data_smart: Make ExpansionErrors more readable

This adds context to ExpansionError messages which show the variable chain for which
expansion is being attempted. This should allow users to debug the issues more easily
than the current message (the first line alone below). Example output from a
SRC_URI which references ${S}:

bb.data_smart.ExpansionError: Failure expanding variable PV, expression was 0.1+git${SRCPV} which triggered exception RecursionError: maximum recursion depth exceeded while calling a Python object
The variable dependency chain for the failure is: PV -> WORKDIR -> S -> SRC_URI -> SRCPV -> PV -> WORKDIR -> S -> SRC_URI -> SRCPV
-> PV -> WORKDIR -> S -> SRC_URI -> SRCPV -> PV -> WORKDIR -> S -> SRC_URI -> SRCPV -> PV -> WORKDIR -> S -> SRC_URI -> SRCPV
-> PV -> WORKDIR -> S -> SRC_URI -> SRCPV -> PV -> WORKDIR -> S -> SRC_URI -> SRCPV -> PV -> WORKDIR -> S -> SRC_URI -> SRCPV
-> PV -> WORKDIR -> S -> SRC_URI -> SRCPV -> PV -> WORKDIR -> S -> SRC_URI -> SRCPV -> PV -> WORKDIR -> S -> SRC_URI -> SRCPV
-> PV -> WORKDIR -> S -> SRC_URI -> SRCPV -> PV -> WORKDIR -> S -> SRC_URI -> SRCPV -> PV -> WORKDIR -> S -> SRC_URI -> SRCPV
-> PV -> WORKDIR -> S -> SRC_URI -> SRCPV -> PV -> WORKDIR -> S -> SRC_URI -> SRCPV -> PV -> WORKDIR -> S -> SRC_URI -> SRCPV
-> PV -> WORKDIR -> S -> SRC_URI -> SRCPV -> PV -> WORKDIR -> S -> SRC_URI -> SRCPV -> PV -> WORKDIR -> S -> SRC_URI -> SRCPV
-> PV -> WORKDIR -> S -> SRC_URI -> SRCPV -> PV -> WORKDIR -> S -> SRC_URI -> SRCPV -> PV -> WORKDIR -> S -> SRC_URI -> SRCPV
-> PV -> WORKDIR -> S -> SRC_URI -> SRCPV -> PV -> WORKDIR -> S -> SRC_URI -> SRCPV -> PV -> WORKDIR -> S -> SRC_URI -> SRCPV
-> PV -> WORKDIR -> S -> SRC_URI -> SRCPV -> PV -> WORKDIR -> S -> SRC_URI -> SRCPV -> PV -> WORKDIR -> S -> SRC_URI -> SRCPV
-> PV -> WORKDIR -> S -> SRC_URI -> SRCPV -> PV -> WORKDIR -> S -> SRC_URI -> SRCPV -> PV -> WORKDIR -> S -> SRC_URI -> SRCPV
-> PV -> WORKDIR -> S -> SRC_URI -> SRCPV -> PV -> WORKDIR -> S -> SRC_URI -> SRCPV -> PV -> WORKDIR -> S -> SRC_URI -> SRCPV
-> PV -> WORKDIR -> S -> SRC_URI -> SRCPV -> PV -> WORKDIR -> S -> SRC_URI -> SRCPV -> PV -> WORKDIR -> S -> SRC_URI -> SRCPV
-> PV -> BP -> FILESPATH

which is more useful that no output. We could truncate at repetition but I suspect
this makes this clearer as it stands so there is little value in complicating the code.

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

1 files changed, 9 insertions, 2 deletions

diff --git a/lib/bb/data_smart.py b/lib/bb/data_smart.py
index 65528c6ae..515d195fe 100644
--- a/lib/bb/data_smart.py
+++ b/lib/bb/data_smart.py
@@ -151,6 +151,7 @@ class ExpansionError(Exception):
         self.expression = expression
         self.variablename = varname
         self.exception = exception
+        self.varlist = [varname or expression]
         if varname:
             if expression:
                 self.msg = "Failure expanding variable %s, expression was %s which triggered exception %s: %s" % (varname, expression, type(exception).__name__, exception)
@@ -160,8 +161,13 @@ class ExpansionError(Exception):
             self.msg = "Failure expanding expression %s which triggered exception %s: %s" % (expression, type(exception).__name__, exception)
         Exception.__init__(self, self.msg)
         self.args = (varname, expression, exception)
+
+    def addVar(self, varname):
+        self.varlist.append(varname)
+
     def __str__(self):
-        return self.msg
+        chain = "\nThe variable dependency chain for the failure is: " + " -> ".join(self.varlist)
+        return self.msg + chain
 
 class IncludeHistory(object):
     def __init__(self, parent = None, filename = '[TOP LEVEL]'):
@@ -407,7 +413,8 @@ class DataSmart(MutableMapping):
                         raise
                 if s == olds:
                     break
-            except ExpansionError:
+            except ExpansionError as e:
+                e.addVar(varname)
                 raise
             except bb.parse.SkipRecipe:
                 raise