decoder: Introduce helper functions for completion inside ObjectConsExpr

decoder/expression.go

@@ -2,6 +2,7 @@ package decoder
 
 import (
 	"context"
+	"unicode/utf8"
 
 	"github.com/hashicorp/hcl-lang/lang"
 	"github.com/hashicorp/hcl-lang/reference"
@@ -167,3 +168,39 @@ func newEmptyExpressionAtPos(filename string, pos hcl.Pos) hcl.Expression {
 		},
 	}
 }
+
+// recoverLeftBytes seeks left from given pos in given slice of bytes
+// and recovers all bytes up until f matches, including that match.
+// This allows recovery of incomplete configuration which is not
+// present in the parsed AST during completion.
+//
+// Zero bytes is returned if no match was found.
+func recoverLeftBytes(b []byte, pos hcl.Pos, f func(byteOffset int, r rune) bool) []byte {
+	firstRune, size := utf8.DecodeLastRune(b[:pos.Byte])
+	offset := pos.Byte - size
+
+	// check for early match
+	if f(pos.Byte, firstRune) {
+		return b[offset:pos.Byte]
+	}
+
+	for offset > 0 {
+		nextRune, size := utf8.DecodeLastRune(b[:offset])
+		if f(offset, nextRune) {
+			// record the matched offset
+			// and include the matched last rune
+			startByte := offset - size
+			return b[startByte:pos.Byte]
+		}
+		offset -= size
+	}
+
+	return []byte{}
+}
+
+// isObjectItemTerminatingRune returns true if the given rune
+// is considered a left terminating character for an item
+// in hclsyntax.ObjectConsExpr.
+func isObjectItemTerminatingRune(r rune) bool {
+	return r == '\n' || r == ',' || r == '{'
+}

decoder/expression_test.go

@@ -1,5 +1,14 @@
 package decoder
 
+import (
+	"bytes"
+	"fmt"
+	"testing"
+	"unicode"
+
+	"github.com/hashicorp/hcl/v2"
+)
+
 var (
 	_ Expression = Any{}
 	_ Expression = Keyword{}
@@ -33,3 +42,57 @@ var (
 	_ ReferenceTargetsExpression = Reference{}
 	_ ReferenceTargetsExpression = Tuple{}
 )
+
+func TestRecoverLeftBytes(t *testing.T) {
+	testCases := []struct {
+		b             []byte
+		pos           hcl.Pos
+		f             func(int, rune) bool
+		expectedBytes []byte
+	}{
+		{
+			[]byte(`toot  foobar`),
+			hcl.Pos{Line: 1, Column: 13, Byte: 12},
+			func(i int, r rune) bool {
+				return unicode.IsSpace(r)
+			},
+			[]byte(` foobar`),
+		},
+		{
+			[]byte(`hello👋world and other planets`),
+			hcl.Pos{Line: 1, Column: 15, Byte: 14},
+			func(i int, r rune) bool {
+				return r == '👋'
+			},
+			[]byte(`👋world`),
+		},
+		{
+			[]byte(`hello world👋and other planets`),
+			hcl.Pos{Line: 1, Column: 16, Byte: 15},
+			func(i int, r rune) bool {
+				return r == '👋'
+			},
+			[]byte(`👋`),
+		},
+		{
+			[]byte(`attr = {
+  foo = "foo",
+  bar = 
+}
+`),
+			hcl.Pos{Line: 3, Column: 9, Byte: 32},
+			func(i int, r rune) bool {
+				return r == '\n' || r == ','
+			},
+			[]byte("\n  bar = "),
+		},
+	}
+	for i, tc := range testCases {
+		t.Run(fmt.Sprintf("%d", i), func(t *testing.T) {
+			recoveredBytes := recoverLeftBytes(tc.b, tc.pos, tc.f)
+			if !bytes.Equal(tc.expectedBytes, recoveredBytes) {
+				t.Fatalf("mismatch!\nexpected:  %q\nrecovered: %q\n", string(tc.expectedBytes), string(recoveredBytes))
+			}
+		})
+	}
+}