fix: correct bug with broken semantic tokens request (#20)

Author: owenrumney

lsp/capabilities.go

@@ -264,16 +264,61 @@ type FoldingRangeClientCapabilities struct {
 
 // SemanticTokensClientCapabilities declares which semantic token types, modifiers, and request styles (full, delta, range) the editor supports.
 type SemanticTokensClientCapabilities struct {
-	DynamicRegistration *bool `json:"dynamicRegistration,omitempty"`
-	Requests            struct {
-		Range *bool               `json:"range,omitempty"`
-		Full  *SemanticTokensFull `json:"full,omitempty"`
-	} `json:"requests"`
-	TokenTypes              []string      `json:"tokenTypes"`
-	TokenModifiers          []string      `json:"tokenModifiers"`
-	Formats                 []TokenFormat `json:"formats"`
-	OverlappingTokenSupport *bool         `json:"overlappingTokenSupport,omitempty"`
-	MultilineTokenSupport   *bool         `json:"multilineTokenSupport,omitempty"`
+	DynamicRegistration     *bool                              `json:"dynamicRegistration,omitempty"`
+	Requests                SemanticTokensRequestsCapabilities `json:"requests"`
+	TokenTypes              []string                           `json:"tokenTypes"`
+	TokenModifiers          []string                           `json:"tokenModifiers"`
+	Formats                 []TokenFormat                      `json:"formats"`
+	OverlappingTokenSupport *bool                              `json:"overlappingTokenSupport,omitempty"`
+	MultilineTokenSupport   *bool                              `json:"multilineTokenSupport,omitempty"`
+}
+
+// SemanticTokensRequestsCapabilities describes the semantic token request styles the client supports.
+// Per the LSP spec, "range" is `boolean | {}` and "full" is `boolean | { delta?: boolean }`;
+// UnmarshalJSON accepts either form.
+type SemanticTokensRequestsCapabilities struct {
+	Range *bool               `json:"range,omitempty"`
+	Full  *SemanticTokensFull `json:"full,omitempty"`
+}
+
+// UnmarshalJSON accepts both the boolean and object forms for "range" and "full" per the LSP spec.
+func (s *SemanticTokensRequestsCapabilities) UnmarshalJSON(data []byte) error {
+	var raw struct {
+		Range json.RawMessage `json:"range"`
+		Full  json.RawMessage `json:"full"`
+	}
+	if err := json.Unmarshal(data, &raw); err != nil {
+		return err
+	}
+
+	if len(raw.Range) > 0 && string(raw.Range) != "null" {
+		var b bool
+		if err := json.Unmarshal(raw.Range, &b); err == nil {
+			s.Range = &b
+		} else {
+			// Empty object form ({}) — presence indicates support.
+			t := true
+			s.Range = &t
+		}
+	}
+
+	if len(raw.Full) > 0 && string(raw.Full) != "null" {
+		var b bool
+		if err := json.Unmarshal(raw.Full, &b); err == nil {
+			if b {
+				s.Full = &SemanticTokensFull{}
+			}
+			// false → leave Full nil to signal unsupported.
+		} else {
+			var f SemanticTokensFull
+			if err := json.Unmarshal(raw.Full, &f); err != nil {
+				return err
+			}
+			s.Full = &f
+		}
+	}
+
+	return nil
 }
 
 // WindowClientCapabilities declares editor support for window features like work-done progress, show-message requests, and show-document.

lsp/lsp_test.go

@@ -157,6 +157,86 @@ func TestServerCapabilitiesMarshal(t *testing.T) {
 	}
 }
 
+func TestSemanticTokensRequestsUnmarshal(t *testing.T) {
+	tests := []struct {
+		name    string
+		input   string
+		check   func(t *testing.T, r SemanticTokensRequestsCapabilities)
+		wantErr bool
+	}{
+		{
+			name:  "full as true",
+			input: `{"requests":{"full":true}}`,
+			check: func(t *testing.T, r SemanticTokensRequestsCapabilities) {
+				if r.Full == nil {
+					t.Fatal("full should be non-nil for boolean true")
+				}
+				if r.Full.Delta != nil {
+					t.Errorf("delta should be nil, got %v", *r.Full.Delta)
+				}
+			},
+		},
+		{
+			name:  "full as false",
+			input: `{"requests":{"full":false}}`,
+			check: func(t *testing.T, r SemanticTokensRequestsCapabilities) {
+				if r.Full != nil {
+					t.Errorf("full should be nil for boolean false, got %+v", r.Full)
+				}
+			},
+		},
+		{
+			name:  "full as object with delta",
+			input: `{"requests":{"full":{"delta":true}}}`,
+			check: func(t *testing.T, r SemanticTokensRequestsCapabilities) {
+				if r.Full == nil || r.Full.Delta == nil || !*r.Full.Delta {
+					t.Fatalf("delta not preserved, got %+v", r.Full)
+				}
+			},
+		},
+		{
+			name:  "range as boolean",
+			input: `{"requests":{"range":true}}`,
+			check: func(t *testing.T, r SemanticTokensRequestsCapabilities) {
+				if r.Range == nil || !*r.Range {
+					t.Fatalf("range not preserved, got %+v", r.Range)
+				}
+			},
+		},
+		{
+			name:  "range as empty object",
+			input: `{"requests":{"range":{}}}`,
+			check: func(t *testing.T, r SemanticTokensRequestsCapabilities) {
+				if r.Range == nil || !*r.Range {
+					t.Fatalf("range {} should mean supported, got %+v", r.Range)
+				}
+			},
+		},
+		{
+			name:    "full as invalid",
+			input:   `{"requests":{"full":"nonsense"}}`,
+			wantErr: true,
+		},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			var caps SemanticTokensClientCapabilities
+			err := json.Unmarshal([]byte(tc.input), &caps)
+			if tc.wantErr {
+				if err == nil {
+					t.Fatal("expected error, got nil")
+				}
+				return
+			}
+			if err != nil {
+				t.Fatalf("unmarshal: %v", err)
+			}
+			tc.check(t, caps.Requests)
+		})
+	}
+}
+
 func TestPositionEncodingCapabilitiesMarshal(t *testing.T) {
 	caps := ClientCapabilities{
 		General: &GeneralClientCapabilities{