Add syntax error tests for FOR loops and COLLECT statements: enhance diagnostics for missing values, incomplete clauses, and unexpected syntax to improve error handling and clarity.

pkg/compiler/internal/diagnostics/helpers.go

@@ -110,10 +110,26 @@ func is(node *TokenNode, expected string) bool {
 	return strings.ToUpper(node.GetText()) == expected
 }
 
+func anyIs(first, second *TokenNode, expected string) *TokenNode {
+	if is(first, expected) {
+		return first
+	}
+
+	if is(second, expected) {
+		return second
+	}
+
+	return nil
+}
+
 func has(msg string, substr string) bool {
 	return strings.Contains(strings.ToLower(msg), strings.ToLower(substr))
 }
 
+func isMismatched(msg string) bool {
+	return has(msg, "mismatched input")
+}
+
 func isNoAlternative(msg string) bool {
 	return has(msg, "no viable alternative at input")
 }

pkg/compiler/internal/diagnostics/match_assignment_errors.go

@@ -13,11 +13,11 @@ func matchMissingAssignmentValue(src *file.Source, err *CompilationError, offend
 
 	prev := offending.Prev()
 
-	if is(offending, "LET") || is(prev, "=") {
-		span := spanFromTokenSafe(prev.Token(), src)
+	if node := anyIs(offending, prev, "="); node != nil {
+		span := spanFromTokenSafe(node.Token(), src)
 		span.Start++
 		span.End++
-		err.Message = fmt.Sprintf("Expected expression after '=' for variable '%s'", prev.Prev())
+		err.Message = fmt.Sprintf("Expected expression after '=' for variable '%s'", node.Prev())
 		err.Hint = "Did you forget to provide a value?"
 		err.Spans = []ErrorSpan{
 			NewMainErrorSpan(span, "missing value"),
@@ -26,5 +26,18 @@ func matchMissingAssignmentValue(src *file.Source, err *CompilationError, offend
 		return true
 	}
 
+	if is(offending, "LET") {
+		span := spanFromTokenSafe(offending.Token(), src)
+		span.Start = span.End
+		span.End = span.Start + 1
+		err.Message = "Expected variable name"
+		err.Hint = "Did you forget to provide a variable name?"
+		err.Spans = []ErrorSpan{
+			NewMainErrorSpan(span, "missing name"),
+		}
+
+		return true
+	}
+
 	return false
 }

pkg/compiler/internal/diagnostics/match_common_errors.go

@@ -19,5 +19,9 @@ func matchCommonErrors(src *file.Source, err *CompilationError, offending *Token
 		}
 	}
 
+	if isMismatched(err.Message) {
+
+	}
+
 	return false
 }

pkg/compiler/internal/diagnostics/match_for_loop_errors.go

@@ -62,6 +62,48 @@ func matchForLoopErrors(src *file.Source, err *CompilationError, offending *Toke
 				NewMainErrorSpan(span, "missing variable"),
 			}
 
+			return true
+		} else if isNoAlternative(msg) {
+			span := spanFromTokenSafe(offending.Token(), src)
+			span.Start = span.End
+			span.End = span.Start + 1
+
+			err.Message = "Incomplete COLLECT clause"
+			err.Hint = "COLLECT must specify a grouping key, an AGGREGATE clause, or WITH COUNT."
+			err.Spans = []ErrorSpan{
+				NewMainErrorSpan(span, "missing grouping or aggregation"),
+			}
+
+			return true
+		}
+	}
+
+	if is(offending, "INTO") {
+		span := spanFromTokenSafe(offending.Token(), src)
+		span.Start = span.End + 1
+		span.End = span.Start + 1
+
+		err.Message = "Expected variable name after INTO"
+		err.Hint = "Provide a variable name to store grouped values, e.g. INTO groups."
+		err.Spans = []ErrorSpan{
+			NewMainErrorSpan(span, "missing variable name"),
+		}
+
+		return true
+	}
+
+	if is(offending, "AGGREGATE") {
+		if isNoAlternative(err.Message) {
+			span := spanFromTokenSafe(offending.Token(), src)
+			span.Start = span.End + 1
+			span.End = span.Start + 1
+
+			err.Message = "Expected variable assignment after AGGREGATE"
+			err.Hint = "Provide at least one variable assignment, e.g. AGGREGATE total = COUNT(x)."
+			err.Spans = []ErrorSpan{
+				NewMainErrorSpan(span, "missing variable assignment"),
+			}
+
 			return true
 		}
 	}
@@ -71,7 +113,7 @@ func matchForLoopErrors(src *file.Source, err *CompilationError, offending *Toke
 		span.Start = span.End
 		span.End = span.Start + 1
 
