Revert "Revert "cmd/go/internal/modload: record the replacement for the module containing package main in BuildInfo""

This reverts CL 220722.

Reason for revert: rolling forward with fix.

Fixes #37392

Change-Id: Iba8b0c645267777fbb7019976292d691a10b906a
Reviewed-on: https://go-review.googlesource.com/c/go/+/220898
Run-TryBot: Bryan C. Mills <bcmills@google.com>
Reviewed-by: Jay Conrod <jayconrod@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

5 files changed, 90 insertions, 36 deletions

diff --git a/src/cmd/go/internal/modload/build.go b/src/cmd/go/internal/modload/build.go
index 6fa47d7400..454dbf28cf 100644
--- a/src/cmd/go/internal/modload/build.go
+++ b/src/cmd/go/internal/modload/build.go
@@ -207,6 +207,7 @@ func PackageBuildInfo(path string, deps []string) string {
 	if isStandardImportPath(path) || !Enabled() {
 		return ""
 	}
+
 	target := mustFindModule(path, path)
 	mdeps := make(map[module.Version]bool)
 	for _, dep := range deps {
@@ -223,26 +224,25 @@ func PackageBuildInfo(path string, deps []string) string {
 
 	var buf bytes.Buffer
 	fmt.Fprintf(&buf, "path\t%s\n", path)
-	tv := target.Version
-	if tv == "" {
-		tv = "(devel)"
-	}
-	fmt.Fprintf(&buf, "mod\t%s\t%s\t%s\n", target.Path, tv, modfetch.Sum(target))
-	for _, mod := range mods {
-		mv := mod.Version
+
+	writeEntry := func(token string, m module.Version) {
+		mv := m.Version
 		if mv == "" {
 			mv = "(devel)"
 		}
-		r := Replacement(mod)
-		h := ""
-		if r.Path == "" {
-			h = "\t" + modfetch.Sum(mod)
-		}
-		fmt.Fprintf(&buf, "dep\t%s\t%s%s\n", mod.Path, mv, h)
-		if r.Path != "" {
-			fmt.Fprintf(&buf, "=>\t%s\t%s\t%s\n", r.Path, r.Version, modfetch.Sum(r))
+		fmt.Fprintf(&buf, "%s\t%s\t%s", token, m.Path, mv)
+		if r := Replacement(m); r.Path == "" {
+			fmt.Fprintf(&buf, "\t%s\n", modfetch.Sum(m))
+		} else {
+			fmt.Fprintf(&buf, "\n=>\t%s\t%s\t%s\n", r.Path, r.Version, modfetch.Sum(r))
 		}
 	}
+
+	writeEntry("mod", target)
+	for _, mod := range mods {
+		writeEntry("dep", mod)
+	}
+
 	return buf.String()
 }
 
