status: Add projectConstraint & constraintsCollection

The resultant collection obtained from collectConstraints() should
contain data about which project set a particular constraint on a
dependency project. `projectConstraint` consists of the project and the
constraint it sets on a given dependency.

And `constraintsCollection` is a map to store the pair of dependency project
and a collection of `projectConstraint` for different constraints.

This would be used by project argument status (status for a single project),
to show the importers of the project.

cmd/dep/status.go

@@ -460,7 +460,7 @@ func runStatusAll(ctx *dep.Ctx, out outputter, p *dep.Project, sm gps.SourceMana
 				} else {
 					bs.Constraint = gps.Any()
 					for _, c := range cm[bs.ProjectRoot] {
-						bs.Constraint = c.Intersect(bs.Constraint)
+						bs.Constraint = c.Constraint.Intersect(bs.Constraint)
 					}
 				}
 
@@ -643,9 +643,20 @@ func formatVersion(v gps.Version) string {
 	return v.String()
 }
 
+// projectConstraint stores ProjectRoot and Constraint for that project.
+type projectConstraint struct {
+	Project    gps.ProjectRoot
+	Constraint gps.Constraint
+}
+
+// constraintsCollection is a map of ProjectRoot(dependency) and a collection of
+// projectConstraint for the dependencies. This can be used to find constraints
+// on a dependency and the projects that apply those constraints.
+type constraintsCollection map[string][]projectConstraint
+
 // collectConstraints collects constraints declared by all the dependencies.
-func collectConstraints(ctx *dep.Ctx, p *dep.Project, sm gps.SourceManager) map[string][]gps.Constraint {
-	constraintCollection := make(map[string][]gps.Constraint)
+func collectConstraints(ctx *dep.Ctx, p *dep.Project, sm gps.SourceManager) constraintsCollection {
+	constraintCollection := make(constraintsCollection)
 
 	// Get direct deps of the root project.
 	_, directDeps, err := getDirectDependencies(sm, p)
@@ -669,7 +680,10 @@ func collectConstraints(ctx *dep.Ctx, p *dep.Project, sm gps.SourceManager) map[
 		// Iterate through the project constraints to get individual dependency
 		// project and constraint values.
 		for pr, pp := range pc {
-			constraintCollection[string(pr)] = append(constraintCollection[string(pr)], pp.Constraint)
+			constraintCollection[string(pr)] = append(
+				constraintCollection[string(pr)],
+				projectConstraint{proj.Ident().ProjectRoot, pp.Constraint},
+			)
 		}
 	}
 

cmd/dep/status_test.go

@@ -300,7 +300,7 @@ func TestCollectConstraints(t *testing.T) {
 	cases := []struct {
 		name            string
 		project         dep.Project
-		wantConstraints map[string][]gps.Constraint
+		wantConstraints constraintsCollection
 	}{
 		{
 			name: "without any constraints",
@@ -315,7 +315,7 @@ func TestCollectConstraints(t *testing.T) {
 					},
 				},
 			},
-			wantConstraints: map[string][]gps.Constraint{},
+			wantConstraints: constraintsCollection{},
 		},
 		{
 			name: "with multiple constraints",
@@ -340,10 +340,17 @@ func TestCollectConstraints(t *testing.T) {
 					},
 				},
 			},
-			wantConstraints: map[string][]gps.Constraint{
-				"github.com/sdboyer/deptest":    []gps.Constraint{ver1, ver08},
-				"github.com/sdboyer/deptestdos": []gps.Constraint{ver2},
-				"github.com/sdboyer/dep-test":   []gps.Constraint{ver1},
+			wantConstraints: constraintsCollection{
+				"github.com/sdboyer/deptest": []projectConstraint{
+					{"github.com/darkowlzz/deptest-project-1", ver1},
+					{"github.com/darkowlzz/deptest-project-2", ver08},
+				},
+				"github.com/sdboyer/deptestdos": []projectConstraint{
+					{"github.com/darkowlzz/deptest-project-2", ver2},
+				},
+				"github.com/sdboyer/dep-test": []projectConstraint{
+					{"github.com/darkowlzz/deptest-project-2", ver1},
+				},
 			},
 		},
 		{
@@ -364,8 +371,10 @@ func TestCollectConstraints(t *testing.T) {
 					},
 				},
 			},
-			wantConstraints: map[string][]gps.Constraint{
-				"github.com/sdboyer/deptest": []gps.Constraint{ver1},
+			wantConstraints: constraintsCollection{
+				"github.com/sdboyer/deptest": []projectConstraint{
+					{"github.com/darkowlzz/deptest-project-1", ver1},
+				},
 			},
 		},
 	}