[IMP] web: implement formatAST utility function

In this commit, we implement a function which format a py.js abstract
syntax tree into a string.  This is really useful whenever we need to
manipulate python expressions.

1 files changed, 93 insertions, 0 deletions

diff --git a/addons/web/static/src/js/core/py_utils.js b/addons/web/static/src/js/core/py_utils.js
index 8590965cee2..c077cfc2e7e 100644
--- a/addons/web/static/src/js/core/py_utils.js
+++ b/addons/web/static/src/js/core/py_utils.js
@@ -314,6 +314,98 @@ function py_eval(expr, context) {
     return py.eval(expr, _.extend({}, context || {}, {"true": true, "false": false, "null": null}));
 }
 
+// Binding power for prefix operator is not accessible in the AST generated by
+// py.js, so we have to hardcode some values here
+var BINDING_POWERS = {
+    or: 30,
+    and: 40,
+    not: 50,
+};
+
+/**
+ * Convert a python AST (generated by py.js) to a string form, which should
+ * represent the same AST.
+ *
+ * @param {Object} ast a valid AST obtained by py.js, which represent a python
+ *   expression
+ * @param {integer} [lbp=0] a binding power. This is necessary to be able to
+ *   format sub expressions: the + sub expression in "3 * (a + 2)" should be
+ *   formatted with parenthesis, because its binding power is lower than the
+ *   binding power of *.
+ * @returns {string}
+ */
+function formatAST(ast, lbp) {
+    lbp = lbp || 0;
+    switch (ast.id) {
+        // basic values
+        case "(number)":
+            return String(ast.value);
+        case "(string)":
+            return "'" + ast.value + "'";
+        case "(constant)":
+            return ast.value;
+        case "(name)":
+            return ast.value;
+        case "[":
+            if (ast.second) {
+                // read a value in a dictionary: d['a']
+                return formatAST(ast.first) + '[' + formatAST(ast.second) + ']';
+            } else {
+                // list: [1, 2]
+                var values = ast.first.map(formatAST);
+                return '[' + values.join(', ') + ']';
+            }
+        case "{":
+            var keyValues = ast.first.map(function (kv) {
+                return formatAST(kv[0]) + ': ' + formatAST(kv[1]);
+            });
+            return '{' + keyValues.join(', ') + '}';
+
+        // relations
+        case "=":
+            return formatAST(ast.first) + ' ' + ast.id + ' ' + formatAST(ast.second);
+        // operators
+        case "-":
+        case "+":
+        case "~":
+        case "*":
+        case "**":
+        case "%":
+        case "//":
+        case "and":
+        case "or":
+            if (ast.second) {
+                // infix
+                var r = formatAST(ast.first, ast.lbp) + ' ' + ast.id + ' ' + formatAST(ast.second, ast.lbp);
+                if (ast.lbp < lbp) {
+                    r = '(' + r + ')';
+                }
+                return r;
+            }
+            // prefix
+            // real lbp is not accessible, it is inside a closure
+            var actualBP = BINDING_POWERS[ast.id] || 130;
+            return ast.id + formatAST(ast.first, actualBP);
+        case ".":
+            return formatAST(ast.first, ast.lbp) + '.' + formatAST(ast.second);
+        case "not":
+            return "not " + formatAST(ast.first);
+        case "(comparator)":
+            var operator = ast.operators[0]
+            return formatAST(ast.expressions[0]) + ' ' + operator + ' ' + formatAST(ast.expressions[1]);
+
+        // function call
+        case "(":
+            if (ast.second) {
+                // this is a function call: f(a, b)
+                return formatAST(ast.first) + '(' + ast.second.map(formatAST).join(', ') + ')';
+            } else {
+                // this is a tuple
+                return '(' + ast.first.map(formatAST).join(', ') + ')';
+            }
+    }
+    throw new Error("Unimplemented python construct");
+}
 
 return {
     context: pycontext,
@@ -321,6 +413,7 @@ return {
     eval: pyeval,
     eval_domains_and_contexts: eval_domains_and_contexts,
     py_eval: py_eval,
+    formatAST: formatAST,
 };
 
 });