Move LSP semantics into typed analysis

internal/lang/diagnostics.go

@@ -0,0 +1,50 @@
+package lang
+
+import (
+	"fmt"
+	"regexp"
+	"strconv"
+)
+
+type DiagnosticSeverity int
+
+const (
+	DiagnosticError   DiagnosticSeverity = 1
+	DiagnosticWarning DiagnosticSeverity = 2
+)
+
+type SourceSpan struct {
+	Start int
+	End   int
+}
+
+type SemanticDiagnostic struct {
+	Code     string
+	Message  string
+	Severity DiagnosticSeverity
+	Span     SourceSpan
+}
+
+func (diagnostic SemanticDiagnostic) Error() string { return diagnostic.Message }
+
+var semanticOffsetPattern = regexp.MustCompile(`\sat\s(\d+)$`)
+
+func diagnosticForError(code string, err error) SemanticDiagnostic {
+	span := SourceSpan{}
+	if match := semanticOffsetPattern.FindStringSubmatch(err.Error()); len(match) == 2 {
+		if offset, parseErr := strconv.Atoi(match[1]); parseErr == nil {
+			span = SourceSpan{Start: offset, End: offset + 1}
+		}
+	}
+	return SemanticDiagnostic{Code: code, Message: err.Error(), Severity: DiagnosticError, Span: span}
+}
+
+func undefinedDiagnostic(name string, position int) SemanticDiagnostic {
+	end := position + len(name)
+	return SemanticDiagnostic{
+		Code:     "undefined-symbol",
+		Message:  fmt.Sprintf("undefined identifier %s", name),
+		Severity: DiagnosticError,
+		Span:     SourceSpan{Start: position, End: end},
+	}
+}