proc: allow breakpoint conditions to contain a single boolean variable

Fixes a bug where breakpoint condition evaluation would never load the
value if the breakpoint condition consisted of just a single variable.

Fix #1264

_fixtures/issue1264.go

@@ -0,0 +1,10 @@
+package main
+
+import "fmt"
+
+func main() {
+	for i := 0; i < 4; i++ {
+		equalsTwo := i == 2
+		fmt.Printf("i: %d -> equalsTwo: %t \n", i, equalsTwo) // :8
+	}
+}

pkg/proc/breakpoints.go

@@ -181,12 +181,13 @@ func evalBreakpointCondition(thread Thread, cond ast.Expr) (bool, error) {
 	if err != nil {
 		return true, fmt.Errorf("error evaluating expression: %v", err)
 	}
-	if v.Unreadable != nil {
-		return true, fmt.Errorf("condition expression unreadable: %v", v.Unreadable)
-	}
 	if v.Kind != reflect.Bool {
 		return true, errors.New("condition expression not boolean")
 	}
+	v.loadValue(loadFullValue)
+	if v.Unreadable != nil {
+		return true, fmt.Errorf("condition expression unreadable: %v", v.Unreadable)
+	}
 	return constant.BoolVal(v.Value), nil
 }
 

pkg/proc/proc_test.go

@@ -3862,3 +3862,14 @@ func TestOptimizationCheck(t *testing.T) {
 		})
 	}
 }
+
+func TestIssue1264(t *testing.T) {
+	// It should be possible to set a breakpoint condition that consists only
+	// of evaluating a single boolean variable.
+	withTestProcess("issue1264", t, func(p proc.Process, fixture protest.Fixture) {
+		bp := setFileBreakpoint(p, t, fixture, 8)
+		bp.Cond = &ast.Ident{Name: "equalsTwo"}
+		assertNoError(proc.Continue(p), t, "Continue()")
+		assertLineNumber(p, t, 8, "after continue")
+	})
+}