diff --git a/src/cmd/go/testdata/mod/example.com_printversion_v0.1.0.txt b/src/cmd/go/testdata/mod/example.com_printversion_v0.1.0.txt
index bae8b13d47..606322ac86 100644
--- a/src/cmd/go/testdata/mod/example.com_printversion_v0.1.0.txt
+++ b/src/cmd/go/testdata/mod/example.com_printversion_v0.1.0.txt
@@ -21,7 +21,13 @@ func main() {
 	info, _ := debug.ReadBuildInfo()
 	fmt.Fprintf(os.Stdout, "path is %s\n", info.Path)
 	fmt.Fprintf(os.Stdout, "main is %s %s\n", info.Main.Path, info.Main.Version)
+	if r := info.Main.Replace; r != nil {
+		fmt.Fprintf(os.Stdout, "\t(replaced by %s %s)\n", r.Path, r.Version)
+	}
 	for _, m := range info.Deps {
 		fmt.Fprintf(os.Stdout, "using %s %s\n", m.Path, m.Version)
+		if r := m.Replace; r != nil {
+			fmt.Fprintf(os.Stdout, "\t(replaced by %s %s)\n", r.Path, r.Version)
+		}
 	}
 }
diff --git a/src/cmd/go/testdata/mod/example.com_printversion_v1.0.0.txt b/src/cmd/go/testdata/mod/example.com_printversion_v1.0.0.txt
index 246741821a..b9b71e9538 100644
--- a/src/cmd/go/testdata/mod/example.com_printversion_v1.0.0.txt
+++ b/src/cmd/go/testdata/mod/example.com_printversion_v1.0.0.txt
@@ -29,7 +29,13 @@ func main() {
 	info, _ := debug.ReadBuildInfo()
 	fmt.Fprintf(os.Stdout, "path is %s\n", info.Path)
 	fmt.Fprintf(os.Stdout, "main is %s %s\n", info.Main.Path, info.Main.Version)
+	if r := info.Main.Replace; r != nil {
+		fmt.Fprintf(os.Stdout, "\t(replaced by %s %s)\n", r.Path, r.Version)
+	}
 	for _, m := range info.Deps {
 		fmt.Fprintf(os.Stdout, "using %s %s\n", m.Path, m.Version)
+		if r := m.Replace; r != nil {
+			fmt.Fprintf(os.Stdout, "\t(replaced by %s %s)\n", r.Path, r.Version)
+		}
 	}
 }
diff --git a/src/cmd/go/testdata/script/version_replace.txt b/src/cmd/go/testdata/script/version_replace.txt
new file mode 100644
index 0000000000..b657086f09
--- /dev/null
+++ b/src/cmd/go/testdata/script/version_replace.txt
@@ -0,0 +1,33 @@
+[short] skip
+
+go mod download example.com/printversion@v0.1.0 example.com/printversion@v1.0.0
+
+go install example.com/printversion
+
+go run example.com/printversion
+cmp stdout out.txt
+
+go version -m $GOPATH/bin/printversion$GOEXE
+stdout '^.*[/\\]bin[/\\]printversion'$GOEXE': .*$'
+stdout '^	path	example.com/printversion$'
+stdout '^	mod	example.com/printversion	v0.1.0$'
+stdout '^	=>	example.com/printversion	v1.0.0	h1:.*$'
+stdout '^	dep	example.com/version	v1.0.0$'
+stdout '^	=>	example.com/version	v1.0.1	h1:.*$'
+
+-- go.mod --
+module golang.org/issue/37392
+go 1.14
+require (
+	example.com/printversion v0.1.0
+)
+replace (
+	example.com/printversion => example.com/printversion v1.0.0
+	example.com/version v1.0.0 => example.com/version v1.0.1
+)
+-- out.txt --
+path is example.com/printversion
+main is example.com/printversion v0.1.0
+	(replaced by example.com/printversion v1.0.0)
+using example.com/version v1.0.0
+	(replaced by example.com/version v1.0.1)
diff --git a/src/runtime/debug/mod.go b/src/runtime/debug/mod.go
index 837cd689a0..0381bdcc53 100644
--- a/src/runtime/debug/mod.go
+++ b/src/runtime/debug/mod.go
@@ -47,9 +47,27 @@ func readBuildInfo(data string) (*BuildInfo, bool) {
 		repLine  = "=>\t"
 	)
 
-	info := &BuildInfo{}
+	readEntryFirstLine := func(elem []string) (Module, bool) {
+		if len(elem) != 2 && len(elem) != 3 {
+			return Module{}, false
+		}
+		sum := ""
+		if len(elem) == 3 {
+			sum = elem[2]
+		}
+		return Module{
+			Path:    elem[0],
+			Version: elem[1],
+			Sum:     sum,
+		}, true
+	}
 
-	var line string
+	var (
+		info = &BuildInfo{}
+		last *Module
+		line string
+		ok   bool
+	)
 	// Reverse of cmd/go/internal/modload.PackageBuildInfo
 	for len(data) > 0 {
 		i := strings.IndexByte(data, '\n')
@@ -63,42 +81,33 @@ func readBuildInfo(data string) (*BuildInfo, bool) {
 			info.Path = elem
 		case strings.HasPrefix(line, modLine):
 			elem := strings.Split(line[len(modLine):], "\t")
-			if len(elem) != 3 {
+			last = &info.Main
+			*last, ok = readEntryFirstLine(elem)
+			if !ok {
 				return nil, false
 			}
-			info.Main = Module{
-				Path:    elem[0],
-				Version: elem[1],
-				Sum:     elem[2],
-			}
 		case strings.HasPrefix(line, depLine):
 			elem := strings.Split(line[len(depLine):], "\t")
-			if len(elem) != 2 && len(elem) != 3 {
+			last = new(Module)
+			info.Deps = append(info.Deps, last)
+			*last, ok = readEntryFirstLine(elem)
+			if !ok {
 				return nil, false
 			}
-			sum := ""
-			if len(elem) == 3 {
-				sum = elem[2]
-			}
-			info.Deps = append(info.Deps, &Module{
-				Path:    elem[0],
-				Version: elem[1],
-				Sum:     sum,
-			})
 		case strings.HasPrefix(line, repLine):
 			elem := strings.Split(line[len(repLine):], "\t")
 			if len(elem) != 3 {
 				return nil, false
 			}
-			last := len(info.Deps) - 1
-			if last < 0 {
+			if last == nil {
 				return nil, false
 			}
-			info.Deps[last].Replace = &Module{
+			last.Replace = &Module{
 				Path:    elem[0],
 				Version: elem[1],
 				Sum:     elem[2],
 			}
+			last = nil
 		}
 	}
 	return info, true