From f0ac2a35d5e9dfb3a53e6cc810e871fe119cbf4b Mon Sep 17 00:00:00 2001 From: Rebecca Turner Date: Fri, 8 Dec 2023 11:36:57 -0500 Subject: [PATCH] Print the value in `error: cannot coerce` messages (#9553) * Print the value in `error: cannot coerce` messages This extends the `error: cannot coerce a TYPE to a string` message to print the value that could not be coerced. This helps with debugging by making it easier to track down where the value is being produced from, especially in errors with deep or unhelpful stack traces. Co-authored-by: Valentin Gagarin --- .../rl-next/print-value-in-coercion-error.md | 50 +++++++++++++++++++ .../src/language/string-interpolation.md | 2 +- src/libexpr/eval.cc | 10 ++-- ...al-fail-bad-string-interpolation-1.err.exp | 2 +- ...al-fail-bad-string-interpolation-3.err.exp | 2 +- tests/unit/libexpr/error_traces.cc | 28 +++++------ 6 files changed, 73 insertions(+), 21 deletions(-) create mode 100644 doc/manual/rl-next/print-value-in-coercion-error.md diff --git a/doc/manual/rl-next/print-value-in-coercion-error.md b/doc/manual/rl-next/print-value-in-coercion-error.md new file mode 100644 index 00000000000..504ea67b9f1 --- /dev/null +++ b/doc/manual/rl-next/print-value-in-coercion-error.md @@ -0,0 +1,50 @@ +synopsis: Coercion errors include the failing value +issues: #561 +prs: #9553 +description: { + +The `error: cannot coerce a to a string` message now includes the value which caused the error. + +Previously, a failed string coercion produced a confusing error message if the trace didn't show where the offending value was defined: + +```bash +$ nix-instantiate --eval --expr ' +let x = { a = 1; }; in + +"${x}" +' +error: + … while evaluating a path segment + + at «string»:4:2: + + 3| + 4| "${x}" + | ^ + 5| + + error: cannot coerce a set to a string +``` + +Now, the error message includes the value itself: + +```bash +$ nix-instantiate --eval --expr ' +let x = { a = 1; }; in + +"${x}" +' +error: + … while evaluating a path segment + + at «string»:4:2: + + 3| + 4| "${x}" + | ^ + 5| + + error: cannot coerce a set to a string: { a = 1; } +``` + +} diff --git a/doc/manual/src/language/string-interpolation.md b/doc/manual/src/language/string-interpolation.md index e999b287b9c..6e28d26646b 100644 --- a/doc/manual/src/language/string-interpolation.md +++ b/doc/manual/src/language/string-interpolation.md @@ -189,7 +189,7 @@ If neither is present, an error is thrown. > "${a}" > ``` > -> error: cannot coerce a set to a string +> error: cannot coerce a set to a string: { } > > at «string»:4:2: > diff --git a/src/libexpr/eval.cc b/src/libexpr/eval.cc index 7e68e6f9b74..b52274b64e1 100644 --- a/src/libexpr/eval.cc +++ b/src/libexpr/eval.cc @@ -26,9 +26,9 @@ #include #include #include -#include #include #include +#include #include #include @@ -2286,7 +2286,7 @@ BackedStringView EvalState::coerceToString( return std::move(*maybeString); auto i = v.attrs->find(sOutPath); if (i == v.attrs->end()) { - error("cannot coerce %1% to a string", showType(v)) + error("cannot coerce %1% to a string: %2%", showType(v), printValue(*this, v)) .withTrace(pos, errorCtx) .debugThrow(); } @@ -2332,7 +2332,7 @@ BackedStringView EvalState::coerceToString( } } - error("cannot coerce %1% to a string", showType(v)) + error("cannot coerce %1% to a string: %2%", showType(v), printValue(*this, v)) .withTrace(pos, errorCtx) .debugThrow(); } @@ -2691,8 +2691,10 @@ void EvalState::printStatistics() std::string ExternalValueBase::coerceToString(const Pos & pos, NixStringContext & context, bool copyMore, bool copyToStore) const { + std::strstream printed; + print(printed); throw TypeError({ - .msg = hintfmt("cannot coerce %1% to a string", showType()) + .msg = hintfmt("cannot coerce %1% to a string: %2%", showType(), printed.str()) }); } diff --git a/tests/functional/lang/eval-fail-bad-string-interpolation-1.err.exp b/tests/functional/lang/eval-fail-bad-string-interpolation-1.err.exp index eb73e9a5298..e54ecc6d1a7 100644 --- a/tests/functional/lang/eval-fail-bad-string-interpolation-1.err.exp +++ b/tests/functional/lang/eval-fail-bad-string-interpolation-1.err.exp @@ -7,4 +7,4 @@ error: | ^ 2| - error: cannot coerce a function to a string + error: cannot coerce a function to a string: diff --git a/tests/functional/lang/eval-fail-bad-string-interpolation-3.err.exp b/tests/functional/lang/eval-fail-bad-string-interpolation-3.err.exp index ac14f329b78..6f0a96f78dd 100644 --- a/tests/functional/lang/eval-fail-bad-string-interpolation-3.err.exp +++ b/tests/functional/lang/eval-fail-bad-string-interpolation-3.err.exp @@ -7,4 +7,4 @@ error: | ^ 2| - error: cannot coerce a function to a string + error: cannot coerce a function to a string: diff --git a/tests/unit/libexpr/error_traces.cc b/tests/unit/libexpr/error_traces.cc index 81498f65a3f..c2403bee938 