cargo: convert TOMLDecodeError or toml2json errors to a MesonException

Avoid getting a raw exception, instead use a (subclass of) MesonException
that is printed in the usual "FILE:LINE:COLUMN: MESSAGE" format.

Fixes: #15023
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

5 files changed, 52 insertions, 3 deletions

diff --git a/mesonbuild/cargo/toml.py b/mesonbuild/cargo/toml.py
index 601510e4e..dda7cfda8 100644
--- a/mesonbuild/cargo/toml.py
+++ b/mesonbuild/cargo/toml.py
@@ -31,17 +31,28 @@ class TomlImplementationMissing(MesonException):
     pass
 
 
+class CargoTomlError(MesonException):
+    """Exception for TOML parsing errors, keeping proper location info."""
+
+
 def load_toml(filename: str) -> T.Dict[str, object]:
     if tomllib:
-        with open(filename, 'rb') as f:
-            raw = tomllib.load(f)
+        try:
+            with open(filename, 'rb') as f:
+                raw = tomllib.load(f)
+        except tomllib.TOMLDecodeError as e:
+            if hasattr(e, 'msg'):
+                raise CargoTomlError(e.msg, file=filename, lineno=e.lineno, colno=e.colno) from e
+            else:
+                raise CargoTomlError(str(e), file=filename) from e
     else:
         if toml2json is None:
             raise TomlImplementationMissing('Could not find an implementation of tomllib, nor toml2json')
 
         p, out, err = Popen_safe([toml2json, filename])
         if p.returncode != 0:
-            raise MesonException('toml2json failed to decode output\n', err)
+            error_msg = err.strip() or 'toml2json failed to decode TOML'
+            raise CargoTomlError(error_msg, file=filename)
 
         raw = json.loads(out)
 
diff --git a/test cases/failing/136 cargo toml error/meson.build b/test cases/failing/136 cargo toml error/meson.build
new file mode 100644
index 000000000..6efaab2c5
--- /dev/null
+++ b/test cases/failing/136 cargo toml error/meson.build
@@ -0,0 +1,19 @@
+project('cargo-toml-error', 'c')
+
+if not add_languages('rust', required: false)
+  error('MESON_SKIP_TEST Rust not present, required for Cargo subprojets')
+endif
+
+# Check if we have tomllib/tomli (not toml2json)
+python = find_program('python3', 'python')
+result = run_command(python, '-c', 'import tomllib', check: false)
+if result.returncode() != 0
+  result = run_command(python, '-c', 'import tomli', check: false)
+  if result.returncode() != 0
+    # Skip test if using toml2json - error format will be different
+    error('MESON_SKIP_TEST toml2json in use, skipping test')
+  endif
+endif
+
+# This should trigger a CargoTomlError with proper location info
+foo_dep = dependency('foo-0')
diff --git a/test cases/failing/136 cargo toml error/subprojects/foo-0-rs.wrap b/test cases/failing/136 cargo toml error/subprojects/foo-0-rs.wrap
new file mode 100644
index 000000000..c39970188
--- /dev/null
+++ b/test cases/failing/136 cargo toml error/subprojects/foo-0-rs.wrap
@@ -0,0 +1,5 @@
+[wrap-file]
+method = cargo
+
+[provide]
+dependency_names = foo-0
diff --git a/test cases/failing/136 cargo toml error/subprojects/foo-0-rs/Cargo.toml b/test cases/failing/136 cargo toml error/subprojects/foo-0-rs/Cargo.toml
new file mode 100644
index 000000000..2f2d7a681
--- /dev/null
+++ b/test cases/failing/136 cargo toml error/subprojects/foo-0-rs/Cargo.toml
@@ -0,0 +1,6 @@
+[package]
+name = "foo"
+version = "0.0.1"
+edition = "2021"
+# This creates a TOML decode error: duplicate key
+name = "bar"
\ No newline at end of file
diff --git a/test cases/failing/136 cargo toml error/test.json b/test cases/failing/136 cargo toml error/test.json
new file mode 100644
index 000000000..480cf64d5
--- /dev/null
+++ b/test cases/failing/136 cargo toml error/test.json
@@ -0,0 +1,8 @@
+{
+  "stdout": [
+    {
+      "match": "re",
+      "line": "test cases/failing/136 cargo toml error/(subprojects/foo-0-rs/Cargo\\.toml:6:13|meson\\.build:19:10): ERROR: Cannot overwrite a value( \\(at.*)?"
+    }
+  ]
+}