testing: fix construction of the testing artifacts path

The existing implementation had a few problems:
- It constructs a path which starts with a forward slash, which is
then immediately rejected by filepath.Localize() as invalid.
- It did not correctly remove the module path from the import path if
the test was in the root package of the module: it would do the
equivalent of strings.TrimPrefix("example.com/jdoe/loader",
"example.com/jdoe/loader/"), which trims nothing, and leaves the full
module name in the base.
- Tests didn't check for any behaviors related to which artifact path
was selected.

Removed leading slash, handle tests in the root package by omitting the
<pkg> component from the artifact dir path, and add tests.

Fixes #77763

Change-Id: I00fc7381b939e4d8a8a9811e2a95fc2d8c5a6e84
GitHub-Last-Rev: 9c39392a691a81cef48adde88ab45dc40ed81105
GitHub-Pull-Request: golang/go#77778
Reviewed-on: https://go-review.googlesource.com/c/go/+/748581
Auto-Submit: Damien Neil <dneil@google.com>
Reviewed-by: Damien Neil <dneil@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>

1 files changed, 26 insertions, 16 deletions

diff --git a/src/testing/testing.go b/src/testing/testing.go
index 34b45b41b9..bf95f1cfbb 100644
--- a/src/testing/testing.go
+++ b/src/testing/testing.go
@@ -1363,6 +1363,21 @@ func (c *common) makeArtifactDir() (string, error) {
 		return c.makeTempDir()
 	}
 
+	artifactBase := filepath.Join(artifactDir, c.relativeArtifactBase())
+	if err := os.MkdirAll(artifactBase, 0o777); err != nil {
+		return "", err
+	}
+	dir, err := os.MkdirTemp(artifactBase, "")
+	if err != nil {
+		return "", err
+	}
+	if c.chatty != nil {
+		c.chatty.Updatef(c.name, "=== ARTIFACTS %s %v\n", c.name, dir)
+	}
+	return dir, nil
+}
+
+func (c *common) relativeArtifactBase() string {
 	// If the test name is longer than maxNameSize, truncate it and replace the last
 	// hashSize bytes with a hash of the full name.
 	const maxNameSize = 64
@@ -1373,11 +1388,17 @@ func (c *common) makeArtifactDir() (string, error) {
 	}
 
 	// Remove the module path prefix from the import path.
-	pkg := strings.TrimPrefix(c.importPath, c.modulePath+"/")
+	// If this is the root package, pkg will be empty.
+	pkg := strings.TrimPrefix(c.importPath, c.modulePath)
+	// Remove the leading slash.
+	pkg = strings.TrimPrefix(pkg, "/")
 
-	// Join with /, not filepath.Join: the import path is /-separated,
-	// and we don't want removeSymbolsExcept to strip \ separators on Windows.
-	base := "/" + pkg + "/" + name
+	base := name
+	if pkg != "" {
+		// Join with /, not filepath.Join: the import path is /-separated,
+		// and we don't want removeSymbolsExcept to strip \ separators on Windows.
+		base = pkg + "/" + name
+	}
 	base = removeSymbolsExcept(base, "!#$%&()+,-.=@^_{}~ /")
 	base, err := filepath.Localize(base)
 	if err != nil {
@@ -1386,18 +1407,7 @@ func (c *common) makeArtifactDir() (string, error) {
 		base = ""
 	}
 
-	artifactBase := filepath.Join(artifactDir, base)
-	if err := os.MkdirAll(artifactBase, 0o777); err != nil {
-		return "", err
-	}
-	dir, err := os.MkdirTemp(artifactBase, "")
-	if err != nil {
-		return "", err
-	}
-	if c.chatty != nil {
-		c.chatty.Updatef(c.name, "=== ARTIFACTS %s %v\n", c.name, dir)
-	}
-	return dir, nil
+	return base
 }
 
 func removeSymbolsExcept(s, allowed string) string {