RustPython · coolreader18 · May 5, 2020 · Apr 28, 2020 · Apr 29, 2020 · Apr 29, 2020
diff --git a/parser/src/fstring.rs b/parser/src/fstring.rs
@@ -26,9 +26,33 @@ impl<'a> FStringParser<'a> {
         let mut spec = None;
         let mut delims = Vec::new();
         let mut conversion = None;
+        let mut pred_expression_text = String::new();
+        let mut trailing_seq = String::new();
 
         while let Some(ch) = self.chars.next() {
             match ch {
+                // can be integrated better with the remainign code, but as a starting point ok
+                // in general I would do here a tokenizing of the fstrings to omit this peeking.
+                '!' if self.chars.peek() == Some(&'=') => {
+                    expression.push_str("!=");
+                    self.chars.next();
+                }
+
+                '=' if self.chars.peek() == Some(&'=') => {
+                    expression.push_str("==");
+                    self.chars.next();
+                }
+
+                '>' if self.chars.peek() == Some(&'=') => {
+                    expression.push_str(">=");
+                    self.chars.next();
+                }
+
+                '<' if self.chars.peek() == Some(&'=') => {
+                    expression.push_str("<=");
+                    self.chars.next();
+                }
+
                 '!' if delims.is_empty() && self.chars.peek() != Some(&'=') => {
                     if expression.trim().is_empty() {
                         return Err(EmptyExpression);
@@ -46,10 +70,22 @@ impl<'a> FStringParser<'a> {
                         }
                     });
 
-                    if self.chars.peek() != Some(&'}') {
+                    if let Some(&peek) = self.chars.peek() {
+                        if peek != '}' && peek != ':' {
+                            return Err(ExpectedRbrace);
+                        }
+                    } else {
                         return Err(ExpectedRbrace);
                     }
                 }
+
+                // match a python 3.8 self documenting expression
+                // format '{' PYTHON_EXPRESSION '=' FORMAT_SPECIFIER? '}'
+                '=' if self.chars.peek() != Some(&'=') => {
+                    // check for delims empty?
+                    pred_expression_text = expression.to_string(); // safe expression before = to print it
+                }
+
                 ':' if delims.is_empty() => {
                     let mut nested = false;
                     let mut in_nested = false;
@@ -121,14 +157,35 @@ impl<'a> FStringParser<'a> {
                     if expression.is_empty() {
                         return Err(EmptyExpression);
                     }
-                    return Ok(FormattedValue {
-                        value: Box::new(
-                            parse_expression(expression.trim())
-                                .map_err(|e| InvalidExpression(Box::new(e.error)))?,
-                        ),
-                        conversion,
-                        spec,
-                    });
+                    if pred_expression_text.is_empty() {
+                        return Ok(FormattedValue {
+                            value: Box::new(
+                                parse_expression(expression.trim())
+                                    .map_err(|e| InvalidExpression(Box::new(e.error)))?,
+                            ),
+                            conversion,
+                            spec,
+                        });
+                    } else {
+                        return Ok(Joined {
+                            values: vec![
+                                Constant {
+                                    value: pred_expression_text + "=",
+                                },
+                                Constant {
+                                    value: trailing_seq,
+                                },
+                                FormattedValue {
+                                    value: Box::new(
+                                        parse_expression(expression.trim())
+                                            .map_err(|e| InvalidExpression(Box::new(e.error)))?,
+                                    ),
+                                    conversion,
+                                    spec,
+                                },
+                            ],
+                        });
+                    }
                 }
                 '"' | '\'' => {
                     expression.push(ch);
@@ -139,12 +196,14 @@ impl<'a> FStringParser<'a> {
                         }
                     }
                 }
+                ' ' if !pred_expression_text.is_empty() => {
+                    trailing_seq.push(ch);
+                }
                 _ => {
                     expression.push(ch);
                 }
             }
         }
-
         Err(UnclosedLbrace)
     }
 
