Fixes and optimizations to compiler (browserengineering#226)

* Fix import of constants

* Optimize text metrics call in rt.js

* Fix tests for new constants import code

Author: pavpanchekha

infra/compile.py

@@ -533,15 +533,16 @@ def compile_expr(tree, ctx):
     elif isinstance(tree, ast.Tuple) or isinstance(tree, ast.List):
         return "[" + ", ".join([compile_expr(a, ctx) for a in tree.elts]) + "]"
     elif isinstance(tree, ast.Name):
-        assert tree.id == "self" or tree.id in ctx or tree.id in LAB_IMPORT_CLASSES, f"Could not find variable {tree.id}"
         if tree.id == "self":
             return "this"
         elif tree.id in RT_IMPORTS or tree.id in LAB_IMPORT_CLASSES:
             return tree.id
-        elif ctx.is_global_constant(tree.id):
+        elif ctx.is_global_constant(tree.id) or tree.id in LAB_IMPORT_CONSTANTS:
             return "constants.{}".format(tree.id)
-        else:
+        elif tree.id in ctx:
             return tree.id
+        else:
+            raise AssertionError(f"Could not find variable {tree.id}")
     elif isinstance(tree, ast.Constant):
         if isinstance(tree.value, str):
             return compile_str(tree.value)
@@ -592,16 +593,26 @@ def compile(tree, ctx, indent=0):
         with open(filename) as file:
             outline = outlines.outline(AST39.parse(file.read(), filename))
 
+        to_import = []
+        to_bind = []
         for name in names:
             if name.isupper(): # Global constant
                 LAB_IMPORT_CONSTANTS.append(name)
-            if name[0].isupper(): # Class
+                to_import.append("constants as {}_constants".format(tree.module))
+                to_bind.append(name)
+            elif name[0].isupper(): # Class
                 LAB_IMPORT_CLASSES.append(name)
                 load_outline_for_class(outline, name)
+                to_import.append(name)
             else: # function
                 LAB_IMPORT_FNS.append(name)
+                to_import.append(name)
 
-        return " " * indent + "import {{ {} }} from \"./{}.js\";".format(", ".join(names), tree.module)
+        import_line = "import {{ {} }} from \"./{}.js\";".format(", ".join(sorted(set(to_import))), tree.module)
+        out = " " * indent + import_line
+        for const in to_bind:
+            out += "\n" + " " * indent + "constants.{} = {}_constants.{};".format(const, tree.module, const)
+        return out
     elif isinstance(tree, ast.ClassDef):
         assert not tree.bases
         assert not tree.keywords

infra/compiler.md

@@ -282,14 +282,22 @@ deduplicate the code a bit:
     import { request } from "./lab1.js";
     >>> assert "request" in LAB_IMPORT_FNS
     >>> Test.stmt("from lab2 import HSTEP")
-    import { HSTEP } from "./lab2.js";
+    import { constants as lab2_constants } from "./lab2.js";
+    constants.HSTEP = lab2_constants.HSTEP;
     >>> assert "HSTEP" in LAB_IMPORT_CONSTANTS
     >>> Test.stmt("from lab4 import Element")
     import { Element } from "./lab4.js";
-    >>> assert "HSTEP" in LAB_IMPORT_CLASSES
+    >>> assert "Element" in LAB_IMPORT_CLASSES
     >>> Test.stmt("from lab2 import WIDTH, HEIGHT, HSTEP, VSTEP")
-    import { WIDTH, HEIGHT, HSTEP, VSTEP } from "./lab2.js";
+    import { constants as lab2_constants } from "./lab2.js";
+    constants.WIDTH = lab2_constants.WIDTH;
+    constants.HEIGHT = lab2_constants.HEIGHT;
+    constants.HSTEP = lab2_constants.HSTEP;
+    constants.VSTEP = lab2_constants.VSTEP;
     >>> assert "WIDTH" in LAB_IMPORT_CONSTANTS
+    
+Note that `from ... import` statements for constants are complex, due
+to the use of a global collector object for constants.
 
