cmd/go/internal/modload: annotate replacements in PackageNotInModuleError

Fixes #34085

Change-Id: I3111f5997466ad33f51e80c71f5fb2ccebdcc6e4
Reviewed-on: https://go-review.googlesource.com/c/go/+/193617
Run-TryBot: Bryan C. Mills <bcmills@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Jay Conrod <jayconrod@google.com>

src/cmd/go/internal/modload/import_test.go

@@ -21,7 +21,7 @@ var importTests = []struct {
 	},
 	{
 		path: "golang.org/x/net",
-		err:  "module golang.org/x/net@.* found, but does not contain package golang.org/x/net",
+		err:  `module golang.org/x/net@.* found \(v0.0.0-.*\), but does not contain package golang.org/x/net`,
 	},
 	{
 		path: "golang.org/x/text",

src/cmd/go/internal/modload/load.go

@@ -1205,6 +1205,11 @@ func (*mvsReqs) next(m module.Version) (module.Version, error) {
 	return module.Version{Path: m.Path, Version: "none"}, nil
 }
 
+// fetch downloads the given module (or its replacement)
+// and returns its location.
+//
+// The isLocal return value reports whether the replacement,
+// if any, is local to the filesystem.
 func fetch(mod module.Version) (dir string, isLocal bool, err error) {
 	if mod == Target {
 		return ModRoot(), true, nil

src/cmd/go/internal/modload/query.go

@@ -381,9 +381,10 @@ func QueryPattern(pattern, query string, allowed func(module.Version) bool) ([]Q
 			r.Packages = match(r.Mod, root, isLocal)
 			if len(r.Packages) == 0 {
 				return r, &PackageNotInModuleError{
-					Mod:     r.Mod,
-					Query:   query,
-					Pattern: pattern,
+					Mod:         r.Mod,
+					Replacement: Replacement(r.Mod),
+					Query:       query,
+					Pattern:     pattern,
 				}
 			}
 			return r, nil
@@ -536,21 +537,32 @@ func (e *NoMatchingVersionError) Error() string {
 // code for the versions it knows about, and thus did not have the opportunity
 // to return a non-400 status code to suppress fallback.
 type PackageNotInModuleError struct {
-	Mod     module.Version
-	Query   string
-	Pattern string
+	Mod         module.Version
+	Replacement module.Version
+	Query       string
+	Pattern     string
 }
 
 func (e *PackageNotInModuleError) Error() string {
 	found := ""
-	if e.Query != e.Mod.Version {
+	if r := e.Replacement; r.Path != "" {
+		replacement := r.Path
+		if r.Version != "" {
+			replacement = fmt.Sprintf("%s@%s", r.Path, r.Version)
+		}
+		if e.Query == e.Mod.Version {
+			found = fmt.Sprintf(" (replaced by %s)", replacement)
+		} else {
+			found = fmt.Sprintf(" (%s, replaced by %s)", e.Mod.Version, replacement)
+		}
+	} else if e.Query != e.Mod.Version {
 		found = fmt.Sprintf(" (%s)", e.Mod.Version)
 	}
 
 	if strings.Contains(e.Pattern, "...") {
-		return fmt.Sprintf("module %s@%s%s found, but does not contain packages matching %s", e.Mod.Path, e.Query, found, e.Pattern)
+		return fmt.Sprintf("module %s@%s found%s, but does not contain packages matching %s", e.Mod.Path, e.Query, found, e.Pattern)
 	}
-	return fmt.Sprintf("module %s@%s%s found, but does not contain package %s", e.Mod.Path, e.Query, found, e.Pattern)
+	return fmt.Sprintf("module %s@%s found%s, but does not contain package %s", e.Mod.Path, e.Query, found, e.Pattern)
 }
 
 // ModuleHasRootPackage returns whether module m contains a package m.Path.

src/cmd/go/testdata/script/mod_get_patterns.txt

@@ -10,11 +10,11 @@ grep 'require rsc.io/quote' go.mod
 
 cp go.mod.orig go.mod
 ! go get -d rsc.io/quote/x...
-stderr 'go get rsc.io/quote/x...: module rsc.io/quote@upgrade \(v1.5.2\) found, but does not contain packages matching rsc.io/quote/x...'
+stderr 'go get rsc.io/quote/x...: module rsc.io/quote@upgrade found \(v1.5.2\), but does not contain packages matching rsc.io/quote/x...'
 ! grep 'require rsc.io/quote' go.mod
 
 ! go get -d rsc.io/quote/x/...
-stderr 'go get rsc.io/quote/x/...: module rsc.io/quote@upgrade \(v1.5.2\) found, but does not contain packages matching rsc.io/quote/x/...'
+stderr 'go get rsc.io/quote/x/...: module rsc.io/quote@upgrade found \(v1.5.2\), but does not contain packages matching rsc.io/quote/x/...'
 ! grep 'require rsc.io/quote' go.mod
 
 # If a pattern matches no packages within a module, the module should not

src/cmd/go/testdata/script/mod_replace.txt

@@ -38,6 +38,13 @@ grep 'not-rsc.io/quote/v3 v3.1.0' go.mod
 exec ./a5.exe
 stdout 'Concurrency is not parallelism.'
 
+# Error messages for modules not found in replacements should
+# indicate the replacement module.
+cp go.mod.orig go.mod
+go mod edit -replace=rsc.io/quote/v3=./local/rsc.io/quote/v3
+! go get -d rsc.io/quote/v3/missing-package
+stderr 'module rsc.io/quote/v3@upgrade found \(v3.0.0, replaced by ./local/rsc.io/quote/v3\), but does not contain package'
+
 -- go.mod --
 module quoter