InternPool: fix coerced func hash/eql same as uncoerced

Since the same Key.Func data structure is used for coerced function
bodies as well as uncoerced function bodies, there is danger of them
being hashed and equality-checked as the same. When that happens, the
type of a function body value might be wrong, causing lots of problems.
In this instance, it causes an assertion failure.

This commit fixes it by introducing an `uncoerced_ty` field which
is different than `ty` in the case of `func_coerced` and is used to
differentiate when doing hashing and equality checking.

I have a new behavior test to cover this bug, but it revealed *another*
bug at the same time, so I will fix it in the next commit and and add
the new test therein.

1 files changed, 21 insertions, 2 deletions

diff --git a/src/InternPool.zig b/src/InternPool.zig
index b8eaafceab..0e9e1d4559 100644
--- a/src/InternPool.zig
+++ b/src/InternPool.zig
@@ -594,6 +594,13 @@ pub const Key = union(enum) {
         /// In the case of a generic function, this type will potentially have fewer parameters
         /// than the generic owner's type, because the comptime parameters will be deleted.
         ty: Index,
+        /// If this is a function body that has been coerced to a different type, for example
+        /// ```
+        /// fn f2() !void {}
+        /// const f: fn()anyerror!void = f2;
+        /// ```
+        /// then it contains the original type of the function body.
+        uncoerced_ty: Index,
         /// Index into extra array of the `FuncAnalysis` corresponding to this function.
         /// Used for mutating that data.
         analysis_extra_index: u32,
@@ -990,11 +997,15 @@ pub const Key = union(enum) {
                 // otherwise we would get false negatives for interning generic
                 // function instances which have inferred error sets.
 
-                if (func.generic_owner == .none and func.resolved_error_set_extra_index == 0)
-                    return Hash.hash(seed, asBytes(&func.owner_decl) ++ asBytes(&func.ty));
+                if (func.generic_owner == .none and func.resolved_error_set_extra_index == 0) {
+                    const bytes = asBytes(&func.owner_decl) ++ asBytes(&func.ty) ++
+                        [1]u8{@intFromBool(func.uncoerced_ty == func.ty)};
+                    return Hash.hash(seed, bytes);
+                }
 
                 var hasher = Hash.init(seed);
                 std.hash.autoHash(&hasher, func.generic_owner);
+                std.hash.autoHash(&hasher, func.uncoerced_ty == func.ty);
                 for (func.comptime_args.get(ip)) |arg| std.hash.autoHash(&hasher, arg);
                 if (func.resolved_error_set_extra_index == 0) {
                     std.hash.autoHash(&hasher, func.ty);
@@ -1122,6 +1133,12 @@ pub const Key = union(enum) {
                     )) return false;
                 }
 
+                if ((a_info.ty == a_info.uncoerced_ty) !=
+                    (b_info.ty == b_info.uncoerced_ty))
+                {
+                    return false;
+                }
+
                 if (a_info.ty == b_info.ty)
                     return true;
 
@@ -3371,6 +3388,7 @@ fn extraFuncDecl(ip: *const InternPool, extra_index: u32) Key.Func {
     const func_decl = ip.extraDataTrail(P, extra_index);
     return .{
         .ty = func_decl.data.ty,
+        .uncoerced_ty = func_decl.data.ty,
         .analysis_extra_index = extra_index + std.meta.fieldIndex(P, "analysis").?,
         .zir_body_inst_extra_index = extra_index + std.meta.fieldIndex(P, "zir_body_inst").?,
         .resolved_error_set_extra_index = if (func_decl.data.analysis.inferred_error_set) func_decl.end else 0,
@@ -3392,6 +3410,7 @@ fn extraFuncInstance(ip: *const InternPool, extra_index: u32) Key.Func {
     const func_decl = ip.funcDeclInfo(fi.data.generic_owner);
     return .{
         .ty = fi.data.ty,
+        .uncoerced_ty = fi.data.ty,
         .analysis_extra_index = extra_index + std.meta.fieldIndex(P, "analysis").?,
         .zir_body_inst_extra_index = func_decl.zir_body_inst_extra_index,
         .resolved_error_set_extra_index = if (fi.data.analysis.inferred_error_set) fi.end else 0,