RustPython · coolreader18 · Dec 28, 2019 · Dec 13, 2019 · Dec 14, 2019 · Dec 21, 2019
diff --git a/bytecode/src/bytecode.rs b/bytecode/src/bytecode.rs
@@ -274,7 +274,6 @@ pub enum Instruction {
     },
     FormatValue {
         conversion: Option<ConversionFlag>,
-        spec: String,
     },
     PopException,
     Reverse {
@@ -564,7 +563,7 @@ impl Instruction {
             LoadBuildClass => w!(LoadBuildClass),
             UnpackSequence { size } => w!(UnpackSequence, size),
             UnpackEx { before, after } => w!(UnpackEx, before, after),
-            FormatValue { spec, .. } => w!(FormatValue, spec), // TODO: write conversion
+            FormatValue { .. } => w!(FormatValue), // TODO: write conversion
             PopException => w!(PopException),
             Reverse { amount } => w!(Reverse, amount),
             GetAwaitable => w!(GetAwaitable),

diff --git a/compiler/src/compile.rs b/compiler/src/compile.rs
@@ -2108,10 +2108,17 @@ impl<O: OutputStream> Compiler<O> {
                     conversion,
                     spec,
                 } => {
+                    match spec {
+                        Some(spec) => self.compile_string(spec)?,
+                        None => self.emit(Instruction::LoadConst {
+                            value: bytecode::Constant::String {
+                                value: String::new(),
+                            },
+                        }),
+                    };
                     self.compile_expression(value)?;
                     self.emit(Instruction::FormatValue {
                         conversion: conversion.map(compile_conversion_flag),
-                        spec: spec.clone(),
                     });
                 }
             }

diff --git a/compiler/src/symboltable.rs b/compiler/src/symboltable.rs
@@ -726,8 +726,11 @@ impl SymbolTableBuilder {
     fn scan_string_group(&mut self, group: &ast::StringGroup) -> SymbolTableResult {
        match group {
             ast::StringGroup::Constant { .. } => {}
-            ast::StringGroup::FormattedValue { value, .. } => {
+            ast::StringGroup::FormattedValue { value, spec, .. } => {
                 self.scan_expression(value, &ExpressionContext::Load)?;
+                if let Some(spec) = spec {
+                    self.scan_string_group(spec)?;
+                }
             }
             ast::StringGroup::Joined { values } => {
                 for subgroup in values {

diff --git a/parser/src/ast.rs b/parser/src/ast.rs
@@ -505,7 +505,7 @@ pub enum StringGroup {
     FormattedValue {
         value: Box<Expression>,
         conversion: Option<ConversionFlag>,
-        spec: String,
+        spec: Option<Box<StringGroup>>,
     },
     Joined {
         values: Vec<StringGroup>,

diff --git a/parser/src/error.rs b/parser/src/error.rs
@@ -81,6 +81,7 @@ pub enum FStringErrorType {
     InvalidConversionFlag,
     EmptyExpression,
     MismatchedDelimiter,
+    ExpressionNestedTooDeeply,
 }
 
 impl fmt::Display for FStringErrorType {
@@ -94,6 +95,9 @@ impl fmt::Display for FStringErrorType {
             FStringErrorType::InvalidConversionFlag => write!(f, "Invalid conversion flag"),
             FStringErrorType::EmptyExpression => write!(f, "Empty expression"),
             FStringErrorType::MismatchedDelimiter => write!(f, "Mismatched delimiter"),
+            FStringErrorType::ExpressionNestedTooDeeply => {
+                write!(f, "expressions nested too deeply")
+            }
         }
     }
 }

diff --git a/parser/src/fstring.rs b/parser/src/fstring.rs
@@ -23,7 +23,7 @@ impl<'a> FStringParser<'a> {
 
     fn parse_formatted_value(&mut self) -> Result<StringGroup, FStringErrorType> {
         let mut expression = String::new();
-        let mut spec = String::new();
+        let mut spec = None;
         let mut delims = Vec::new();
         let mut conversion = None;
 
