internal/code: support 12-character git hash module queries

Add support for 12-character lower-case git hash module queries.
This is a temporary workaround for golang.org/issue/32542; my intention
is to take it out when the upstream issue is resolved. /cc @heschik

Updates golang/go#32542

Author: dmitshur

internal/code/module.go

@@ -35,8 +35,10 @@ import (
 // versions from a VCS repository:
 //
 // • It serves only pseudo-versions derived from commits
-// on master branch. No other versions or module queries
-// are supported at this time.
+// on master branch. Temporarily, it also supports module
+// queries that are 12-character lower-case commit hashes.
+// No other versions or module queries are supported at
+// this time.
 //
 // • It serves a single module corresponding to the root
 // of each repository. Multi-module repositories are not
@@ -84,6 +86,35 @@ func (h ModuleHandler) ServeModule(w http.ResponseWriter, req *http.Request) err
 		return h.serveList(req.Context(), w, gitDir)
 	}
 
+	// Handle "/@v/<12-character git hash>.info" module queries.
+	// This is a temporary workaround for golang.org/issue/32542.
+	// TODO: Remove this once upstream issue is resolved.
+	if typ == "info" && len(version) == 12 && mod.AllHex(version) {
+		// Open the git repository and get the commit that corresponds to the hash.
+		repo, err := git.Open(gitDir)
+		if err != nil {
+			return err
+		}
+		defer func() {
+			if err := repo.Close(); err != nil {
+				log.Println("ModuleHandler.ServeModule: repo.Close:", err)
+			}
+		}()
+		commitID, err := repo.ResolveRevision(version)
+		if err != nil {
+			return os.ErrNotExist
+		}
+		commit, err := repo.GetCommit(commitID)
+		if err != nil || commit.Committer == nil {
+			return os.ErrNotExist
+		}
+
+		// Construct the canonical pseudo-version for this commit, and serve its info.
+		t := time.Unix(commit.Committer.Date.Seconds, 0).UTC()
+		pseudoVersion := mod.PseudoVersion("", "", t, string(commit.ID)[:12])
+		return h.serveInfo(w, pseudoVersion, t)
+	}
+
 	// Parse the time and revision from the pseudo-version.
 	versionTime, versionRevision, err := mod.ParsePseudoVersion(version)
 	if err != nil || len(versionRevision) != 12 || !mod.AllHex(versionRevision) {

internal/code/module_test.go

@@ -61,6 +61,15 @@ v0.0.0-20170914162131-bf160e40a791
 	"Version": "v0.0.0-20170912031248-a1d95f8919b5",
 	"Time": "2017-09-12T03:12:48Z"
 }
+`,
+		},
+		{
+			url:      "/api/module/dmitri.shuralyov.com/kebabcase/@v/a1d95f8919b5.info",
+			wantType: "application/json",
+			wantBody: `{
+	"Version": "v0.0.0-20170912031248-a1d95f8919b5",
+	"Time": "2017-09-12T03:12:48Z"
+}
 `,
 		},
 		{
@@ -70,6 +79,15 @@ v0.0.0-20170914162131-bf160e40a791
 	"Version": "v0.0.0-20170914162131-bf160e40a791",
 	"Time": "2017-09-14T16:21:31Z"
 }
+`,
+		},
+		{
+			url:      "/api/module/dmitri.shuralyov.com/kebabcase/@v/bf160e40a791.info",
+			wantType: "application/json",
+			wantBody: `{
+	"Version": "v0.0.0-20170914162131-bf160e40a791",
+	"Time": "2017-09-14T16:21:31Z"
+}
 `,
 		},
 		{