handle package (math_test imports fmt imports math)
# net/http
coverage analysis cannot handle package (http_test imports net/http/httptest imports net/http)
# os
coverage analysis cannot handle package (os_test imports flag imports os)
# path/filepath
coverage analysis cannot handle package (filepath_test imports io/ioutil imports path/filepath)
# reflect
coverage analysis cannot handle package (reflect_test imports flag imports reflect)
# runtime
coverage analysis cannot handle package (runtime_test imports fmt imports runtime)
# runtime/pprof
coverage analysis cannot handle package (pprof_test imports testing imports runtime/pprof)
# sort
coverage analysis cannot handle package (sort_test imports testing imports sort)
# strconv
coverage analysis cannot handle package (strconv_test imports fmt imports strconv)
# strings
coverage analysis cannot handle package (strings_test imports testing imports strings)
# sync
coverage analysis cannot handle package (sync_test imports fmt imports sync)
# sync/atomic
coverage analysis cannot handle package (atomic_test imports testing imports sync/atomic)
# syscall
coverage analysis cannot handle package (syscall_test imports flag imports syscall)
# text/tabwriter
coverage analysis cannot handle package (tabwriter_test imports testing imports text/tabwriter)
# time
coverage analysis cannot handle package (time_test imports encoding/gob imports time)
# unicode
coverage analysis cannot handle package (unicode_test imports testing imports unicode)
# unicode/utf8
coverage analysis cannot handle package (utf8_test imports bytes imports unicode/utf8)

R=r
CC=golang-dev
https://golang.org/cl/10216043

src/cmd/go/test.go

@@ -435,6 +435,15 @@ func runTest(cmd *Command, args []string) {
 	b.do(root)
 }
 
+func contains(x []string, s string) bool {
+	for _, t := range x {
+		if t == s {
+			return true
+		}
+	}
+	return false
+}
+
 func (b *builder) test(p *Package) (buildAction, runAction, printAction *action, err error) {
 	if len(p.TestGoFiles)+len(p.XTestGoFiles) == 0 {
 		build := &action{p: p}
@@ -468,6 +477,19 @@ func (b *builder) test(p *Package) (buildAction, runAction, printAction *action,
 			return nil, nil, nil, p1.Error
 		}
 		ximports = append(ximports, p1)
+
+		// In coverage mode, we rewrite the package p's sources.
+		// All code that imports p must be rebuilt with the updated
+		// copy, or else coverage will at the least be incomplete
+		// (and sometimes we get link errors due to the mismatch as well).
+		// The external test itself imports package p, of course, but
+		// we make sure that sees the new p. Any other code in the test
+		// - that is, any code imported by the external test that in turn
+		// imports p - needs to be rebuilt too. For now, just report
+		// that coverage is unavailable.
+		if testCover != "" && contains(p1.Deps, p.ImportPath) {
+			return nil, nil, nil, fmt.Errorf("coverage analysis cannot handle package (%s_test imports %s imports %s)", p.Name, path, p.ImportPath)
+		}
 	}
 	stk.pop()