docs: add check code output for result="ansi" (#3435)

* Add ast parsing to determine whether we should include result="ansi".
It's not meant to be perfect, but will hopefully catch the most common
cases. Still requires manual review.
* Ideally we could suppress output in markdown-exec in the future.

docs/_scripts/notebook_convert.py

@@ -64,6 +64,100 @@ def _rewrite_cell_magic(code: str) -> str:
     return "\n".join(rewritten_lines)
 
 
+class PrintCallVisitor(ast.NodeVisitor):
+    """
+    This visitor sets self.has_print to True if it encounters a call
+    to a print within the global scope.
+
+    This should catch calls to print(), print_stream(), etc. (Prefixed with "print").
+
+    May have some false positives, but it's not meant to be perfect.
+
+    Temporary code for notebook conversion.
+    """
+
+    def __init__(self):
+        self.has_print = False
+        self.scope_level = 0  # counter to track whether we're inside a def/lambda
+
+    def visit_FunctionDef(self, node):
+        self.scope_level += 1
+        self.generic_visit(node)
+        self.scope_level -= 1
+
+    def visit_AsyncFunctionDef(self, node):
+        self.scope_level += 1
+        self.generic_visit(node)
+        self.scope_level -= 1
+
+    def visit_Lambda(self, node):
+        self.scope_level += 1
+        self.generic_visit(node)
+        self.scope_level -= 1
+
+    def visit_ClassDef(self, node):
+        self.scope_level += 1
+        self.generic_visit(node)
+        self.scope_level -= 1
+
+    def visit_Call(self, node):
+        # Only consider calls when not inside a function definition.
+        if self.scope_level == 0:
+            if isinstance(node.func, ast.Name) and node.func.id.startswith("print"):
+                self.has_print = True
+        self.generic_visit(node)
+
+
+def _has_output(source: str) -> bool:
+    """Determine if the code block is expected to produce output.
+
+    Args:
+        source (str): The source code of the code block.
+
+    Returns:
+        True if the code block is expected to produce output, False otherwise.
+
+        Must meet the following conditions:
+
+        1. There is a call to a printing function (name starts with "print")
+           that is not inside a function definition.
+        2. The last top-level statement is an expression that is valid if:
+         - It is any expression (including calls) AND
+         - It is NOT a call to `display(...)`.
+
+        `display` isn't handled currently by markdown-exec
+    """
+    try:
+        tree = ast.parse(source)
+    except SyntaxError:
+        return False
+
+    # Condition (1): Check for a global print-like call.
+    visitor = PrintCallVisitor()
+    visitor.visit(tree)
+    condition_a = visitor.has_print
+
+    # Condition (2): Check the last top-level statement.
+    condition_b = False
+    if tree.body:
+        last_stmt = tree.body[-1]
+        if isinstance(last_stmt, ast.Expr):
+            # If the expression is a call, ensure it's not a call to "display"
+            if isinstance(last_stmt.value, ast.Call):
+                if (
+                    isinstance(last_stmt.value.func, ast.Name)
+                    and last_stmt.value.func.id == "display"
+                ):
+                    condition_b = False  # exclude display-wrapped expressions
+                else:
+                    condition_b = True
+            else:
+                # Any other expression qualifies.
+                condition_b = True
+
+    return condition_a or condition_b
+
+
 def _convert_links_in_markdown(markdown: str) -> str:
     """Convert links present in notebook markdown cells to standardized format.
 
@@ -161,6 +255,8 @@ class EscapePreprocessor(Preprocessor):
                     cell.source = _rewrite_cell_magic(source)
                     cell.metadata["language"] = "shell"
 
+                cell.metadata["has_output"] = _has_output(source)
+
             # Remove noqa comments
             cell.source = re.sub(r"#\s*noqa.*$", "", cell.source, flags=re.MULTILINE)
             # escape ``` in code

docs/_scripts/notebook_convert_templates/md_executable/index.md.j2

@@ -8,7 +8,7 @@
 {%- elif cell.metadata.get('language') == "shell" -%}
     shell
 {%- elif 'name' in nb.metadata.get('language_info', {}) -%}
-    {{ nb.metadata.language_info.name }}{% if cell.metadata.exec|default(false) %} exec="on" source="above" session="1" result="ansi"{% endif %}
+    {{ nb.metadata.language_info.name }}{% if cell.metadata.exec|default(false) %} exec="on" source="above" session="1"{% if cell.metadata.has_output|default(false) %} result="ansi"{% endif %}{% endif %}
 {%- endif %}
 {{ cell.source}}
 ```