fix: Deduplicate attribute diagnostics

Author: radeksimko

internal/backend/local/backend_plan.go

@@ -76,8 +76,7 @@ func (b *Local) opPlan(
 		b.ContextOpts = new(terraform.ContextOpts)
 	}
 
-	// Get our context
-	// first diagnostic
+	// Set up backend and get our context
 	lr, configSnap, opState, ctxDiags := b.localRun(op)
 	diags = diags.Append(ctxDiags)
 	if ctxDiags.HasErrors() {
@@ -106,7 +105,6 @@ func (b *Local) opPlan(
 		defer logging.PanicHandler()
 		defer close(doneCh)
 		log.Printf("[INFO] backend/local: plan calling Plan")
-		// second diagnostic
 		plan, planDiags = lr.Core.Plan(lr.Config, lr.InputState, lr.PlanOpts)
 	}()
 
@@ -122,7 +120,7 @@ func (b *Local) opPlan(
 	// NOTE: We intentionally don't stop here on errors because we always want
 	// to try to present a partial plan report and, if the user chose to,
 	// generate a partial saved plan file for external analysis.
-	diags = planDiags
+	diags = diags.AppendWithoutDuplicates(planDiags...)
 
 	// Even if there are errors we need to handle anything that may be
 	// contained within the plan, so only exit if there is no data at all.

internal/tfdiags/compare.go

@@ -20,18 +20,15 @@ var DiagnosticComparer cmp.Option = cmp.Comparer(diagnosticComparerSimple)
 // diagnosticComparerSimple returns false when a difference is identified between
 // the two Diagnostic arguments.
 func diagnosticComparerSimple(l, r Diagnostic) bool {
-	if l.Severity() != r.Severity() {
-		return false
-	}
-	if l.Description() != r.Description() {
+	ld, ok := l.(ComparableDiagnostic)
+	if !ok {
 		return false
 	}
 
-	// Do the diagnostics originate from the same attribute name, if any?
-	lp := GetAttribute(l)
-	rp := GetAttribute(r)
-	if len(lp) != len(rp) {
+	rd, ok := r.(ComparableDiagnostic)
+	if !ok {
 		return false
 	}
-	return lp.Equals(rp)
+
+	return ld.Equals(rd)
 }

internal/tfdiags/contextual.go

@@ -205,6 +205,26 @@ func (d *attributeDiagnostic) ElaborateFromConfigBody(body hcl.Body, addr string
 	return &ret
 }
 
+func (d *attributeDiagnostic) Equals(otherDiag ComparableDiagnostic) bool {
+	od, ok := otherDiag.(*attributeDiagnostic)
+	if !ok {
+		return false
+	}
+	if d.severity != od.severity {
+		return false
+	}
+	if d.summary != od.summary {
+		return false
+	}
+	if d.detail != od.detail {
+		return false
+	}
+	if d.address != od.address {
+		return false
+	}
+	return d.attrPath.Equals(od.attrPath)
+}
+
 func traversePathSteps(traverse []cty.PathStep, body hcl.Body) hcl.Body {
 	for i := 0; i < len(traverse); i++ {
 		step := traverse[i]

internal/tfdiags/diagnostic.go

@@ -27,6 +27,10 @@ type Diagnostic interface {
 	ExtraInfo() interface{}
 }
 
+type ComparableDiagnostic interface {
+	Equals(otherDiag ComparableDiagnostic) bool
+}
+
 type Severity rune
 
 //go:generate go tool golang.org/x/tools/cmd/stringer -type=Severity

internal/tfdiags/diagnostics.go

@@ -83,6 +83,41 @@ func (diags Diagnostics) Append(new ...interface{}) Diagnostics {
 	return diags
 }
 
+func (diags Diagnostics) ContainsDiagnostic(diag ComparableDiagnostic) bool {
+	for _, d := range diags {
+		if cd, ok := d.(ComparableDiagnostic); ok && diag.Equals(cd) {
+			return true
+		}
+	}
+	return false
+}
+
+func (diags Diagnostics) AppendWithoutDuplicates(newDiags ...Diagnostic) Diagnostics {
+	for _, newItem := range newDiags {
+		if newItem == nil {
+			continue
+		}
+
+		cd, ok := newItem.(ComparableDiagnostic)
+		if !ok {
+			// append what we cannot compare
+			diags = diags.Append(newItem)
+		}
+
+		if diags.ContainsDiagnostic(cd) {
+			continue
+		}
+
+		diags = diags.Append(newItem)
+	}
+
+	if len(diags) == 0 {
+		return nil
+	}
+
+	return diags
+}
+
 func diagnosticsForError(err error) []Diagnostic {
 	if err == nil {
 		return nil