cmd/go/internal/modload: eliminate QueryPackage

QueryPackage was a wrapper around QueryPattern with extra validation,
called only once from within the same package. Most of that validation
was already performed much earlier, in (*loader).Load. Inline the
remaining validation and remove the needless indirection.

For #36460

Change-Id: I108a01d416197db8f886889554e07b29f0c37f3f
Reviewed-on: https://go-review.googlesource.com/c/go/+/256057
Trust: Bryan C. Mills <bcmills@google.com>
Trust: Jay Conrod <jayconrod@google.com>
Run-TryBot: Bryan C. Mills <bcmills@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Michael Matloob <matloob@golang.org>
Reviewed-by: Jay Conrod <jayconrod@google.com>

src/cmd/go/internal/modload/import.go

@@ -261,7 +261,7 @@ func queryImport(ctx context.Context, path string) (module.Version, error) {
 		}
 
 		// Every module path in mods is a prefix of the import path.
-		// As in QueryPackage, prefer the longest prefix that satisfies the import.
+		// As in QueryPattern, prefer the longest prefix that satisfies the import.
 		sort.Slice(mods, func(i, j int) bool {
 			return len(mods[i].Path) > len(mods[j].Path)
 		})
@@ -300,9 +300,9 @@ func queryImport(ctx context.Context, path string) (module.Version, error) {
 		// in the build list, and isn't in any other module that the user has
 		// shimmed in via a "replace" directive.
 		// Moreover, the import path is reserved for the standard library, so
-		// QueryPackage cannot possibly find a module containing this package.
+		// QueryPattern cannot possibly find a module containing this package.
 		//
-		// Instead of trying QueryPackage, report an ImportMissingError immediately.
+		// Instead of trying QueryPattern, report an ImportMissingError immediately.
 		return module.Version{}, &ImportMissingError{Path: path}
 	}
 
@@ -321,11 +321,11 @@ func queryImport(ctx context.Context, path string) (module.Version, error) {
 	// and return m, dir, ImpportMissingError.
 	fmt.Fprintf(os.Stderr, "go: finding module for package %s\n", path)
 
-	candidates, err := QueryPackage(ctx, path, "latest", CheckAllowed)
+	candidates, err := QueryPattern(ctx, path, "latest", CheckAllowed)
 	if err != nil {
 		if errors.Is(err, os.ErrNotExist) {
 			// Return "cannot find module providing package […]" instead of whatever
-			// low-level error QueryPackage produced.
+			// low-level error QueryPattern produced.
 			return module.Version{}, &ImportMissingError{Path: path, QueryErr: err}
 		} else {
 			return module.Version{}, err
@@ -338,7 +338,7 @@ func queryImport(ctx context.Context, path string) (module.Version, error) {
 		canAdd := true
 		for _, bm := range buildList {
 			if bm.Path == cm.Path && semver.Compare(bm.Version, cm.Version) > 0 {
-				// QueryPackage proposed that we add module cm to provide the package,
+				// QueryPattern proposed that we add module cm to provide the package,
 				// but we already depend on a newer version of that module (and we don't
 				// have the package).
 				//

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

@@ -1018,6 +1018,14 @@ func (ld *loader) load(pkg *loadPkg) {
 		return
 	}
 
+	if search.IsMetaPackage(pkg.path) {
+		pkg.err = &invalidImportError{
+			importPath: pkg.path,
+			err:        fmt.Errorf("%q is not an importable package; see 'go help packages'", pkg.path),
+		}
+		return
+	}
+
 	pkg.mod, pkg.dir, pkg.err = importFromBuildList(context.TODO(), pkg.path)
 	if pkg.dir == "" {
 		return

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

@@ -431,20 +431,6 @@ type QueryResult struct {
 	Packages []string
 }
 
-// QueryPackage looks up the module(s) containing path at a revision matching
-// query. The results are sorted by module path length in descending order.
-//
-// If the package is in the main module, QueryPackage considers only the main
-// module and only the version "latest", without checking for other possible
-// modules.
-func QueryPackage(ctx context.Context, path, query string, allowed AllowedFunc) ([]QueryResult, error) {
-	m := search.NewMatch(path)
-	if m.IsLocal() || !m.IsLiteral() {
-		return nil, fmt.Errorf("pattern %s is not an importable package", path)
-	}
-	return QueryPattern(ctx, path, query, allowed)
-}
-
 // QueryPattern looks up the module(s) containing at least one package matching
 // the given pattern at the given version. The results are sorted by module path
 // length in descending order.

src/cmd/go/testdata/script/mod_import_issue41113.txt

@@ -5,7 +5,7 @@
 
 # Initially, our module depends on split-incompatible v2.1.0-pre+incompatible,
 # from which an imported package has been removed (and relocated to the nested
-# split-incompatible/subpkg module). modload.QueryPackage will suggest
+# split-incompatible/subpkg module). modload.QueryPattern will suggest
 # split-incompatible v2.0.0+incompatible, which we cannot use (because it would
 # be an implicit downgrade), and split-incompatible/subpkg v0.1.0, which we
 # *should* use.

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

@@ -0,0 +1,45 @@
+# The loader should not attempt to resolve imports of the "all", "std", and "cmd" meta-packages.
+
+! go list -deps ./importall
+! stderr 'internal error'
+stderr '^importall[/\\]x.go:3:8: "all" is not an importable package; see ''go help packages''$'
+
+! go list -deps ./importcmd
+! stderr 'internal error'
+stderr '^importcmd[/\\]x.go:3:8: "cmd" is not an importable package; see ''go help packages''$'
+
+! go list -deps ./importstd
+! stderr 'internal error'
+stderr '^importstd[/\\]x.go:3:8: "std" is not an importable package; see ''go help packages''$'
+
+
+# Not even if such a path is theoretically provided by a (necessarily replaced) module.
+
+go mod edit -replace std@v0.1.0=./modstd
+go mod edit -require std@v0.1.0
+
+! go list -deps ./importstd
+stderr '^importstd[/\\]x.go:3:8: "std" is not an importable package; see ''go help packages''$'
+
+
+-- go.mod --
+module example.com
+go 1.16
+-- importall/x.go --
+package importall
+
+import _ "all"
+-- importcmd/x.go --
+package importcmd
+
+import _ "cmd"
+-- importstd/x.go --
+package importstd
+
+import _ "std"
+-- modstd/go.mod --
+module std
+go 1.16
+-- modstd/std.go --
+// Package std is an incredibly confusingly-named package.
+package std