100644 --- a/tests/unit/libexpr/error_traces.cc +++ b/tests/unit/libexpr/error_traces.cc @@ -295,7 +295,7 @@ namespace nix { TEST_F(ErrorTraceTest, toPath) { ASSERT_TRACE2("toPath []", TypeError, - hintfmt("cannot coerce %s to a string", "a list"), + hintfmt("cannot coerce %s to a string: %s", "a list", "[ ]"), hintfmt("while evaluating the first argument passed to builtins.toPath")); ASSERT_TRACE2("toPath \"foo\"", @@ -309,7 +309,7 @@ namespace nix { TEST_F(ErrorTraceTest, storePath) { ASSERT_TRACE2("storePath true", TypeError, - hintfmt("cannot coerce %s to a string", "a Boolean"), + hintfmt("cannot coerce %s to a string: %s", "a Boolean", "true"), hintfmt("while evaluating the first argument passed to 'builtins.storePath'")); } @@ -318,7 +318,7 @@ namespace nix { TEST_F(ErrorTraceTest, pathExists) { ASSERT_TRACE2("pathExists []", TypeError, - hintfmt("cannot coerce %s to a string", "a list"), + hintfmt("cannot coerce %s to a string: %s", "a list", "[ ]"), hintfmt("while realising the context of a path")); ASSERT_TRACE2("pathExists \"zorglub\"", @@ -332,7 +332,7 @@ namespace nix { TEST_F(ErrorTraceTest, baseNameOf) { ASSERT_TRACE2("baseNameOf []", TypeError, - hintfmt("cannot coerce %s to a string", "a list"), + hintfmt("cannot coerce %s to a string: %s", "a list", "[ ]"), hintfmt("while evaluating the first argument passed to builtins.baseNameOf")); } @@ -377,7 +377,7 @@ namespace nix { TEST_F(ErrorTraceTest, filterSource) { ASSERT_TRACE2("filterSource [] []", TypeError, - hintfmt("cannot coerce %s to a string", "a list"), + hintfmt("cannot coerce %s to a string: %s", "a list", "[ ]"), hintfmt("while evaluating the second argument (the path to filter) passed to 'builtins.filterSource'")); ASSERT_TRACE2("filterSource [] \"foo\"", @@ -1038,7 +1038,7 @@ namespace nix { TEST_F(ErrorTraceTest, toString) { ASSERT_TRACE2("toString { a = 1; }", TypeError, - hintfmt("cannot coerce %s to a string", "a set"), + hintfmt("cannot coerce %s to a string: %s", "a set", "{ a = 1; }"), hintfmt("while evaluating the first argument passed to builtins.toString")); } @@ -1057,7 +1057,7 @@ namespace nix { ASSERT_TRACE2("substring 0 3 {}", TypeError, - hintfmt("cannot coerce %s to a string", "a set"), + hintfmt("cannot coerce %s to a string: %s", "a set", "{ }"), hintfmt("while evaluating the third argument (the string) passed to builtins.substring")); ASSERT_TRACE1("substring (-3) 3 \"sometext\"", @@ -1070,7 +1070,7 @@ namespace nix { TEST_F(ErrorTraceTest, stringLength) { ASSERT_TRACE2("stringLength {} # TODO: context is missing ???", TypeError, - hintfmt("cannot coerce %s to a string", "a set"), + hintfmt("cannot coerce %s to a string: %s", "a set", "{ }"), hintfmt("while evaluating the argument passed to builtins.stringLength")); } @@ -1143,7 +1143,7 @@ namespace nix { ASSERT_TRACE2("concatStringsSep \"foo\" [ 1 2 {} ] # TODO: coerce to string is buggy", TypeError, - hintfmt("cannot coerce %s to a string", "an integer"), + hintfmt("cannot coerce %s to a string: %s", "an integer", "1"), hintfmt("while evaluating one element of the list of strings to concat passed to builtins.concatStringsSep")); } @@ -1229,12 +1229,12 @@ namespace nix { ASSERT_TRACE2("derivationStrict { name = \"foo\"; builder = 1; system = {}; }", TypeError, - hintfmt("cannot coerce %s to a string", "a set"), + hintfmt("cannot coerce %s to a string: %s", "a set", "{ }"), hintfmt("while evaluating the attribute 'system' of derivation 'foo'")); ASSERT_TRACE2("derivationStrict { name = \"foo\"; builder = 1; system = 1; outputs = {}; }", TypeError, - hintfmt("cannot coerce %s to a string", "a set"), + hintfmt("cannot coerce %s to a string: %s", "a set", "{ }"), hintfmt("while evaluating the attribute 'outputs' of derivation 'foo'")); ASSERT_TRACE2("derivationStrict { name = \"foo\"; builder = 1; system = 1; outputs = \"drv\"; }", @@ -1279,17 +1279,17 @@ namespace nix { ASSERT_TRACE2("derivationStrict { name = \"foo\"; builder = 1; system = 1; outputs = \"out\"; args = [ {} ]; }", TypeError, - hintfmt("cannot coerce %s to a string", "a set"), + hintfmt("cannot coerce %s to a string: %s", "a set", "{ }"), hintfmt("while evaluating an element of the argument list")); ASSERT_TRACE2("derivationStrict { name = \"foo\"; builder = 1; system = 1; outputs = \"out\"; args = [ \"a\" {} ]; }", TypeError, - hintfmt("cannot coerce %s to a string", "a set"), + hintfmt("cannot coerce %s to a string: %s", "a set", "{ }"), hintfmt("while evaluating an element of the argument list")); ASSERT_TRACE2("derivationStrict { name = \"foo\"; builder = 1; system = 1; outputs = \"out\"; FOO = {}; }", TypeError, - hintfmt("cannot coerce %s to a string", "a set"), + hintfmt("cannot coerce %s to a string: %s", "a set", "{ }"), hintfmt("while evaluating the attribute 'FOO' of derivation 'foo'")); }