@@ -298,12 +357,35 @@ mod tests {
         );
     }
 
+    #[test]
+    fn test_fstring_parse_selfdocumenting_base() {
+        let src = String::from("{user=}");
+        let parse_ast = parse_fstring(&src);
+
+        assert!(parse_ast.is_ok());
+    }
+
+    #[test]
+    fn test_fstring_parse_selfdocumenting_base_more() {
+        let src = String::from("mix {user=} with text and {second=}");
+        let parse_ast = parse_fstring(&src);
+
+        assert!(parse_ast.is_ok());
+    }
+
+    #[test]
+    fn test_fstring_parse_selfdocumenting_format() {
+        let src = String::from("{user=:>10}");
+        let parse_ast = parse_fstring(&src);
+
+        assert!(parse_ast.is_ok());
+    }
+
     #[test]
     fn test_parse_invalid_fstring() {
         assert_eq!(parse_fstring("{5!a"), Err(ExpectedRbrace));
         assert_eq!(parse_fstring("{5!a1}"), Err(ExpectedRbrace));
         assert_eq!(parse_fstring("{5!"), Err(ExpectedRbrace));
-
         assert_eq!(parse_fstring("abc{!a 'cat'}"), Err(EmptyExpression));
         assert_eq!(parse_fstring("{!a"), Err(EmptyExpression));
         assert_eq!(parse_fstring("{ !a}"), Err(EmptyExpression));
@@ -318,6 +400,8 @@ mod tests {
         assert_eq!(parse_fstring("{a:{b}"), Err(UnclosedLbrace));
         assert_eq!(parse_fstring("{"), Err(UnclosedLbrace));
 
+        assert_eq!(parse_fstring("{}"), Err(EmptyExpression));
+
         // TODO: check for InvalidExpression enum?
         assert!(parse_fstring("{class}").is_err());
     }
@@ -328,4 +412,25 @@ mod tests {
         let parse_ast = parse_fstring(&source);
         assert!(parse_ast.is_ok());
     }
+
+    #[test]
+    fn test_parse_fstring_equals() {
+        let source = String::from("{42 == 42}");
+        let parse_ast = parse_fstring(&source);
+        assert!(parse_ast.is_ok());
+    }
+
+    #[test]
+    fn test_parse_fstring_selfdoc_prec_space() {
+        let source = String::from("{x   =}");
+        let parse_ast = parse_fstring(&source);
+        assert!(parse_ast.is_ok());
+    }
+
+    #[test]
+    fn test_parse_fstring_selfdoc_trailing_space() {
+        let source = String::from("{x=   }");
+        let parse_ast = parse_fstring(&source);
+        assert!(parse_ast.is_ok());
+    }
 }
diff --git a/tests/snippets/fstrings.py b/tests/snippets/fstrings.py
@@ -1,4 +1,19 @@
 from testutils import assert_raises
+
+#test only makes sense with python 3.8 or higher (or RustPython)
+import sys
+import platform
+if platform.python_implementation() == 'CPython':
+    assert sys.version_info >= (3, 8), 'Incompatible Python Version, expected CPython 3.8 or later'
+elif platform.python_implementation == 'RustPython':
+    # ok
+    pass
+else:
+    # other implementation - lets give it a try
+    pass
+
+
+# lets start tersing
 foo = 'bar'
 
 assert f"{''}" == ''
@@ -17,6 +32,18 @@
 assert f'{16:0>+#10x}' == '00000+0x10'
 assert f"{{{(lambda x: f'hello, {x}')('world}')}" == '{hello, world}'
 
+
+# base test of self documenting strings
+#assert f'{foo=}' == 'foo=bar' # TODO ' missing
+
+num=42
+
+f'{num=}' # keep this line as it will fail when using a python 3.7 interpreter 
+
+assert f'{num=}' == 'num=42'
+assert f'{num=:>10}' == 'num=        42'
+
+
 spec = "0>+#10x"
 assert f"{16:{spec}}{foo}" == '00000+0x10bar'
 
