completion: Don't show builtins on default rules (#1056)

Related to #1010

Signed-off-by: Charlie Egan <charlie@styra.com>

internal/lsp/completions/providers/builtins.go

@@ -29,6 +29,11 @@ func (*BuiltIns) Run(c *cache.Cache, params types.CompletionParams, _ *Options)
 		return []types.CompletionItem{}, nil
 	}
 
+	// default rules cannot contain calls
+	if strings.HasPrefix(strings.TrimSpace(currentLine), "default ") {
+		return []types.CompletionItem{}, nil
+	}
+
 	words := patternWhiteSpace.Split(strings.TrimSpace(currentLine), -1)
 	lastWord := words[len(words)-1]
 
@@ -47,30 +52,32 @@ func (*BuiltIns) Run(c *cache.Cache, params types.CompletionParams, _ *Options)
 			continue
 		}
 
-		if strings.HasPrefix(key, lastWord) {
-			items = append(items, types.CompletionItem{
-				Label:  key,
-				Kind:   completion.Function,
-				Detail: "built-in function",
-				Documentation: &types.MarkupContent{
-					Kind:  "markdown",
-					Value: hover.CreateHoverContent(builtIn),
-				},
-				TextEdit: &types.TextEdit{
-					Range: types.Range{
-						Start: types.Position{
-							Line:      params.Position.Line,
-							Character: params.Position.Character - uint(len(lastWord)),
-						},
-						End: types.Position{
-							Line:      params.Position.Line,
-							Character: params.Position.Character,
-						},
+		if !strings.HasPrefix(key, lastWord) {
+			continue
+		}
+
+		items = append(items, types.CompletionItem{
+			Label:  key,
+			Kind:   completion.Function,
+			Detail: "built-in function",
+			Documentation: &types.MarkupContent{
+				Kind:  "markdown",
+				Value: hover.CreateHoverContent(builtIn),
+			},
+			TextEdit: &types.TextEdit{
+				Range: types.Range{
+					Start: types.Position{
+						Line:      params.Position.Line,
+						Character: params.Position.Character - uint(len(lastWord)),
+					},
+					End: types.Position{
+						Line:      params.Position.Line,
+						Character: params.Position.Character,
 					},
-					NewText: key,
 				},
-			})
-		}
+				NewText: key,
+			},
+		})
 	}
 
 	return items, nil

internal/lsp/completions/providers/builtins_test.go

@@ -184,6 +184,39 @@ allow if c`
 	}
 }
 
+func TestBuiltIns_noDefaultRule(t *testing.T) {
+	t.Parallel()
+
+	c := cache.NewCache()
+
+	fileContents := `package foo
+
+default allow := f`
+
+	c.SetFileContents(testCaseFileURI, fileContents)
+
+	p := &BuiltIns{}
+
+	completionParams := types.CompletionParams{
+		TextDocument: types.TextDocumentIdentifier{
+			URI: testCaseFileURI,
+		},
+		Position: types.Position{
+			Line:      2,
+			Character: 18, // is the c char that triggered the request
+		},
+	}
+
+	completions, err := p.Run(c, completionParams, nil)
+	if err != nil {
+		t.Fatalf("Unexpected error: %v", err)
+	}
+
+	if len(completions) != 0 {
+		t.Fatalf("Expected no completions, got: %d", len(completions))
+	}
+}
+
 func completionLabels(completions []types.CompletionItem) []string {
 	labels := make([]string, len(completions))
 	for i, c := range completions {