 Functions become function definitions:
 

src/lab6.hints

@@ -2,6 +2,5 @@
 {"code": "'://' in url", "type": "str"},
 {"code": "self.s[self.i] in chars", "type": "list"},
 {"code": "'style' in node.attributes", "type": "dict"},
-{"code": "child.tag in BLOCK_ELEMENTS", "type": "list"},
 {"code": "'href' in node.attributes", "type": "dict"}
 ]

src/lab6.py

@@ -147,9 +147,8 @@ def matches(self, node):
         return False
 
     def __repr__(self):
-        return ("DescendantSelector(ancestor={}, " +
-            "descendant={}, priority={}").format(
-            self.ancestor, self.descendant, self.priority)
+        return ("DescendantSelector(ancestor={}, descendant={}, priority={}") \
+            .format(self.ancestor, self.descendant, self.priority)
 
 INHERITED_PROPERTIES = {
     "font-size": "16px",

src/lab7.py

@@ -13,8 +13,7 @@
 from lab3 import FONTS, get_font
 from lab4 import Text, Element, print_tree, HTMLParser
 from lab5 import BLOCK_ELEMENTS, layout_mode, DrawRect
-from lab6 import DocumentLayout, BlockLayout, InlineLayout, DrawText
-from lab6 import CSSParser, cascade_priority, style, resolve_url, tree_to_list
+from lab6 import DrawText, CSSParser, cascade_priority, style, resolve_url, tree_to_list
 
 class LineLayout:
     def __init__(self, node, parent, previous):

www/widgets/rt.js

@@ -223,6 +223,8 @@ static tkinter(options) {
             this.style = params.style ?? "normal";
             this.string = (this.style == "roman" ? "normal" : this.style) + 
                 " " + this.weight + " " + this.size * rt_constants.ZOOM + "px serif";
+
+            this.$metrics = null;
         }
 
         measure(text) {
@@ -232,28 +234,30 @@ static tkinter(options) {
         }
 
         metrics(field) {
-            let ctx = rt_constants.TKELEMENT.getContext('2d');
-            ctx.textBaseline = "alphabetic";
-            ctx.font = this.string;
-            let m = ctx.measureText("Hxy");
-            let asc, desc;
-
-            // Only Safari provides emHeight properties as of 2021-04
-            // We fake them in the other browsers by guessing that emHeight = font.size
-            // This is not quite right but is close enough for many fonts...
-            if (m.emHeightAscent && m.emHeightDescent) {
-                asc = ctx.measureText("Hxy").emHeightAscent / rt_constants.ZOOM;
-                desc = ctx.measureText("Hxy").emHeightDescent / rt_constants.ZOOM;
-            } else {
-                asc = ctx.measureText("Hxy").actualBoundingBoxAscent / rt_constants.ZOOM;
-                desc = ctx.measureText("Hxy").actualBoundingBoxDescent / rt_constants.ZOOM;
-                let gap = this.size - (asc + desc)
-                asc += gap / 2;
-                desc += gap / 2;
+            if (!this.$metrics) {
+                let ctx = rt_constants.TKELEMENT.getContext('2d');
+                ctx.textBaseline = "alphabetic";
+                ctx.font = this.string;
+                let m = ctx.measureText("Hxy");
+                let asc, desc;
+
+                // Only Safari provides emHeight properties as of 2021-04
+                // We fake them in the other browsers by guessing that emHeight = font.size
+                // This is not quite right but is close enough for many fonts...
+                if (m.emHeightAscent && m.emHeightDescent) {
+                    asc = ctx.measureText("Hxy").emHeightAscent / rt_constants.ZOOM;
+                    desc = ctx.measureText("Hxy").emHeightDescent / rt_constants.ZOOM;
+                } else {
+                    asc = ctx.measureText("Hxy").actualBoundingBoxAscent / rt_constants.ZOOM;
+                    desc = ctx.measureText("Hxy").actualBoundingBoxDescent / rt_constants.ZOOM;
+                    let gap = this.size - (asc + desc)
+                    asc += gap / 2;
+                    desc += gap / 2;
+                }
+                this.$metrics = { ascent: asc, descent: desc, linespace: asc + desc, fixed: 0 };
             }
-            let obj = { ascent: asc, descent: desc, linespace: asc + desc, fixed: 0 };
-            if (field) return obj[field]
-            else return obj;
+            if (field) return this.$metrics[field]
+            else return this.$metrics;
         }
     }