Prevent analysis of functions only referenced at comptime

The idea here is that there are two ways we can reference a function at runtime:

* Through a direct call, i.e. where the function is comptime-known
* Through a function pointer

This means we can easily perform a form of rudimentary escape analysis
on functions. If we ever see a `decl_ref` or `ref` of a function, we
have a function pointer, which could "leak" into runtime code, so we
emit the function; but for a plain `decl_val`, there's no need to.

This change means that `comptime { _ = f; }` no longer forces a function
to be emitted, which was used for some things (mainly tests). These use
sites have been replaced with `_ = &f;`, which still triggers analysis
of the function body, since you're taking a pointer to the function.

Resolves: #6256
Resolves: #15353

1 files changed, 7 insertions, 0 deletions

diff --git a/src/Compilation.zig b/src/Compilation.zig
index cc2e2a916b..956948dd86 100644
--- a/src/Compilation.zig
+++ b/src/Compilation.zig
@@ -3193,6 +3193,13 @@ fn processOneJob(comp: *Compilation, job: Job, prog_node: *std.Progress.Node) !v
                 error.OutOfMemory => return error.OutOfMemory,
                 error.AnalysisFail => return,
             };
+            const decl = module.declPtr(decl_index);
+            if (decl.kind == .@"test" and comp.bin_file.options.is_test) {
+                // Tests are always emitted in test binaries. The decl_refs are created by
+                // Module.populateTestFunctions, but this will not queue body analysis, so do
+                // that now.
+                try module.ensureFuncBodyAnalysisQueued(decl.val.castTag(.function).?.data);
+            }
         },
         .update_embed_file => |embed_file| {
             const named_frame = tracy.namedFrame("update_embed_file");