-		err.Message = "Expected condition after 'FILTER'"
+		err.Message = "Incomplete FILTER clause"
 		err.Hint = "FILTER requires a boolean expression."
 		err.Spans = []ErrorSpan{
 			NewMainErrorSpan(span, "missing expression"),

pkg/compiler/internal/diagnostics/match_return_value_errors.go

@@ -26,6 +26,8 @@ func matchMissingReturnValue(src *file.Source, err *CompilationError, offending
 	}
 
 	span := spanFromTokenSafe(offending.Token(), src)
+	span.Start = span.End
+	span.End = span.Start + 1
 	err.Message = fmt.Sprintf("Expected expression after '%s'", offending)
 	err.Hint = "Did you forget to provide a value to return?"
 	err.Spans = []ErrorSpan{

pkg/file/helpers.go

@@ -13,3 +13,15 @@ func SkipWhitespaceForward(content string, offset int) int {
 
 	return offset
 }
+
+func SkipHorizontalWhitespaceForward(content string, offset int) int {
+	for offset < len(content) {
+		ch := content[offset]
+		// Skip spaces and tabs only; do NOT cross line breaks
+		if ch != ' ' && ch != '\t' {
+			break
+		}
+		offset++
+	}
+	return offset
+}

pkg/file/snippet.go

@@ -34,7 +34,6 @@ func NewSnippetWithCaret(lines []string, span Span, line int) Snippet {
 	endCol := computeVisualOffset(srcLine, span.End-lineStartOffset+1)
 
 	caret := ""
-
 	if endCol <= startCol+1 {
 		caret = strings.Repeat(" ", startCol) + "^"
 	} else {

pkg/file/source.go

@@ -43,20 +43,36 @@ func (s *Source) LocationAt(span Span) (line, column int) {
 		return 0, 0
 	}
 
-	total := 0
 	offset := span.Start
+	total := 0
 
 	for i, l := range s.lines {
-		lineLen := len(l) + 1 // +1 for newline
+		lineLen := len(l) + 1 // +1 for '\n'
+		lineStart := total
+		lineEndWithNL := total + lineLen
 
-		if total+lineLen > offset {
+		// If offset is exactly at the start of this line (not the very first line),
+		// treat it as the end of the previous line.
+		if offset == lineStart && i > 0 {
+			prev := s.lines[i-1]
+			return i, len(prev) + 1
+		}
+
+		if lineEndWithNL > offset {
+			// Normal case: offset lives on this line
 			return i + 1, offset - total + 1
 		}
 
-		total += lineLen
+		total = lineEndWithNL
 	}
 
-	return total, 1
+	// If we somehow fell through, clamp to last line end
+	if len(s.lines) > 0 {
+		last := s.lines[len(s.lines)-1]
+		return len(s.lines), len(last) + 1
+	}
+
+	return 0, 0
 }
 
