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, 15 insertions, 19 deletions

diff --git a/src/Compilation.zig b/src/Compilation.zig
index a34d0cd198..00cdba85a4 100644
--- a/src/Compilation.zig
+++ b/src/Compilation.zig
@@ -1709,7 +1709,9 @@ pub fn update(self: *Compilation) !void {
         // in the start code, but when using the stage1 backend that won't happen,
         // so in order to run AstGen on the root source file we put it into the
         // import_table here.
-        if (use_stage1) {
+        // Likewise, in the case of `zig test`, the test runner is the root source file,
+        // and so there is nothing to import the main file.
+        if (use_stage1 or self.bin_file.options.is_test) {
             _ = try module.importPkg(module.main_pkg);
         }
 
@@ -1725,6 +1727,9 @@ pub fn update(self: *Compilation) !void {
 
         if (!use_stage1) {
             try self.work_queue.writeItem(.{ .analyze_pkg = std_pkg });
+            if (self.bin_file.options.is_test) {
+                try self.work_queue.writeItem(.{ .analyze_pkg = module.main_pkg });
+            }
         }
     }
 
@@ -2053,24 +2058,7 @@ pub fn performAllTheWork(self: *Compilation) error{ TimerUnsupported, OutOfMemor
                 assert(decl.has_tv);
                 assert(decl.ty.hasCodeGenBits());
 
-                self.bin_file.updateDecl(module, decl) catch |err| switch (err) {
-                    error.OutOfMemory => return error.OutOfMemory,
-                    error.AnalysisFail => {
-                        decl.analysis = .codegen_failure;
-                        continue;
-                    },
-                    else => {
-                        try module.failed_decls.ensureUnusedCapacity(gpa, 1);
-                        module.failed_decls.putAssumeCapacityNoClobber(decl, try Module.ErrorMsg.create(
-                            gpa,
-                            decl.srcLoc(),
-                            "unable to codegen: {s}",
-                            .{@errorName(err)},
-                        ));
-                        decl.analysis = .codegen_failure_retryable;
-                        continue;
-                    },
-                };
+                try module.linkerUpdateDecl(decl);
             },
         },
         .codegen_func => |func| switch (func.owner_decl.analysis) {
@@ -2396,6 +2384,14 @@ pub fn performAllTheWork(self: *Compilation) error{ TimerUnsupported, OutOfMemor
             };
         },
     };
+
+    if (self.bin_file.options.is_test and self.totalErrorCount() == 0) {
+        // The `test_functions` decl has been intentionally postponed until now,
+        // at which point we must populate it with the list of test functions that
+        // have been discovered and not filtered out.
+        const mod = self.bin_file.options.module.?;
+        try mod.populateTestFunctions();
+    }
 }
 
 const AstGenSrc = union(enum) {