Improve support for nested errors (#119)

examples/error/Cargo.toml

@@ -6,4 +6,4 @@ edition = "2018"
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
 [dependencies]
-minijinja = { path = "../../minijinja" }
+minijinja = { path = "../../minijinja", features = ["internal_debug"] }

examples/error/README.md

@@ -5,23 +5,38 @@ template debuggability
 
 ```console
 $ cargo run
-Template Failed Rendering:
-  impossible operation: tried to use + operator on unsupported types number and string (in hello.txt:8)
+Error rendering template: could not render an included template: happend in "include.txt" (in hello.txt:8)
 ---------------------------- Template Source -----------------------------
    5 |             {% with foo = 42 %}
    6 |               {{ range(10) }}
    7 |               {{ other_seq|join(" ") }}
-   8 >               Hello {{ item_squared + bar }}!
+   8 >               {% include "include.txt" %}
+     i                  ^^^^^^^^^^^^^^^^^^^^^ could not render an included template
    9 |             {% endwith %}
   10 |           {% endwith %}
   11 |         {% endfor %}
 --------------------------------------------------------------------------
 Referenced variables: {
-    bar: "test",
-    item_squared: 4,
-    other_seq: [...],
+    other_seq: [
+        0,
+        1,
+        2,
+        3,
+        4,
+    ],
     range: minijinja::functions::builtins::range,
     foo: 42,
 }
 --------------------------------------------------------------------------
+
+caused by: impossible operation: tried to use + operator on unsupported types number and string (in include.txt:1)
+---------------------------- Template Source -----------------------------
+   1 > Hello {{ item_squared + bar }}!
+     i          ^^^^^^^^^^^^^^^^^^ impossible operation
+--------------------------------------------------------------------------
+Referenced variables: {
+    bar: "test",
+    item_squared: 4,
+}
+--------------------------------------------------------------------------
 ```

examples/error/src/main.rs

@@ -1,9 +1,10 @@
 use minijinja::{context, Environment};
 
-fn main() {
+fn execute() -> Result<(), minijinja::Error> {
     let mut env = Environment::new();
     env.set_debug(true);
-    if let Err(err) = env.add_template(
+    env.add_template("include.txt", "Hello {{ item_squared + bar }}!")?;
+    env.add_template(
         "hello.txt",
         r#"
         first line
@@ -12,29 +13,34 @@ fn main() {
             {% with foo = 42 %}
               {{ range(10) }}
               {{ other_seq|join(" ") }}
-              Hello {{ item_squared + bar }}!
+              {% include "include.txt" %}
             {% endwith %}
           {% endwith %}
         {% endfor %}
         last line
         "#,
-    ) {
-        eprintln!("Template Failed Parsing:");
-        eprintln!("  {:#}", err);
-        std::process::exit(1);
-    }
+    )?;
     let template = env.get_template("hello.txt").unwrap();
     let ctx = context! {
         seq => vec![2, 4, 8],
         other_seq => (0..5).collect::<Vec<_>>(),
         bar => "test"
     };
-    match template.render(&ctx) {
-        Ok(result) => println!("{}", result),
-        Err(err) => {
-            eprintln!("Template Failed Rendering:");
-            eprintln!("  {:#}", err);
-            std::process::exit(1);
+    println!("{}", template.render(&ctx)?);
+    Ok(())
+}
+
+fn main() {
+    if let Err(err) = execute() {
+        eprintln!("Error rendering template: {:#}", err);
+
+        let mut err = &err as &dyn std::error::Error;
+        while let Some(next_err) = err.source() {
+            eprintln!();
+            eprintln!("caused by: {:#}", next_err);
+            err = next_err;
         }
+
+        std::process::exit(1);
     }
 }

minijinja/src/compiler/codegen.rs

@@ -244,7 +244,9 @@ impl<'source> CodeGenerator<'source> {
             ast::Stmt::Include(include) => {
                 self.set_line_from_span(include.span());
                 self.compile_expr(&include.name)?;
+                self.push_span(include.span());
                 self.add(Instruction::Include(include.ignore_missing));
+                self.pop_span();
             }
             ast::Stmt::AutoEscape(auto_escape) => {
                 self.set_line_from_span(auto_escape.span());
@@ -312,7 +314,9 @@ impl<'source> CodeGenerator<'source> {
         if let ast::Expr::Call(call) = &expr.expr {
             if let ast::Expr::Var(var) = &call.expr {
                 if var.id == "super" && call.args.is_empty() {
+                    self.push_span(call.span());
                     self.add(Instruction::FastSuper);
+                    self.pop_span();
                     return Ok(());
                 }
                 if var.id == "loop" && call.args.len() == 1 {
@@ -526,6 +530,7 @@ impl<'source> CodeGenerator<'source> {
                 self.sc_bool(matches!(c.op, ast::BinOpKind::ScAnd));
                 self.compile_expr(&c.right)?;
                 self.end_sc_bool();
+                self.pop_span();
                 return Ok(());
             }
             ast::BinOpKind::Add => Instruction::Add,