 func (s *Source) Snippet(span Span) []Snippet {

test/integration/compiler/compiler_errors_syntax_loop_test.go

@@ -0,0 +1,197 @@
+package compiler_test
+
+import (
+	"testing"
+
+	"github.com/MontFerret/ferret/pkg/compiler"
+)
+
+func TestForLoopSyntaxErrors(t *testing.T) {
+	RunUseCases(t, []UseCase{
+		ErrorCase(
+			`
+			FOR i IN [1, 2, 3]
+				RETURN
+		`, E{
+				Kind:    compiler.SyntaxError,
+				Message: "Expected expression after 'RETURN'",
+				Hint:    "Did you forget to provide a value to return?",
+			}, "Missing return value in for loop"),
+
+		ErrorCase(
+			`
+			FOR i IN 
+				RETURN i
+		`, E{
+				Kind:    compiler.SyntaxError,
+				Message: "Expected expression after 'IN'",
+				Hint:    "Each FOR loop must iterate over a collection or range.",
+			}, "Missing iterable in FOR"),
+
+		ErrorCase(
+			`
+			FOR i [1, 2, 3]
+				RETURN i
+		`, E{
+				Kind:    compiler.SyntaxError,
+				Message: "Expected 'IN' after loop variable",
+				Hint:    "Use 'FOR x IN [iterable]' syntax.",
+			}, "Missing IN in FOR"),
+
+		ErrorCase(
+			`
+			FOR IN [1, 2, 3]
+				RETURN i
+		`, E{
+				Kind:    compiler.SyntaxError,
+				Message: "Expected loop variable before 'IN'",
+				Hint:    "FOR must declare a variable.",
+			}, "FOR without variable"),
+
+		ErrorCase(
+			`
+			LET users = []
+			FOR x IN users
+				FILTER
+				RETURN x
+		`, E{
+				Kind:    compiler.SyntaxError,
+				Message: "Incomplete FILTER clause",
+				Hint:    "FILTER requires a boolean expression.",
+			}, "FILTER with no expression"),
+
+		ErrorCase(
+			`
+			LET users = []
+			FOR x IN users
+				LIMIT
+				RETURN x
+		`, E{
+				Kind:    compiler.SyntaxError,
+				Message: "Expected number after 'LIMIT'",
+				Hint:    "LIMIT requires a numeric value.",
+			}, "LIMIT with no value"),
+
+		ErrorCase(
+			`
+			LET users = []
+			FOR x IN users
+				LIMIT 1, 2, 3
+				RETURN x
+		`, E{
+				Kind:    compiler.SyntaxError,
+				Message: "Too many arguments provided to LIMIT clause",
+				Hint:    "LIMIT accepts at most two arguments: offset and count.",
+			}, "LIMIT with too many values"),
+
+		ErrorCase(
+			`
+			LET users = []
+			FOR x IN users
+				LIMIT 1, 2,
+				RETURN x
+		`, E{
+				Kind:    compiler.SyntaxError,
+				Message: "Too many arguments provided to LIMIT clause",
+				Hint:    "LIMIT accepts at most two arguments: offset and count.",
+			}, "LIMIT unexpected comma"),
+
+		ErrorCase(
+			`
+			LET users = []
+			FOR x IN users
+				LIMIT 1,
+				RETURN x
+		`, E{
+				Kind:    compiler.SyntaxError,
+				Message: "Dangling comma in LIMIT clause",
+				Hint:    "LIMIT accepts one or two arguments. Did you forget to add a value?",
+			}, "LIMIT unexpected comma 2"),
+
+		ErrorCase(
+			`
+			LET users = []
+			FOR x IN users
+				LIMIT ,
+				RETURN x
+		`, E{
+				Kind:    compiler.SyntaxError,
+				Message: "Dangling comma in LIMIT clause",
+				Hint:    "LIMIT accepts one or two arguments. Did you forget to add a value?",
+			}, "LIMIT unexpected comma 3"),
+
+		ErrorCase(
+			`
+			LET users = []
+			FOR x IN users
+				LIMIT,
+				RETURN x
+		`, E{
+				Kind:    compiler.SyntaxError,
+				Message: "Dangling comma in LIMIT clause",
+				Hint:    "LIMIT accepts one or two arguments. Did you forget to add a value?",
+			}, "LIMIT unexpected comma 4"),
+
+		ErrorCase(
+			`
+			LET users = []
+			FOR x IN users
+				COLLECT =
+				RETURN x
+		`, E{
+				Kind:    compiler.SyntaxError,
+				Message: "Expected variable before '=' in COLLECT",
+				Hint:    "COLLECT must group by a variable.",
+			}, "COLLECT with no variable"),
+
+		ErrorCase(
+			`
+			LET users = []
+			FOR x IN users
+				COLLECT
+				RETURN x
+		`, E{
+				Kind:    compiler.SyntaxError,
+				Message: "Incomplete COLLECT clause",
+				Hint:    "COLLECT must specify a grouping key, an AGGREGATE clause, or WITH COUNT.",
+			}, "COLLECT with no variables"),
+
+		ErrorCase(
+			`
+			LET users = []
+			FOR i IN users
+				COLLECT gender = i.gender INTO
+				RETURN {
+					gender,
+					values
+				}`, E{
+				Kind:    compiler.SyntaxError,
+				Message: "Expected variable name after INTO",
+				Hint:    "Provide a variable name to store grouped values, e.g. INTO groups.",
+			}, "COLLECT INTO with no variable"),
+
+		ErrorCase(
+			`
+			LET users = []
+			FOR x IN users
+				COLLECT AGGREGATE total = 
+				RETURN total
+		`, E{
+				Kind:    compiler.SyntaxError,
+				Message: "Expected expression after '=' for variable 'total'",
+				Hint:    "Did you forget to provide a value?",
+			}, "COLLECT AGGREGATE without expression"),
+
+		ErrorCase(
+			`
+			LET users = []
+			FOR x IN users
+				COLLECT AGGREGATE 
+				RETURN total
+		`, E{
+				Kind:    compiler.SyntaxError,
+				Message: "Expected variable assignment after AGGREGATE",
+				Hint:    "Provide at least one variable assignment, e.g. AGGREGATE total = COUNT(x).",
+			}, "COLLECT AGGREGATE without expression 2"),
+	})
+}

