fix(sidekick): retain trailing resource names containing intermediate literals (#4621)

Previously, the backward-scanning loop assumed that every path segment
preceding a known `collection/variable` pair had to be another variable.
If it encountered an unpacked string literal like `global` in the path
`/projects/{project}/global/backendServices/{backend_service}`, it broke
the chain early.

The loop now explicitly handle two distinct cases:
Case 1 (Standalone Literal): If the preceding path segment is a
standalone literal string (that isn't an API version like `v1`), the
scanner steps past it instead of breaking.
Case 2 (Variable + Literal Pair): Normal lookup and matching of
`collection/variable` pairs like `projects` and `{project}`.

Fixes #4620

Author: haphungw

internal/sidekick/api/resource_identification.go

@@ -99,21 +99,42 @@ func identifyHeuristicTarget(method *Method, binding *PathBinding, vocabulary ma
 		// beginning of a resource pattern chain.
 		firstIndex := i
 		if vocabulary[token] {
-			// Walk backwards to find the start of the (literal, variable) chain
+			// Walk backwards to find the start of the resource pattern chain
 			firstIndex = i - 1
-			for firstIndex >= 2 {
-				if tmpl.Segments[firstIndex-1].Variable == nil || tmpl.Segments[firstIndex-2].Literal == nil {
-					break
+			for firstIndex > 0 {
+				prevSeg := tmpl.Segments[firstIndex-1]
+
+				// Case 1: The preceding segment is a standalone literal (e.g., "global")
+				if prevSeg.Literal != nil {
+					if isVersionString(*prevSeg.Literal) {
+						break // Stop at version strings (e.g., "v1")
+					}
+					firstIndex--
+					continue
 				}
-				// Stop matching if the preceding segment isn't a known collection.
-				if !vocabulary[*tmpl.Segments[firstIndex-2].Literal] {
-					// Include root-level resource variables immediately after version string.
-					if isVersionString(*tmpl.Segments[firstIndex-2].Literal) {
-						firstIndex -= 1
+
+				// Case 2: The preceding segment is a variable. It must be paired with a literal.
+				if prevSeg.Variable != nil {
+					if firstIndex < 2 || tmpl.Segments[firstIndex-2].Literal == nil {
+						break // Variable near the beginning, cannot form a pair
+					}
+
+					prevLiteralVal := *tmpl.Segments[firstIndex-2].Literal
+
+					// If the literal is a known collection, include the pair and continue
+					if vocabulary[prevLiteralVal] {
+						firstIndex -= 2
+						continue
 					}
+
+					// If the literal is a version string, include the variable but stop here
+					if isVersionString(prevLiteralVal) {
+						firstIndex--
+					}
+
+					// The chain is broken, so stop scanning.
 					break
 				}
-				firstIndex -= 2
 			}
 		}
 

internal/sidekick/api/resource_identification_test.go

@@ -266,7 +266,53 @@ func TestIdentifyTargetResources_Heuristic(t *testing.T) {
 				Template:   ParseTemplateForTest("//test-api.googleapis.com/projects/{project}/zones/{zone}/instances/{instance}"),
 			},
 		},
-
+		{
+			name:      "heuristic: paths with standalone literals without variables (e.g. global)",
+			serviceID: ".google.cloud.compute.v1.BackendServices",
+			path: NewPathTemplate().
+				WithLiteral("projects").WithVariableNamed("project").
+				WithLiteral("global").
+				WithLiteral("backendServices").WithVariableNamed("backend_service"),
+			fields: []*Field{
+				{Name: "project", Typez: STRING_TYPE},
+				{Name: "backend_service", Typez: STRING_TYPE},
+			},
+			getPaths: []*PathTemplate{
+				NewPathTemplate().
+					WithLiteral("projects").WithVariableNamed("project").
+					WithLiteral("global").
+					WithLiteral("backendServices").WithVariableNamed("backend_service"),
+			},
+			want: &TargetResource{
+				FieldPaths: [][]string{{"project"}, {"backend_service"}},
+				Template:   ParseTemplateForTest("//test-api.googleapis.com/projects/{project}/global/backendServices/{backend_service}"),
+			},
+		},
+		{
+			name:      "heuristic: path with non-variable standalone literal",
+			serviceID: ".google.cloud.example.v1.Service",
+			path: NewPathTemplate().
+				WithLiteral("v1").
+				WithLiteral("projects").
+				WithLiteral("xyz").
+				WithLiteral("global").
+				WithLiteral("foos").WithVariableNamed("foo"),
+			fields: []*Field{
+				{Name: "foo", Typez: STRING_TYPE},
+			},
+			getPaths: []*PathTemplate{
+				NewPathTemplate().
+					WithLiteral("v1").
+					WithLiteral("projects").
+					WithLiteral("xyz").
+					WithLiteral("global").
+					WithLiteral("foos").WithVariableNamed("foo"),
+			},
+			want: &TargetResource{
+				FieldPaths: [][]string{{"foo"}},
+				Template:   ParseTemplateForTest("//test-api.googleapis.com/projects/xyz/global/foos/{foo}"),
+			},
+		},
 		{
 			name:      "heuristic: paths with un-grouped variable after version string",
 			serviceID: ".google.cloud.compute.v1.Instances",