@@ -43,13 +43,48 @@ impl<'a> FStringParser<'a> {
                     })
                 }
                 ':' if delims.is_empty() => {
+                    let mut nested = false;
+                    let mut in_nested = false;
+                    let mut spec_expression = String::new();
                     while let Some(&next) = self.chars.peek() {
-                        if next != '}' {
-                            spec.push(next);
-                            self.chars.next();
-                        } else {
-                            break;
+                        match next {
+                            '{' => {
+                                if in_nested {
+                                    return Err(ExpressionNestedTooDeeply);
+                                }
+                                in_nested = true;
+                                nested = true;
+                                self.chars.next();
+                                continue;
+                            }
+                            '}' => {
+                                if in_nested {
+                                    in_nested = false;
+                                    self.chars.next();
+                                }
+                                break;
+                            }
+                            _ => (),
                         }
+                        spec_expression.push(next);
+                        self.chars.next();
+                    }
+                    if in_nested {
+                        return Err(UnclosedLbrace);
+                    }
+                    if nested {
+                        spec = Some(Box::new(FormattedValue {
+                            value: Box::new(
+                                parse_expression(spec_expression.trim())
+                                    .map_err(|e| InvalidExpression(Box::new(e.error)))?,
+                            ),
+                            conversion: None,
+                            spec: None,
+                        }))
+                    } else {
+                        spec = Some(Box::new(Constant {
+                            value: spec_expression.trim().to_string(),
+                        }))
                     }
                 }
                 '(' | '{' | '[' => {
@@ -194,12 +229,12 @@ mod tests {
                     FormattedValue {
                         value: Box::new(mk_ident("a", 1, 1)),
                         conversion: None,
-                        spec: String::new(),
+                        spec: None,
                     },
                     FormattedValue {
                         value: Box::new(mk_ident("b", 1, 1)),
                         conversion: None,
-                        spec: String::new(),
+                        spec: None,
                     },
                     Constant {
                         value: "{foo}".to_owned()
@@ -209,6 +244,42 @@ mod tests {
         );
     }
 
+    #[test]
+    fn test_parse_fstring_nested_spec() {
+        let source = String::from("{foo:{spec}}");
+        let parse_ast = parse_fstring(&source).unwrap();
+
+        assert_eq!(
+            parse_ast,
+            FormattedValue {
+                value: Box::new(mk_ident("foo", 1, 1)),
+                conversion: None,
+                spec: Some(Box::new(FormattedValue {
+                    value: Box::new(mk_ident("spec", 1, 1)),
+                    conversion: None,
+                    spec: None,
+                })),
+            }
+        );
+    }
+
+    #[test]
+    fn test_parse_fstring_not_nested_spec() {
+        let source = String::from("{foo:spec}");
+        let parse_ast = parse_fstring(&source).unwrap();
+
+        assert_eq!(
+            parse_ast,
+            FormattedValue {
+                value: Box::new(mk_ident("foo", 1, 1)),
+                conversion: None,
+                spec: Some(Box::new(Constant {
+                    value: "spec".to_string(),
+                })),
+            }
+        );
+    }
+
     #[test]
     fn test_parse_empty_fstring() {
         assert_eq!(
@@ -223,6 +294,9 @@ mod tests {
     fn test_parse_invalid_fstring() {
         assert_eq!(parse_fstring("{"), Err(UnclosedLbrace));
         assert_eq!(parse_fstring("}"), Err(UnopenedRbrace));
+        assert_eq!(parse_fstring("{a:{a:{b}}"), Err(ExpressionNestedTooDeeply));
+        assert_eq!(parse_fstring("{a:b}}"), Err(UnopenedRbrace));
+        assert_eq!(parse_fstring("{a:{b}"), Err(UnclosedLbrace));
 
         // TODO: check for InvalidExpression enum?
         assert!(parse_fstring("{class}").is_err());

diff --git a/tests/snippets/fstrings.py b/tests/snippets/fstrings.py
@@ -1,3 +1,4 @@
+from testutils import assert_raises
 foo = 'bar'
 
 assert f"{''}" == ''
@@ -16,6 +17,13 @@
 assert f'{16:0>+#10x}' == '00000+0x10'
 assert f"{{{(lambda x: f'hello, {x}')('world}')}" == '{hello, world}'
 
+spec = "0>+#10x"
+assert f"{16:{spec}}{foo}" == '00000+0x10bar'
+
+# TODO:
+# spec = "bla"
+# assert_raises(ValueError, lambda: f"{16:{spec}}")
+
 # Normally `!` cannot appear outside of delimiters in the expression but
 # cpython makes an exception for `!=`, so we should too.
 

diff --git a/vm/src/frame.rs b/vm/src/frame.rs
@@ -616,7 +616,7 @@ impl Frame {
             bytecode::Instruction::UnpackEx { before, after } => {
                 self.execute_unpack_ex(vm, *before, *after)
             }
-            bytecode::Instruction::FormatValue { conversion, spec } => {
+            bytecode::Instruction::FormatValue { conversion } => {
                 use bytecode::ConversionFlag::*;
                 let value = match conversion {
                     Some(Str) => vm.to_str(&self.pop_value())?.into_object(),
@@ -625,7 +625,7 @@ impl Frame {
                     None => self.pop_value(),
                 };
 
-                let spec = vm.new_str(spec.clone());
+                let spec = vm.to_str(&self.pop_value())?.into_object();
                 let formatted = vm.call_method(&value, "__format__", vec![spec])?;
                 self.push_value(formatted);
                 Ok(None)