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AnnaShaleva merged 1 commit into from
Jan 23, 2026
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compiler: Fix expression switch with non-last default #4078

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8 changes: 8 additions & 0 deletions pkg/compiler/codegen.go
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Original file line number Diff line number Diff line change
Expand Up @@ -878,6 +878,14 @@ func (c *codegen) Visit(node ast.Node) ast.Visitor {
c.currentSwitch = label
c.pushStackLabel(label, 1)

last := len(n.Body.List) - 1
for i := range last {
if n.Body.List[i].(*ast.CaseClause).List == nil { // early default
n.Body.List[i], n.Body.List[last] = n.Body.List[last], n.Body.List[i]
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@AnnaShaleva AnnaShaleva Dec 3, 2025

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We need to check if this substitution affects generated debug info. Lines info stored in debug info for substituted default should match the source code.

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@cthulhu-rider cthulhu-rider Dec 3, 2025

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how can i check this?

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@AnnaShaleva AnnaShaleva Dec 4, 2025

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See how saveSequencePoint works, ensure that proper statement boundaries will be stored in the debug info file on compilation:

neo-go/pkg/compiler/debug.go

Line 128 in 93fe450

func (c *codegen) saveSequencePoint(n ast.Node) {

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@AnnaShaleva AnnaShaleva Dec 11, 2025

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@cthulhu-rider ping.

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@cthulhu-rider cthulhu-rider Jan 20, 2026

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func TestSwitch(t *testing.T) {
	_, di, err := compiler.CompileWithOptions("contract.go", strings.NewReader(`
package contract

func F() int {
  switch {
  case true:
    return 1
  default:
    return 0
  }
}
`), nil)
	require.NoError(t, err)

	for _, m := range di.Methods {
		for _, p := range m.SeqPoints {
			j, err := json.MarshalIndent(p, "", " ")
			require.NoError(t, err)
			fmt.Println(string(j))
		}
	}
}

w/ default going after case (more usual):

{
 "Opcode": 8,
 "Document": 0,
 "StartLine": 7,
 "StartCol": 5,
 "EndLine": 7,
 "EndCol": 13
}
{
 "Opcode": 13,
 "Document": 0,
 "StartLine": 9,
 "StartCol": 5,
 "EndLine": 9,
 "EndCol": 13
}
{
 "Opcode": 15,
 "Document": 0,
 "StartLine": 4,
 "StartCol": 14,
 "EndLine": 11,
 "EndCol": 2
}

and before:

{
 "Opcode": 8,
 "Document": 0,
 "StartLine": 9,
 "StartCol": 5,
 "EndLine": 9,
 "EndCol": 13
}
{
 "Opcode": 13,
 "Document": 0,
 "StartLine": 7,
 "StartCol": 5,
 "EndLine": 7,
 "EndCol": 13
}
{
 "Opcode": 15,
 "Document": 0,
 "StartLine": 4,
 "StartCol": 14,
 "EndLine": 11,
 "EndCol": 2
}

anything that needs to be fixed?

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@AnnaShaleva AnnaShaleva Jan 23, 2026

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So far, the following program gives as 3 sequence points with RET opcodes, every opcode matches return line:

			f, di, err := CompileWithOptions("contract.go", strings.NewReader(` // 1
			package contract			// 2
										// 3
			func F(b bool) int {		// 4	18: RET (lines 4-11)
			  switch b {				// 5
			  case true:				// 6
			    return 1				// 7	11: RET	(line 7)
			  default:					// 8
			    return 0				// 9	16: RET	(line 9)
			  }							// 10
			}							// 11
		`), nil)
			require.NoError(t, err)

The bytecode is:

NEO-GO-VM 0 > loadbase64 VwABeEoIlyYHRRFAIgVFEEBFQA==
READY: loaded 19 instructions
NEO-GO-VM 0 > ops
INDEX    OPCODE      PARAMETER
0        INITSLOT    0 local, 1 arg    <<
3        LDARG0
4        DUP
5        PUSHT
6        EQUAL
7        JMPIFNOT    14 (7/07)
9        DROP
10       PUSH1
11       RET
12       JMP         17 (5/05)
14       DROP
15       PUSH0
16       RET
17       DROP
18       RET

The updated version of the program with default going before case gives the following sequence points:

			f, di, err := CompileWithOptions("contract.go", strings.NewReader(` // 1
			package contract			// 2
										// 3
			func F(b bool) int {		// 4	18: RET (lines 4-11)
			  switch b {				// 5
			  default:					// 6
			    return 0				// 7	16: RET	(line 7)
			  case true:				// 8
			    return 1				// 9	11: RET	(line 9)
			  }							// 10
			}							// 11
		`), nil)
			require.NoError(t, err)

The generated bytecode is not changed (as expected).

From the last output we see that 11: RET bounds match exactly the return 1 case, so everything works as expected.

break
}
}

startLabels := make([]uint16, len(n.Body.List))
for i := range startLabels {
startLabels[i] = c.newLabel()
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40 changes: 40 additions & 0 deletions pkg/compiler/switch_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -122,6 +122,46 @@ var switchTestCases = []testCase{
`,
big.NewInt(1),
},
{
"case after first default",
`func F%d() int {
a := 5
switch a {
default: return 4
case 5: return 2
}
}
`,
big.NewInt(2),
},
{
"case after intermediate default",
`func F%d() int {
a := 6
switch a {
case 5: return 2
default: return 4
case 6:
}
return 1
}
`,
big.NewInt(1),
},
{
"intermediate default",
`func F%d() int {
a := 3
switch a {
case 5: return 2
default: return 4
case 6:
}
return 1
}
`,
big.NewInt(4),
},
{
"expression in case clause",
`func F%d() int {
Expand Down
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