From 1f2bd5d4d22797071a344647191e63c7d2fa6f67 Mon Sep 17 00:00:00 2001
From: NeilBrown <neil@brown.name>
Date: Sun, 12 Dec 2021 10:33:39 +1100
Subject: [PATCH] oceani: factor out field reference into per-type handler

knowledge about how field references for strutures is now in
structure-specific code.  This will allow other types to
behave differently.

Signed-off-by: NeilBrown <neil@brown.name>
---
 csrc/oceani-tests.mdc |  4 +--
 csrc/oceani.mdc       | 70 ++++++++++++++++++++++++++-----------------
 2 files changed, 44 insertions(+), 30 deletions(-)

diff --git a/csrc/oceani-tests.mdc b/csrc/oceani-tests.mdc
index 12116d4..d672cff 100644
--- a/csrc/oceani-tests.mdc
+++ b/csrc/oceani-tests.mdc
@@ -973,9 +973,9 @@ various places that `type_err()` are called.
 	.tmp.code:29:12: error: have number but need string
 	.tmp.code:7:8: info: variable 'c' was set as string here.
 	.tmp.code:32:8: error: variable used but not declared: foo
-	.tmp.code:32:8: error: field reference attempted on none, not a struct
+	.tmp.code:32:8: error: field reference on none is not supported
 	.tmp.code:32:16: error: expected none found number
-	.tmp.code:33:14: error: field reference attempted on string, not a struct
+	.tmp.code:33:14: error: field reference on string is not supported
 	.tmp.code:34:14: error: cannot find requested field in foo
 	.tmp.code:35:17: error: have string but need number
 	.tmp.code:38:29: error: expected number (labels not permitted) found Boolean
diff --git a/csrc/oceani.mdc b/csrc/oceani.mdc
index 178532c..e1a2cb0 100644
--- a/csrc/oceani.mdc
+++ b/csrc/oceani.mdc
@@ -110,6 +110,7 @@ structures can be used.
 	## macros
 	struct parse_context;
 	## ast
+	## ast late
 	struct parse_context {
 		struct token_config config;
 		char *file_name;
@@ -789,6 +790,7 @@ which might be reported in error messages.
 		};
 	};
 
+###### ast late
 	struct type {
 		struct text name;
 		struct type *next;
@@ -2620,6 +2622,8 @@ function will be needed.
 
 ###### type functions
 	void (*print_type_decl)(struct type *type, FILE *f);
+	struct type *(*fieldref)(struct type *t, struct parse_context *c,
+				 struct fieldref *f, struct value **vp);
 
 ###### value functions
 
@@ -2724,12 +2728,41 @@ function will be needed.
 		return 1;
 	}
 
+	static int find_struct_index(struct type *type, struct text field)
+	{
+		int i;
+		for (i = 0; i < type->structure.nfields; i++)
+			if (text_cmp(type->structure.fields[i].name, field) == 0)
+				return i;
+		return IndexInvalid;
+	}
+
+	static struct type *structure_fieldref(struct type *t, struct parse_context *c,
+					       struct fieldref *f, struct value **vp)
+	{
+		if (f->index == IndexUnknown) {
+			f->index = find_struct_index(t, f->name);
+			if (f->index < 0)
+				type_err(c, "error: cannot find requested field in %1",
+				         f->left, t, 0, NULL);
+		}
+		if (f->index < 0)
+			return NULL;
+		if (vp) {
+			struct value *v = *vp;
+			v = (void*)v->ptr + t->structure.fields[f->index].offset;
+			*vp = v;
+		}
+		return t->structure.fields[f->index].type;
+	}
+
 	static struct type structure_prototype = {
 		.init = structure_init,
 		.free = structure_free,
 		.free_type = structure_free_type,
 		.print_type_decl = structure_print_type,
 		.prepare_type = structure_prepare_type,
+		.fieldref = structure_fieldref,
 	};
 
 ###### exec type
@@ -2773,16 +2806,6 @@ function will be needed.
 		break;
 	}
 
-###### ast functions
-	static int find_struct_index(struct type *type, struct text field)
-	{
-		int i;
-		for (i = 0; i < type->structure.nfields; i++)
-			if (text_cmp(type->structure.fields[i].name, field) == 0)
-				return i;
-		return IndexInvalid;
-	}
-
 ###### propagate exec cases
 
 	case Xfieldref:
@@ -2790,24 +2813,15 @@ function will be needed.
 		struct fieldref *f = cast(fieldref, prog);
 		struct type *st = propagate_types(f->left, c, perr, NULL, 0);
 
-		if (!st)
-			type_err(c, "error: unknown type for field access", f->left,	// UNTESTED
-			         NULL, 0, NULL);
-		else if (st->init != structure_init)
-			type_err(c, "error: field reference attempted on %1, not a struct",
+		if (!st || !st->fieldref)
+			type_err(c, "error: field reference on %1 is not supported",
 			         f->left, st, 0, NULL);
-		else if (f->index == IndexUnknown) {
-			f->index = find_struct_index(st, f->name);
-			if (f->index < 0)
-				type_err(c, "error: cannot find requested field in %1",
-				         f->left, st, 0, NULL);
-		}
-		if (f->index >= 0) {
-			struct type *ft = st->structure.fields[f->index].type;
-			if (!type_compat(type, ft, rules))
+		else {
+			t = st->fieldref(st, c, f, NULL);
+			if (t && !type_compat(type, t, rules))
 				type_err(c, "error: have %1 but need %2", prog,
-				         ft, rules, type);
-			return ft;
+				         t, rules, type);
+			return t;
 		}
 		break;
 	}
@@ -2818,8 +2832,8 @@ function will be needed.
 		struct fieldref *f = cast(fieldref, e);
 		struct type *ltype;
 		struct value *lleft = linterp_exec(c, f->left, &ltype);
-		lrv = (void*)lleft->ptr + ltype->structure.fields[f->index].offset;
-		rvtype = ltype->structure.fields[f->index].type;
+		lrv = lleft;
+		rvtype = ltype->fieldref(ltype, c, f, &lrv);
 		break;
 	}
 
-- 
2.43.0