stage2: `zig test` now works with the LLVM backend

Frontend improvements:

 * When compiling in `zig test` mode, put a task on the work queue to
   analyze the main package root file. Normally, start code does
   `_ = import("root");` to make Zig analyze the user's code, however in
   the case of `zig test`, the root source file is the test runner.
   Without this change, no tests are picked up.
 * In the main pipeline, once semantic analysis is finished, if there
   are no compile errors, populate the `test_functions` Decl with the
   set of test functions picked up from semantic analysis.
 * Value: add `array` and `slice` Tags.

LLVM backend improvements:

 * Fix incremental updates of globals. Previously the
   value of a global would not get replaced with a new value.
 * Fix LLVM type of arrays. They were incorrectly sending
   the ABI size as the element count.
 * Remove the FuncGen parameter from genTypedValue. This function is for
   generating global constants and there is no function available when
   it is being called.
   - The `ref_val` case is now commented out. I'd like to eliminate
     `ref_val` as one of the possible Value Tags. Instead it should
     always be done via `decl_ref`.
 * Implement constant value generation for slices, arrays, and structs.
 * Constant value generation for functions supports the `decl_ref` tag.

1 files changed, 22 insertions, 0 deletions

diff --git a/src/type.zig b/src/type.zig
index 731c69b806..4dd1a15fdd 100644
--- a/src/type.zig
+++ b/src/type.zig
@@ -1526,6 +1526,8 @@ pub const Type = extern union {
             .var_args_param => unreachable,
 
             .@"struct" => {
+                const s = self.castTag(.@"struct").?.data;
+                assert(s.status == .have_layout);
                 @panic("TODO abiSize struct");
             },
             .enum_simple, .enum_full, .enum_nonexhaustive => {
@@ -2768,6 +2770,26 @@ pub const Type = extern union {
         }
     }
 
+    pub fn structFieldCount(ty: Type) usize {
+        switch (ty.tag()) {
+            .@"struct" => {
+                const struct_obj = ty.castTag(.@"struct").?.data;
+                return struct_obj.fields.count();
+            },
+            else => unreachable,
+        }
+    }
+
+    pub fn structFieldType(ty: Type, index: usize) Type {
+        switch (ty.tag()) {
+            .@"struct" => {
+                const struct_obj = ty.castTag(.@"struct").?.data;
+                return struct_obj.fields.values()[index].ty;
+            },
+            else => unreachable,
+        }
+    }
+
     pub fn declSrcLoc(ty: Type) Module.SrcLoc {
         switch (ty.tag()) {
             .enum_full, .enum_nonexhaustive => {