@@ -61,3 +88,84 @@ def __str__(self):
 assert f'>{v!r}' == ">'\u262e'"
 assert f'>{v!s}' == '>\u262e'
 assert f'>{v!a}' == r">'\u262e'"
+
+
+
+# Test format specifier after conversion flag
+#assert f'{"42"!s:<5}' == '42   ', '#' + f'{"42"!s:5}' +'#' # TODO: default alignment in cpython is left
+
+assert f'{"42"!s:<5}' == '42   ', '#' + f'{"42"!s:<5}' +'#'
+assert f'{"42"!s:>5}' == '   42', '#' + f'{"42"!s:>5}' +'#'
+
+#assert f'{"42"=!s:5}' == '"42"=42   ', '#'+ f'{"42"=!s:5}' +'#' # TODO default alingment in cpython is left
+assert f'{"42"=!s:<5}' == '"42"=42   ', '#'+ f'{"42"=!s:<5}' +'#'
+assert f'{"42"=!s:>5}' == '"42"=   42', '#'+ f'{"42"=!s:>5}' +'#'
+
+
+
+### Tests for fstring selfdocumenting form CPython
+
+class C:
+    def assertEqual(self, a,b):
+        assert a==b, "{0} == {1}".format(a,b)
+
+self=C()
+
+x = 'A string'
+self.assertEqual(f'{10=}', '10=10')
+# self.assertEqual(f'{x=}', 'x=' + x )#repr(x)) # TODO: add  ' when printing strings
+# self.assertEqual(f'{x =}', 'x =' + x )# + repr(x)) # TODO: implement '  handling
+self.assertEqual(f'{x=!s}', 'x=' + str(x))
+# # self.assertEqual(f'{x=!r}', 'x=' + x) #repr(x)) # !r not supported
+# self.assertEqual(f'{x=!a}', 'x=' + ascii(x))
+
+x = 2.71828
+self.assertEqual(f'{x=:.2f}', 'x=' + format(x, '.2f'))
+self.assertEqual(f'{x=:}', 'x=' + format(x, ''))
+self.assertEqual(f'{x=!r:^20}', 'x=' + format(repr(x), '^20')) #TODO formatspecifier after conversion flsg is currently not supported (also for classical fstrings)
+self.assertEqual(f'{x=!s:^20}', 'x=' + format(str(x), '^20'))
+self.assertEqual(f'{x=!a:^20}', 'x=' + format(ascii(x), '^20'))
+
+x = 9
+self.assertEqual(f'{3*x+15=}', '3*x+15=42')
+
+# There is code in ast.c that deals with non-ascii expression values.  So,
+# use a unicode identifier to trigger that.
+tenπ = 31.4
+self.assertEqual(f'{tenπ=:.2f}', 'tenπ=31.40')
+
+# Also test with Unicode in non-identifiers.
+#self.assertEqual(f'{"Σ"=}', '"Σ"=\'Σ\'') ' TODO ' missing
+
+# Make sure nested fstrings still work.
+self.assertEqual(f'{f"{3.1415=:.1f}":*^20}', '*****3.1415=3.1*****')
+
+# Make sure text before and after an expression with = works
+# correctly.
+pi = 'π'
+#self.assertEqual(f'alpha α {pi=} ω omega', "alpha α pi='π' ω omega") # ' missing around pi
+
+# Check multi-line expressions.
+#self.assertEqual(f'''{3=}''', '\n3\n=3') # TODO: multiline f strings not supported, seems to be an rustpython issue
+
+# Since = is handled specially, make sure all existing uses of
+# it still work.
+
+self.assertEqual(f'{0==1}', 'False')
+self.assertEqual(f'{0!=1}', 'True')
+self.assertEqual(f'{0<=1}', 'True')
+self.assertEqual(f'{0>=1}', 'False')
+
+# Make sure leading and following text works.
+# x = 'foo'
+#self.assertEqual(f'X{x=}Y', 'Xx='+repr(x)+'Y') # TODO ' 
+# self.assertEqual(f'X{x=}Y', 'Xx='+x+'Y') # just for the moment
+
+# Make sure whitespace around the = works.
+# self.assertEqual(f'X{x  =}Y', 'Xx  ='+repr(x)+'Y')  # TODO '
+# self.assertEqual(f'X{x=  }Y', 'Xx=  '+repr(x)+'Y') # TODO '
+# self.assertEqual(f'X{x  =  }Y', 'Xx  =  '+repr(x)+'Y') # TODO '
+
+# self.assertEqual(f'X{x  =}Y', 'Xx  ='+x+'Y')
+# self.assertEqual(f'X{x=  }Y', 'Xx=  '+x+'Y')
+# self.assertEqual(f'X{x  =  }Y', 'Xx  =  '+x+'Y')