internal/frontend: redirect on "std/" queries

If a search query is "std/P", where P is a a stdlib package, redirect
to P without searching.

Also, update the help page on search to mention this, and to correctly
reflect the existing behavior of always doing a search for queries
without a slash.

For golang/go#71452.

Change-Id: Idf5c09ee3e81b4c6efa44c2d76470e6f496dcbcd
Reviewed-on: https://go-review.googlesource.com/c/pkgsite/+/644676
kokoro-CI: kokoro <[email protected]>
Reviewed-by: Robert Findley <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>

Author: jba

internal/frontend/search.go

@@ -344,7 +344,8 @@ func newSearchResult(r *internal.SearchResult, searchSymbols bool, pr *message.P
 // If the user types an existing package path into the search bar, we will
 // redirect the user to the details page. Standard library packages that only
 // contain one element (such as fmt, errors, etc.) will not redirect, to allow
-// users to search by those terms.
+// users to search by those terms. However, if the query begins with "std/" and
+// then contains a stdlib package, even a one-element one, then it will be redirected.
 //
 // If the user types a name that is in the form of a Go vulnerability ID, we will
 // redirect to the page for that ID (whether or not it exists).
@@ -360,6 +361,10 @@ func searchRequestRedirectPath(ctx context.Context, ds internal.DataSource, quer
 	if !strings.Contains(requestedPath, "/") || mode == searchModeVuln {
 		return ""
 	}
+	if path, ok := strings.CutPrefix(requestedPath, "std/"); ok && stdlib.Contains(path) {
+		requestedPath = path
+	}
+
 	_, err := ds.GetUnitMeta(ctx, requestedPath, internal.UnknownModulePath, version.Latest)
 	if err != nil {
 		if !errors.Is(err, derrors.NotFound) {

internal/frontend/search_test.go

@@ -533,10 +533,12 @@ func TestSearchRequestRedirectPath(t *testing.T) {
 		{"module", "golang.org/x/tools", "/golang.org/x/tools", ""},
 		{"directory", "golang.org/x/tools/internal", "/golang.org/x/tools/internal", ""},
 		{"package", "golang.org/x/tools/internal/lsp", "/golang.org/x/tools/internal/lsp", ""},
-		{"stdlib package does not redirect", "errors", "", ""},
+		{"stdlib package does not redirect", "fmt", "", ""},
 		{"stdlib package does redirect", "cmd/go", "/cmd/go", ""},
 		{"stdlib directory does redirect", "cmd/go/internal", "/cmd/go/internal", ""},
 		{"std does not redirect", "std", "", ""},
+		{"std/stdlib-package does redirect", "std/fmt", "/fmt", ""},
+		{"std/other-package does not redirect", "std/golang.org/x/tools", "", ""},
 		{"non-existent path does not redirect", "github.com/non-existent", "", ""},
 		{"trim URL scheme from query", "https://golang.org/x/tools", "/golang.org/x/tools", ""},
 		{"Go vuln redirects", "GO-1969-0720", "/vuln/GO-1969-0720?q", ""},

static/frontend/search-help/search-help.tmpl

@@ -17,7 +17,12 @@
         <p>You can search for packages in which the search text occurs in the package name, package path, synopsis, or README.</p>
         <p>Results are grouped by module, displaying the most relevant package in each module.</p>
         <p>You can also search for a package by its full or partial import path.</p>
-        <p>If the package path you specified is complete enough, matching a full package import path, you will be brought directly to the details page for the latest version of that package.</p>
+        <p>If the package path you specified contains a slash and matches a full package import path,
+        you will be brought directly to the details page for the latest version of that package.
+        As a special case, a standard library package preceded by "std/" will also redirect to the package.
+        For example, "path" conducts a search for "path", but "std/path" redirects to the "path" package.
+        </p>
+
         <h2>Searching by symbol</h2>
         <p>You can also search for a symbol by name across all packages. A symbol is a constant, variable, function, type, field, or method.</p>
         <p>Searching by symbol will return a list of packages containing the symbol you specify. You can search by the following:</p>