Add support for basic format strings

3 files changed, 36 insertions, 2 deletions

diff --git a/mesonbuild/interpreterbase.py b/mesonbuild/interpreterbase.py
index 026eaf2..d486b89 100644
--- a/mesonbuild/interpreterbase.py
+++ b/mesonbuild/interpreterbase.py
@@ -708,6 +708,8 @@ class InterpreterBase:
             return self.evaluate_indexing(cur)
         elif isinstance(cur, mparser.TernaryNode):
             return self.evaluate_ternary(cur)
+        elif isinstance(cur, mparser.FormatStringNode):
+            return self.evaluate_fstring(cur)
         elif isinstance(cur, mparser.ContinueNode):
             raise ContinueRequest()
         elif isinstance(cur, mparser.BreakNode):
@@ -926,6 +928,18 @@ The result of this is undefined and will become a hard error in a future Meson r
         else:
             return self.evaluate_statement(node.falseblock)
 
+    def evaluate_fstring(self, node: mparser.FormatStringNode) -> TYPE_var:
+        assert(isinstance(node, mparser.FormatStringNode))
+
+        def replace(match: T.Match[str]) -> str:
+            var = str(match.group(1))
+            try:
+                return str(self.variables[var])
+            except KeyError:
+                raise mesonlib.MesonException(f'Identifier "{var}" does not name a variable.')
+
+        return re.sub(r'{([_a-zA-Z][_0-9a-zA-Z]*)}', replace, node.value)
+
     def evaluate_foreach(self, node: mparser.ForeachClauseNode) -> None:
         assert(isinstance(node, mparser.ForeachClauseNode))
         items = self.evaluate_statement(node.items)
diff --git a/mesonbuild/mparser.py b/mesonbuild/mparser.py
index 79f461e..1079682 100644
--- a/mesonbuild/mparser.py
+++ b/mesonbuild/mparser.py
@@ -114,6 +114,7 @@ class Lexer:
         self.token_specification = [
             # Need to be sorted longest to shortest.
             ('ignore', re.compile(r'[ \t]')),
+            ('fstring', re.compile(r"f'([^'\\]|(\\.))*'")),
             ('id', re.compile('[_a-zA-Z][_0-9a-zA-Z]*')),
             ('number', re.compile(r'0[bB][01]+|0[oO][0-7]+|0[xX][0-9a-fA-F]+|0|[1-9]\d*')),
             ('eol_cont', re.compile(r'\\\n')),
@@ -189,7 +190,7 @@ class Lexer:
                         curl_count -= 1
                     elif tid == 'dblquote':
                         raise ParseException('Double quotes are not supported. Use single quotes.', self.getline(line_start), lineno, col)
-                    elif tid == 'string':
+                    elif tid in {'string', 'fstring'}:
                         # Handle here and not on the regexp to give a better error message.
                         if match_text.find("\n") != -1:
                             mlog.warning(textwrap.dedent("""\
@@ -200,7 +201,7 @@ class Lexer:
                                 str(lineno),
                                 str(col)
                             )
-                        value = match_text[1:-1]
+                        value = match_text[2 if tid == 'fstring' else 1:-1]
                         try:
                             value = ESCAPE_SEQUENCE_SINGLE_RE.sub(decode_match, value)
                         except MesonUnicodeDecodeError as err:
@@ -288,6 +289,14 @@ class StringNode(ElementaryNode[str]):
     def __str__(self) -> str:
         return "String node: '%s' (%d, %d)." % (self.value, self.lineno, self.colno)
 
+class FormatStringNode(ElementaryNode[str]):
+    def __init__(self, token: Token[str]):
+        super().__init__(token)
+        assert isinstance(self.value, str)
+
+    def __str__(self) -> str:
+        return "Format string node: '{self.value}' ({self.lineno}, {self.colno})."
+
 class ContinueNode(ElementaryNode):
     pass
 
@@ -671,6 +680,8 @@ class Parser:
             return NumberNode(t)
         if self.accept('string'):
             return StringNode(t)
+        if self.accept('fstring'):
+            return FormatStringNode(t)
         return EmptyNode(self.current.lineno, self.current.colno, self.current.filename)
 
     def key_values(self) -> ArgumentNode:
diff --git a/test cases/common/238 fstrings/meson.build b/test cases/common/238 fstrings/meson.build
new file mode 100644
index 0000000..ffee053
--- /dev/null
+++ b/test cases/common/238 fstrings/meson.build
@@ -0,0 +1,9 @@
+project('meson-test', 'c')
+
+n = 10
+m = 'bar'
+s = f'test {n} string ({n}): {m}'
+
+if s != 'test 10 string (10): bar'
+  error('Incorrect string formatting')
+endif