minijinja/src/compiler/instructions.rs

@@ -262,6 +262,17 @@ impl<'source> Instructions<'source> {
     pub fn add_with_line(&mut self, instr: Instruction<'source>, line: usize) -> usize {
         let rv = self.add(instr);
         self.add_line_record(rv, line);
+
+        // if we follow up to a valid span with no more span, clear it out
+        #[cfg(feature = "debug")]
+        {
+            if self.span_infos.last().map_or(false, |x| x.span.is_some()) {
+                self.span_infos.push(SpanInfo {
+                    first_instruction: rv as u32,
+                    span: None,
+                });
+            }
+        }
         rv
     }
 

minijinja/src/error.rs

@@ -5,7 +5,12 @@ use std::fmt;
 ///
 /// If debug mode is enabled a template error contains additional debug
 /// information that can be displayed by formatting an error with the
-/// alternative formatting (``format!("{:#}", err)``).
+/// alternative formatting (``format!("{:#}", err)``).  That information
+/// is also shown for the [`Debug`] display where the extended information
+/// is hidden when the alternative formatting is used.
+///
+/// Since MiniJinja takes advantage of chained errors it's recommended
+/// to render the entire chain to better understand the causes.
 ///
 /// # Example
 ///
@@ -18,8 +23,14 @@ use std::fmt;
 /// match template.render(ctx) {
 ///     Ok(result) => println!("{}", result),
 ///     Err(err) => {
-///         eprintln!("Could not render template:");
-///         eprintln!("  {:#}", err);
+///         eprintln!("Could not render template: {:#}", err);
+///         // render causes as well
+///         let mut err = &err as &dyn std::error::Error;
+///         while let Some(next_err) = err.source() {
+///             eprintln!();
+///             eprintln!("caused by: {:#}", next_err);
+///             err = next_err;
+///         }
 ///     }
 /// }
 /// ```
@@ -57,10 +68,12 @@ impl fmt::Debug for Error {
         // error struct dump.
         #[cfg(feature = "debug")]
         {
-            if let Some(info) = self.debug_info() {
-                writeln!(f)?;
-                render_debug_info(f, self.kind, self.line(), self.span, info)?;
-                writeln!(f)?;
+            if !f.alternate() {
+                if let Some(info) = self.debug_info() {
+                    writeln!(f)?;
+                    render_debug_info(f, self.kind, self.line(), self.span, info)?;
+                    writeln!(f)?;
+                }
             }
         }
 
@@ -97,6 +110,12 @@ pub enum ErrorKind {
     UndefinedError,
     /// Impossible to serialize this value.
     BadSerialization,
+    /// An error happened in an include.
+    BadInclude,
+    /// An error happened in a super block.
+    EvalBlock,
+    /// Unable to unpack a value.
+    CannotUnpack,
     /// Failed writing output.
     WriteFailure,
 }
@@ -117,6 +136,9 @@ impl ErrorKind {
             ErrorKind::BadEscape => "bad string escape",
             ErrorKind::UndefinedError => "undefined value",
             ErrorKind::BadSerialization => "could not serialize to internal format",
+            ErrorKind::BadInclude => "could not render an included template",
+            ErrorKind::EvalBlock => "could not render block",
+            ErrorKind::CannotUnpack => "cannot unpack",
             ErrorKind::WriteFailure => "failed to write output",
         }
     }

minijinja/src/value/mod.rs

@@ -575,7 +575,7 @@ impl Value {
             ValueRepr::Seq(ref v) => Ok(&v[..]),
             _ => Err(Error::new(
                 ErrorKind::ImpossibleOperation,
-                "value is not a list",
+                format!("value of type {} is not a sequence", self.kind()),
             )),
         }
     }

minijinja/src/vm/mod.rs

@@ -280,7 +280,27 @@ impl<'env> Vm<'env> {
                     state.current_block = Some(name);
                     if let Some(layers) = state.blocks.get(name) {
                         let instructions = layers.first().unwrap();
-                        try_ctx!(self.sub_eval(state, out, instructions, state.blocks.clone()));
+                        let referenced_template = match instructions.name() {
+                            name if name != state.instructions.name() => Some(name),
+                            _ => None,
+                        };
+                        try_ctx!(self
+                            .sub_eval(state, out, instructions, state.blocks.clone())
+                            .map_err(|err| {
+                                Error::new(
+                                    ErrorKind::EvalBlock,
+                                    match referenced_template {
+                                        Some(template) => format!(
+                                            "happend in replaced block \"{}\" of \"{}\"",
+                                            name, template
+                                        ),
+                                        None => {
+                                            format!("happend in local block \"{}\"", name)
+                                        }
+                                    },
+                                )
+                                .with_source(err)
+                            }));
                     } else {
                         bail!(Error::new(
                             ErrorKind::ImpossibleOperation,
@@ -429,7 +449,14 @@ impl<'env> Vm<'env> {
             }
             let original_escape = state.auto_escape;
             state.auto_escape = tmpl.initial_auto_escape();
-            self.sub_eval(state, out, instructions, referenced_blocks)?;
+            self.sub_eval(state, out, instructions, referenced_blocks)
+                .map_err(|err| {
+                    Error::new(
+                        ErrorKind::BadInclude,
+                        format!("happend in \"{}\"", instructions.name()),
+                    )
+                    .with_source(err)
+                })?;
             state.auto_escape = original_escape;
             return Ok(());
         }
@@ -476,7 +503,10 @@ impl<'env> Vm<'env> {
             if capture {
                 out.begin_capture();
             }
-            self.sub_eval(state, out, instructions, state.blocks.clone())?;
+            self.sub_eval(state, out, instructions, state.blocks.clone())
+                .map_err(|err| {
+                    Error::new(ErrorKind::EvalBlock, "happend in super block").with_source(err)
+                })?;
             if capture {
                 Ok(out.end_capture(state.auto_escape))
             } else {
@@ -584,18 +614,14 @@ impl<'env> Vm<'env> {
 
