behavior and cases: more test coverage for old issues

Closes ziglang#2622
Closes ziglang#2727
Closes ziglang#6047
Closes ziglang#6947

Author: wooster0

test/behavior.zig

@@ -43,7 +43,9 @@ test {
     _ = @import("behavior/bugs/2346.zig");
     _ = @import("behavior/bugs/2557.zig");
     _ = @import("behavior/bugs/2578.zig");
+    _ = @import("behavior/bugs/2622.zig");
     _ = @import("behavior/bugs/2692.zig");
+    _ = @import("behavior/bugs/2727.zig");
     _ = @import("behavior/bugs/2889.zig");
     _ = @import("behavior/bugs/3007.zig");
     _ = @import("behavior/bugs/3046.zig");
@@ -62,10 +64,12 @@ test {
     _ = @import("behavior/bugs/5413.zig");
     _ = @import("behavior/bugs/5474.zig");
     _ = @import("behavior/bugs/5487.zig");
+    _ = @import("behavior/bugs/6047.zig");
     _ = @import("behavior/bugs/6456.zig");
     _ = @import("behavior/bugs/6781.zig");
     _ = @import("behavior/bugs/6850.zig");
     _ = @import("behavior/bugs/6905.zig");
+    _ = @import("behavior/bugs/6947.zig");
     _ = @import("behavior/bugs/7003.zig");
     _ = @import("behavior/bugs/7047.zig");
     _ = @import("behavior/bugs/7187.zig");

test/behavior/bugs/2622.zig

@@ -0,0 +1,8 @@
+var buf: []u8 = undefined;
+
+test "reslice of undefined global var slice" {
+    var mem: [100]u8 = [_]u8{0} ** 100;
+    buf = &mem;
+    const x = buf[0..1];
+    try @import("std").testing.expect(x.len == 1 and x[0] == 0);
+}

test/behavior/bugs/2727.zig

@@ -0,0 +1,10 @@
+fn t() bool {
+    return true;
+}
+
+test {
+    comptime var i: usize = 0;
+    inline while (i < 2) : (i += 1) {
+        if (t()) {} else return;
+    }
+}

test/behavior/bugs/6047.zig

@@ -0,0 +1,12 @@
+fn getError() !void {
+    return error.Test;
+}
+
+fn getError2() !void {
+    var a: u8 = 'c';
+    try if (a == 'a') getError() else if (a == 'b') getError() else getError();
+}
+
+test "`try`ing an if/else expression" {
+    try @import("std").testing.expectError(error.Test, getError2());
+}

test/behavior/bugs/6947.zig

@@ -0,0 +1,8 @@
+fn destroy(ptr: *void) void {
+    _ = ptr;
+}
+
+test {
+    var slice: []void = undefined;
+    destroy(&slice[0]);
+}

test/cases/compile_errors/comptime_struct_field_assignment.zig

@@ -0,0 +1,23 @@
+const std = @import("std");
+const testing = std.testing;
+
+const State = struct {
+    comptime id: bool = true,
+
+    pub fn init(comptime id: bool) State {
+        return State{ .id = id };
+    }
+};
+
+test "test states" {
+    const s1 = State.init(true);
+    try testing.expect(s1.id == true);
+
+    _ = State.init(false);
+}
+
+// error
+// backend=stage2
+// target=native
+//
+// :8:29: error: value stored in comptime field does not match the default value of the field