10 files changed, 138 insertions, 5 deletions
diff --git a/tests/basics/string_fstring.py b/tests/basics/string_fstring.py
new file mode 100644
index 000000000..efb7e5a8e
--- /dev/null
+++ b/tests/basics/string_fstring.py
@@ -0,0 +1,57 @@
+def f():
+    return 4
+def g(_):
+    return 5
+def h():
+    return 6
+
+print(f'no interpolation')
+print(f"no interpolation")
+print(f"""no interpolation""")
+
+x, y = 1, 2
+print(f'{x}')
+print(f'{x:08x}')
+print(f'{x=}')
+print(f'{x=:08x}')
+print(f'a {x} b {y} c')
+print(f'a {x:08x} b {y} c')
+print(f'a {x=} b {y} c')
+print(f'a {x=:08x} b {y} c')
+
+print(f'a {"hello"} b')
+print(f'a {f() + g("foo") + h()} b')
+print(f'a {f() + g("foo") + h()=} b')
+print(f'a {f() + g("foo") + h()=:08x} b')
+
+def foo(a, b):
+    return f'{x}{y}{a}{b}'
+print(foo(7, 8))
+
+# PEP-0498 specifies that '\\' and '#' must be disallowed explicitly, whereas
+# MicroPython relies on the syntax error as a result of the substitution.
+
+print(f"\\")
+print(f'#')
+try:
+    eval("f'{\}'")
+except SyntaxError:
+    print('SyntaxError')
+try:
+    eval("f'{#}'")
+except SyntaxError:
+    print('SyntaxError')
+
+
+# PEP-0498 specifies that handling of double braces '{{' or '}}' should
+# behave like str.format.
+print(f'{{}}')
+print(f'{{{4*10}}}', '{40}')
+
+# A single closing brace, unlike str.format should raise a syntax error.
+# MicroPython instead raises ValueError at runtime from the substitution.
+try:
+    eval("f'{{}'")
+except (ValueError, SyntaxError):
+    # MicroPython incorrectly raises ValueError here.
+    print('SyntaxError')
diff --git a/tests/cmdline/cmd_parsetree.py b/tests/cmdline/cmd_parsetree.py
index 50da36954..483ea8937 100644
--- a/tests/cmdline/cmd_parsetree.py
+++ b/tests/cmdline/cmd_parsetree.py
@@ -10,3 +10,4 @@ d = b"bytes"
 e = b"a very long bytes that will not be interned"
 f = 123456789012345678901234567890
 g = 123
+h = f"fstring: '{b}'"
diff --git a/tests/cmdline/cmd_parsetree.py.exp b/tests/cmdline/cmd_parsetree.py.exp
index e64f4f782..cc8ba82c0 100644
--- a/tests/cmdline/cmd_parsetree.py.exp
+++ b/tests/cmdline/cmd_parsetree.py.exp
@@ -1,6 +1,6 @@
 ----------------
-[   4] \(rule\|file_input_2\)(1) (n=9)
-         tok(4)
+[   4] \(rule\|file_input_2\)(1) (n=10)
+         tok(6)
 [   4]   \(rule\|for_stmt\)(22) (n=4)
            id(i)
 [   4]     \(rule\|atom_paren\)(45) (n=1)
@@ -9,7 +9,7 @@
            NULL
 [   6]   \(rule\|expr_stmt\)(5) (n=2)
            id(a)
-           tok(14)
+           tok(16)
 [   7]   \(rule\|expr_stmt\)(5) (n=2)
            id(b)
            str(str)
@@ -28,6 +28,16 @@
 [  12]   \(rule\|expr_stmt\)(5) (n=2)
            id(g)
            int(123)
+[  13]   \(rule\|expr_stmt\)(5) (n=2)
+           id(h)
+[  13]     \(rule\|atom_expr_normal\)(44) (n=2)
+[  13]       literal const(\.\+)
+[  13]       \(rule\|atom_expr_trailers\)(142) (n=2)
+[  13]         \(rule\|trailer_period\)(50) (n=1)
+                 id(format)
+[  13]         \(rule\|trailer_paren\)(48) (n=1)
+[  13]           \(rule\|arglist\)(164) (n=1)
+                   id(b)
 ----------------
 File cmdline/cmd_parsetree.py, code block '<module>' (descriptor: \.\+, bytecode @\.\+ bytes)
 Raw bytecode (code_info_size=\\d\+, bytecode_size=\\d\+):
@@ -46,6 +56,7 @@ arg names:
   bc=32 line=10
   bc=37 line=11
   bc=42 line=12
+  bc=48 line=13
 00 BUILD_TUPLE 0
 02 GET_ITER_STACK
 03 FOR_ITER 12
@@ -65,8 +76,13 @@ arg names:
 39 STORE_NAME f
 42 LOAD_CONST_SMALL_INT 123
 45 STORE_NAME g
-48 LOAD_CONST_NONE
-49 RETURN_VALUE
+48 LOAD_CONST_OBJ \.\+
+50 LOAD_METHOD format
+53 LOAD_NAME b (cache=0)
+57 CALL_METHOD n=1 nkw=0
+59 STORE_NAME h
+62 LOAD_CONST_NONE
+63 RETURN_VALUE
 mem: total=\\d\+, current=\\d\+, peak=\\d\+
 stack: \\d\+ out of \\d\+
 GC: total: \\d\+, used: \\d\+, free: \\d\+
diff --git a/tests/cpydiff/core_fstring_concat.py b/tests/cpydiff/core_fstring_concat.py
new file mode 100644
index 000000000..fd83527b5
--- /dev/null
+++ b/tests/cpydiff/core_fstring_concat.py