test/integration/compiler/compiler_errors_syntax_test.go

@@ -8,6 +8,25 @@ import (
 
 func TestSyntaxErrors(t *testing.T) {
 	RunUseCases(t, []UseCase{
+		ErrorCase(
+			`
+			LET
+		`, E{
+				Kind:    compiler.SyntaxError,
+				Message: "Expected variable name",
+				Hint:    "Did you forget to provide a variable name?",
+			}, "Missing variable name"),
+
+		ErrorCase(
+			`
+			LET
+			RETURN 5
+		`, E{
+				Kind:    compiler.SyntaxError,
+				Message: "Expected variable name",
+				Hint:    "Did you forget to provide a variable name?",
+			}, "Missing variable name 2"),
+
 		ErrorCase(
 			`
 			LET i = NONE
@@ -27,16 +46,6 @@ func TestSyntaxErrors(t *testing.T) {
 				Hint:    "Did you forget to provide a value to return?",
 			}, "Missing return value"),
 
-		ErrorCase(
-			`
-			FOR i IN [1, 2, 3]
-				RETURN
-		`, E{
-				Kind:    compiler.SyntaxError,
-				Message: "Expected expression after 'RETURN'",
-				Hint:    "Did you forget to provide a value to return?",
-			}, "Missing return value in for loop"),
-
 		ErrorCase(
 			`
 			LET i =
@@ -49,138 +58,46 @@ func TestSyntaxErrors(t *testing.T) {
 
 		ErrorCase(
 			`
-			FOR i IN 
-				RETURN i
+			LET i =
+			LET j = 5
+			RETURN i
 		`, E{
 				Kind:    compiler.SyntaxError,
-				Message: "Expected expression after 'IN'",
-				Hint:    "Each FOR loop must iterate over a collection or range.",
-			}, "Missing iterable in FOR"),
-
-		ErrorCase(
-			`
-			FOR i [1, 2, 3]
-				RETURN i
-		`, E{
-				Kind:    compiler.SyntaxError,
-				Message: "Expected 'IN' after loop variable",
-				Hint:    "Use 'FOR x IN [iterable]' syntax.",
-			}, "Missing IN in FOR"),
-
-		ErrorCase(
-			`
-			FOR IN [1, 2, 3]
-				RETURN i
-		`, E{
-				Kind:    compiler.SyntaxError,
-				Message: "Expected loop variable before 'IN'",
-				Hint:    "FOR must declare a variable.",
-			}, "FOR without variable"),
-
-		ErrorCase(
-			`
-			LET users = []
-			FOR x IN users
-				COLLECT =
-				RETURN x
-		`, E{
-				Kind:    compiler.SyntaxError,
-				Message: "Expected variable before '=' in COLLECT",
-				Hint:    "COLLECT must group by a variable.",
-			}, "COLLECT with no variable"),
-
-		ErrorCase(
-			`
-			LET users = []
-			FOR x IN users
-				COLLECT AGGREGATE total = 
-				RETURN total
-		`, E{
-				Kind:    compiler.SyntaxError,
-				Message: "Expected expression after '=' for variable 'total'",
+				Message: "Expected expression after '=' for variable 'i'",
 				Hint:    "Did you forget to provide a value?",
-			}, "COLLECT AGGREGATE without expression"),
+			}, "Missing variable assignment value 2"),
 
 		ErrorCase(
 			`
-			LET users = []
-			FOR x IN users
-				FILTER
-				RETURN x
+			LET i =
+			FOR j IN [1, 2, 3] RETURN j
 		`, E{
 				Kind:    compiler.SyntaxError,
-				Message: "Expected condition after 'FILTER'",
-				Hint:    "FILTER requires a boolean expression.",
-			}, "FILTER with no expression"),
+				Message: "Expected expression after '=' for variable 'i'",
+				Hint:    "Did you forget to provide a value?",
+			}, "Missing variable assignment value 3"),
 
-		ErrorCase(
+		SkipErrorCase(
 			`
-			LET users = []
-			FOR x IN users
-				LIMIT
-				RETURN x
+			LET o = { foo: "bar" }
+			LET i = o.
+			RETURN i
 		`, E{
 				Kind:    compiler.SyntaxError,
-				Message: "Expected number after 'LIMIT'",
-				Hint:    "LIMIT requires a numeric value.",
-			}, "LIMIT with no value"),
+				Message: "Expected expression after '=' for variable 'i'",
+				Hint:    "Did you forget to provide a value?",
+			}, "Incomplete member access"),
 
-		ErrorCase(
+		SkipErrorCase(
 			`
-			LET users = []
-			FOR x IN users
-				LIMIT 1, 2, 3
-				RETURN x
+			LET o = { foo: "bar" }
+			LET i = o.
+			FUNC(i)
+			RETURN i
 		`, E{
 				Kind:    compiler.SyntaxError,
-				Message: "Too many arguments provided to LIMIT clause",
-				Hint:    "LIMIT accepts at most two arguments: offset and count.",
-			}, "LIMIT with too many values"),
-
-		ErrorCase(
-			`
-			LET users = []
-			FOR x IN users
-				LIMIT 1, 2,
-				RETURN x
-		`, E{
-				Kind:    compiler.SyntaxError,
-				Message: "Too many arguments provided to LIMIT clause",
-				Hint:    "LIMIT accepts at most two arguments: offset and count.",
-			}, "LIMIT unexpected comma"),
-
-		ErrorCase(
-			`
-			LET users = []
-			FOR x IN users
-				LIMIT 1,
-				RETURN x
-		`, E{
-				Kind:    compiler.SyntaxError,
-				Message: "Dangling comma in LIMIT clause",
-				Hint:    "LIMIT accepts one or two arguments. Did you forget to add a value?",
-			}, "LIMIT unexpected comma 2"),
-		ErrorCase(
-			`
-			LET users = []
-			FOR x IN users
-				LIMIT ,
-				RETURN x
-		`, E{
-				Kind:    compiler.SyntaxError,
-				Message: "Dangling comma in LIMIT clause",
-				Hint:    "LIMIT accepts one or two arguments. Did you forget to add a value?",
-			}, "LIMIT unexpected comma 3"),
-		ErrorCase(
-			`
-			LET users = []
-			FOR x IN users
-				LIMIT,
-				RETURN x
-		`, E{
-				Kind:    compiler.SyntaxError,
-				Message: "Dangling comma in LIMIT clause",
-				Hint:    "LIMIT accepts one or two arguments. Did you forget to add a value?",
-			}, "LIMIT unexpected comma 4"),
+				Message: "Expected expression after '=' for variable 'i'",
+				Hint:    "Did you forget to provide a value?",
+			}, "Incomplete member access 2"),
 	})
 }