     fn unpack_list(&self, stack: &mut Stack, count: &usize) -> Result<(), Error> {
         let top = stack.pop();
-        let v = top.as_slice().map_err(|e| {
-            Error::new(
-                ErrorKind::ImpossibleOperation,
-                "cannot unpack: not a sequence",
-            )
-            .with_source(e)
-        })?;
+        let v = top
+            .as_slice()
+            .map_err(|e| Error::new(ErrorKind::CannotUnpack, "not a sequence").with_source(e))?;
         if v.len() != *count {
             return Err(Error::new(
-                ErrorKind::ImpossibleOperation,
+                ErrorKind::CannotUnpack,
                 format!(
-                    "cannot unpack: sequence of wrong length (expected {}, got {})",
+                    "sequence of wrong length (expected {}, got {})",
                     *count,
                     v.len()
                 ),
@@ -632,11 +658,15 @@ impl<'env> Vm<'env> {
 }
 
 fn process_err(mut err: Error, pc: usize, state: &State) -> Error {
-    if let Some(span) = state.instructions.get_span(pc) {
-        err.set_filename_and_span(state.instructions.name(), span);
-    } else if let Some(lineno) = state.instructions.get_line(pc) {
-        err.set_filename_and_line(state.instructions.name(), lineno);
+    // only attach line information if the error does not have line info yet.
+    if err.line().is_none() {
+        if let Some(span) = state.instructions.get_span(pc) {
+            err.set_filename_and_span(state.instructions.name(), span);
+        } else if let Some(lineno) = state.instructions.get_line(pc) {
+            err.set_filename_and_line(state.instructions.name(), lineno);
+        }
     }
+    // only attach debug info if we don't have one yet and we are in debug mode.
     #[cfg(feature = "debug")]
     {
         if state.env.debug() && err.debug_info.is_none() {

minijinja/tests/inputs/err_bad_basic_block.txt

@@ -0,0 +1,4 @@
+{}
+---
+{% extends "bad_basic_block.txt" %}
+{% block title %}My Title{% endblock %}

minijinja/tests/inputs/err_bad_block.txt

@@ -0,0 +1,4 @@
+{}
+---
+{% extends "simple_layout.txt" %}
+{% block title %}{{ missing_function() }}{% endblock %}

minijinja/tests/inputs/err_bad_super.txt

@@ -0,0 +1,7 @@
+{}
+---
+{% extends "bad_basic_block.txt" %}
+{% block title %}My Title{% endblock %}
+{% block body %}
+  Changed stuff goes here. {{ super() }}
+{% endblock %}

minijinja/tests/inputs/err_in_include.txt

@@ -0,0 +1,5 @@
+{"seq": [1, 2, 3], "b": []}
+---
+{% for a in seq %}
+  This fails in the include: {% include "a_plus_b.txt" %}
+{% endfor %}

minijinja/tests/inputs/refs/a_plus_b.txt

@@ -0,0 +1 @@
+This template adds b to a: {{ a + b }}

minijinja/tests/inputs/refs/bad_basic_block.txt

@@ -0,0 +1,4 @@
+<title>{% block title %}default title{% endblock %}</title>
+{% block body %}
+  {{ missing_function() }}
+{% endblock %}

minijinja/tests/snapshots/test_templates__vm@block_super_err.txt.snap

@@ -13,11 +13,11 @@ Error {
     line: 1,
 }
 
+impossible operation: cannot super outside of block (in block_super_err.txt:1)
 ---------------------------- Template Source -----------------------------
    1 > {{ super() }}
+     i    ^^^^^^^ impossible operation
 --------------------------------------------------------------------------
 Referenced variables:
 --------------------------------------------------------------------------
 
-
-

minijinja/tests/snapshots/test_templates__vm@debug.txt.snap

@@ -72,6 +72,8 @@ State {
             "urlencode",
         ],
         templates: [
+            "a_plus_b.txt",
+            "bad_basic_block.txt",
             "debug.txt",
             "simple_include.txt",
             "simple_layout.txt",