@@ -0,0 +1,12 @@
+"""
+categories: Core
+description: f-strings don't support concatenation with adjacent literals if the adjacent literals contain braces
+cause: MicroPython is optimised for code space.
+workaround: Use the + operator between literal strings when either is an f-string
+"""
+
+x = 1
+print("aa" f"{x}")
+print(f"{x}" "ab")
+print("a{}a" f"{x}")
+print(f"{x}" "a{}b")
diff --git a/tests/cpydiff/core_fstring_parser.py b/tests/cpydiff/core_fstring_parser.py
new file mode 100644
index 000000000..6917f3cfa
--- /dev/null
+++ b/tests/cpydiff/core_fstring_parser.py
@@ -0,0 +1,9 @@
+"""
+categories: Core
+description: f-strings cannot support expressions that require parsing to resolve nested braces
+cause: MicroPython is optimised for code space.
+workaround: Only use simple expressions inside f-strings
+"""
+
+f'{"hello {} world"}'
+f"{repr({})}"
diff --git a/tests/cpydiff/core_fstring_raw.py b/tests/cpydiff/core_fstring_raw.py
new file mode 100644
index 000000000..84e265f70
--- /dev/null
+++ b/tests/cpydiff/core_fstring_raw.py
@@ -0,0 +1,8 @@
+"""
+categories: Core
+description: Raw f-strings are not supported
+cause: MicroPython is optimised for code space.
+workaround: Unknown
+"""
+
+rf"hello"
diff --git a/tests/cpydiff/core_fstring_repr.py b/tests/cpydiff/core_fstring_repr.py
new file mode 100644
index 000000000..fcadcbf1b
--- /dev/null
+++ b/tests/cpydiff/core_fstring_repr.py
@@ -0,0 +1,18 @@
+"""
+categories: Core
+description: f-strings don't support the !r, !s, and !a conversions
+cause: MicroPython is optimised for code space.
+workaround: Use repr(), str(), and ascii() explictly.
+"""
+
+
+class X:
+    def __repr__(self):
+        return "repr"
+
+    def __str__(self):
+        return "str"
+
+
+print(f"{X()!r}")
+print(f"{X()!s}")
diff --git a/tests/feature_check/fstring.py b/tests/feature_check/fstring.py
new file mode 100644
index 000000000..14792bce0
--- /dev/null
+++ b/tests/feature_check/fstring.py
@@ -0,0 +1,3 @@
+# check whether f-strings (PEP-498) are supported
+a = 1
+print(f"a={a}")
diff --git a/tests/feature_check/fstring.py.exp b/tests/feature_check/fstring.py.exp
new file mode 100644
index 000000000..73cdb8bcc
--- /dev/null
+++ b/tests/feature_check/fstring.py.exp
@@ -0,0 +1 @@
+a=1
diff --git a/tests/run-tests.py b/tests/run-tests.py
index 619df5ed3..3e97a7c87 100755
--- a/tests/run-tests.py
+++ b/tests/run-tests.py
@@ -290,6 +290,7 @@ def run_tests(pyb, tests, args, result_dir, num_threads=1):
     skip_const = False
     skip_revops = False
     skip_io_module = False
+    skip_fstring = False
     skip_endian = False
     has_complex = True
     has_coverage = False
@@ -348,6 +349,11 @@ def run_tests(pyb, tests, args, result_dir, num_threads=1):
         if output != b"uio\n":
             skip_io_module = True
 
+        # Check if fstring feature is enabled, and skip such tests if it doesn't
+        output = run_feature_check(pyb, args, base_path, "fstring.py")
+        if output != b"a=1\n":
+            skip_fstring = True
+
         # Check if emacs repl is supported, and skip such tests if it's not
         t = run_feature_check(pyb, args, base_path, "repl_emacs_check.py")
         if "True" not in str(t, "ascii"):
@@ -543,6 +549,7 @@ def run_tests(pyb, tests, args, result_dir, num_threads=1):
         is_async = test_name.startswith(("async_", "uasyncio_"))
         is_const = test_name.startswith("const")
         is_io_module = test_name.startswith("io_")
+        is_fstring = test_name.startswith("string_fstring")
 
         skip_it = test_file in skip_tests
         skip_it |= skip_native and is_native
@@ -555,6 +562,7 @@ def run_tests(pyb, tests, args, result_dir, num_threads=1):
         skip_it |= skip_const and is_const
         skip_it |= skip_revops and "reverse_op" in test_name
         skip_it |= skip_io_module and is_io_module
+        skip_it |= skip_fstring and is_fstring
 
         if args.list_tests:
             if not skip_it: